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Acetylene, The Principles Of Its Generation And Use by F. H. Leeds and W. J. Atkinson Butterfield

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Second Edition









In compiling this work on the uses and application of acetylene, the
special aim of the authors has been to explain the various physical and
chemical phenomena:

(1) Accompanying the generation of acetylene from calcium carbide and

(2) Accompanying the combustion of the gas in luminous or incandescent
burners, and

(3) Its employment for any purpose--(a) neat, (b) compressed into
cylinders, (c) diluted, and (d) as an enriching material.

They have essayed a comparison between the value of acetylene and other
illuminants on the basis of "illuminating effect" instead of on the
misleading basis of pure "illuminating power," a distinction which they
hope and believe will do much to clear up the misconceptions existing on
the subject. Tables are included, for the first time (it is believed) in
English publications, of the proper sizes of mains and service-pipes for
delivering acetylene at different effective pressures, which, it is
hoped, will prove of use to those concerned in the installation of
acetylene lighting systems.

_June_ 1903


The revision of this work for a new edition was already far advanced when
it was interrupted by the sudden death on April 30, 1908, of Mr. F. H.
Leeds. The revision was thereafter continued single-handed, with the help
of very full notes which Mr. Leeds had prepared, by the undersigned. It
had been agreed prior to Mr. Leeds' death that it would add to the
utility of the work if descriptions of a number of representative
acetylene generators were given in an Appendix, such as that which now
appears at the conclusion of this volume. Thanks are due to the numerous
firms and individuals who have assisted by supplying information for use
in this Appendix.



_August 1909_




Intrinsic advantages
Hygienic advantages
Acetylene and paraffin oil
Blackened ceilings
Cost of acetylene lighting
Cost of acetylene and coal-gas
Cost of acetylene and electric lighting
Cost of acetylene and paraffin oil
Cost of acetylene and air-gas
Cost of acetylene and candles
Tabular statement of costs (_to face_)
Illuminating power and effect



Nature of calcium carbide
Storage of calcium carbide
Fire risks of acetylene lighting
Purchase of carbide
Quality and sizes of carbide
Treated and scented carbide
Reaction between carbide and water
chemical nature
heat evolved
difference between heat and temperature
amount of heat evolved
effect of heat on process of generation
effects of heat
effect of heat on the chemical reaction
effects of heat on the acetylene
effects of heat on the carbide
Colour of spent carbide
Maximum attainable temperatures
Soft solder in generators
Reactions at low temperatures
Reactions at high temperatures
Pressure in generators



Automatic and non-automatic generators
Control of the chemical reaction
Non-automatic carbide-to-water generators
Non-automatic water-to-carbide generators
Automatic devices
Displacement gasholders
Action of water-to-carbide generators
Action of carbide-to-water generators
Use of oil in generator
Rising gasholder
Deterioration of acetylene on storage
Freezing and its avoidance
Corrosion in apparatus
Isolation of holder from generator
Vent pipes and safety valve
Frothing in generator
Dry process of generation
Artificial lighting of generator sheds



Points to be observed
Recommendations of Home Office Committee
British and Foreign regulations for the construction and installation of
acetylene generating plant



Impurities in calcium carbide
Impurities of acetylene
Removal of moisture
Generator impurities in acetylene
Carbide impurities in acetylene
Reasons for purification
Necessary extent of purification
Quantity of impurities in acetylene
Purifying materials
Bleaching powder
Heratol, frankoline, acagine, and puratylene
Efficiency of purifying material
Minor reagent
Method of a gas purifier
Methods of determining exhaustion of purifying material
Regulations for purification
Position of purifier
General arrangement of plans
Generator residues
Disposal of residue



Physical properties
Heat of combustion
Explosive limits
Range of explosibility
Solubility in liquids
Endothermic nature
Heats of formation and combustion
Colour of flame
Radiant efficiency
Chemical properties
Reactions with copper



Gasholder pressure
Dimensions of mains and pipes
Velocity of flow in pipes
Service-pipes and mains
Pipes and fittings
Laying mains
Expelling air from pipes
Tables of pipes and mains



Nature of luminous flames
Illuminating power
Early burners
Injector and twin-flame burners
Illuminating power of self-luminous burners
Glassware for burners



Merits of incandescent lighting
Conditions for incandescent lighting
Illuminating power of incandescent burners
Durability of mantles
Typical incandescent burners
Acetylene for heating and cooking
Acetylene motors
Autogenous soldering and welding



Carburetted acetylene
Illuminating power of carburetted acetylene
Carburetted acetylene for "power"



Dissolved acetylene
Solution in acetone
Liquefied acetylene
Dilution with carbon dioxide
Dilution with air
Mixed carbides
Dilution with, methane and hydrogen
Self-inflammable acetylene
Enrichment with acetylene
Partial pressure



Destruction of noxious moths
Destruction of phylloxera and mildew
Manufacture of lampblack
Production of tetrachlorethane
Utilisation of residues
Sundry uses for the gas



Table and vehicular lamps
Flare lamps
Cartridges of carbide
Cycle-lamp burners
Railway lighting



Regulations of British Acetylene Association
Regulations oL German Acetylene Association
Regulations of Austrian Acetylene Association
Sampling carbide
Yield of gas from small carbide
Correction of volumes for temperature and pressure
Estimation of impurities
Tabular numbers



America: Canada
America: United States
Great Britain and Ireland






Acetylene is a gas [Footnote: For this reason the expression, "acetylene
gas," which is frequently met with, would be objectionable on the ground
of tautology, even if it were not grammatically and technically
incorrect. "Acetylene-gas" is perhaps somewhat more permissible, but it
is equally redundant and unnecessary.] of which the most important
application at the present time is for illuminating purposes, for which
its properties render it specially well adapted. No other gas which can
be produced on a commercial scale is capable of giving, volume for
volume, so great a yield of light as acetylene. Hence, apart from the
advantages accruing to it from its mode of production and the nature of
the raw material from which it is produced, it possesses an inherent
advantage over other illuminating gases in the smaller storage
accommodation and smaller mains and service-pipes requisite for the
maintenance of a given supply of artificial light. For instance, if a
gasholder is required to contain sufficient gas for the lighting of an
establishment or district for twenty-four hours, its capacity need not be
nearly so great if acetylene is employed as if oil-gas, coal-gas, or
other illuminating gas is used. Consequently, for an acetylene supply the
gasholder can be erected on a smaller area and for considerably less
outlay than for other gas supplies. In this respect acetylene has an
unquestionable economical advantage as a competitor with other varieties
of illuminating gas for supplies which have generally been regarded as
lying peculiarly within their preserves. The extent of this advantage
will be referred to later.

The advantages that accrue to acetylene from its mode of production, and
the nature of the raw material from which it is obtained, are in reality
of more importance. Acetylene is readily and quickly produced from a raw
material--calcium carbide--which, relatively to the yield of light of the
gaseous product, is less bulky than the raw materials of other gases. In
comparison also with oils and candles, calcium carbide is capable of
yielding, through the acetylene obtainable from it, more light per unit
of space occupied by it. This higher light-yielding capacity of calcium
carbide, ready to be developed through acetylene, gives the latter gas a
great advantage over all other illuminants in respect of compactness for
transport or storage. Hence, where facilities for transport or storage
are bad or costly, acetylene may be the most convenient or cheapest
illuminant, notwithstanding its relatively high cost in many other cases.
For example, in a district to which coal and oil must be brought great
distances, the freight on them may be so heavy that--regarding the
question as simply one of obtaining light in the cheapest manner--it may
be more economical to bring calcium carbide an equal or even greater
distance and generate acetylene from it on the spot, than to use oil or
make coal-gas for lighting purposes, notwithstanding that acetylene may
not be able to compete on equal terms with oil--or coal-gas at the place
from which the carbide is brought. Likewise where storage accommodation
is limited, as in vehicles or in ships or lighthouses, calcium carbide
may be preferable to oil or other illuminants as a source of light.
Disregarding for the moment intrinsic advantages which the light
obtainable from acetylene has over other lights, there are many cases
where, owing to saving in cost of carriage, acetylene is the most
economical illuminant; and many other cases where, owing to limited space
for storage, acetylene far surpasses other illuminants in convenience,
and is practically indispensable.

The light of the acetylene flame has, however, some intrinsic advantages
over the light of other artificial illuminants. In the first place, the
light more closely resembles sunlight in composition or "colour." It is
more nearly a pure "white" light than is any other flame or incandescent
body in general use for illuminating purposes. The nature or composition
of the light of the acetylene flame will be dealt with more exhaustively
later, and compared with that afforded by other illuminants; but,
speaking generally, it may be said that the self-luminous acetylene light
is superior in tint, to all other artificial lights, for which reason it
is invaluable for colour-judging and shade-matching. In the second
place, when the gas issues from a suitable self-luminous burner under
proper pressure, the acetylene flame is perfectly steady; and in this
respect it in preferable to most types of electric light, to all self-
luminous coal-gas flames and candles, and to many varieties of oil-lamp.
In steadiness and freedom from flicker it is fully equal to incandescent
coal-gas light, but it in distinctly superior to the latter by virtue of
its complete freedom from noise. The incandescent acetylene flame emits a
slight roaring, but usually not more than that coming from an
atmospheric coal-gas burner. With the exception of the electric arc,
self-luminous acetylene yields a flame of unsurpassed intensity, and yet
its light is agreeably soft. In the third place, where electricity is
absent, a brilliancy of illumination which can readily be obtained from
self-luminous acetylene can otherwise only be procured by the employment
of the incandescent system applied either to coal-gas or to oil; and
there are numerous situations, such as factories, workshops, and the
like, where the vibration of the machinery or the prevalence of dust
renders the use of mantles troublesome if not impossible. Anticipating
what will be said later, in cases like these, the cost of lighting by
self-luminous acetylene may fairly be compared with self-luminous coal-
gas or oil only; although in other positions the economy of the Welsbach
mantle must be borne in mind.

Acetylene lighting presents also certain important hygienic advantages
over other forms of flame lighting, in that it exhausts, vitiates, and
heats the air of a room to a less degree, for a given yield of light,
than do either coal-gas, oils, or candles. This point in favour of
acetylene is referred to here only in general terms; the evidence on
which the foregoing statement is based will be recorded in a tabular
comparison of the cost and qualities of different illuminants. Exhaustion
of the air means, in this connexion, depletion of the oxygen normally
present in it. One volume of acetylene requires 2-1/2 volumes of oxygen
for its complete combustion, and since 21 volumes of oxygen are
associated in atmospheric air with 79 volumes of inert gases--chiefly
nitrogen--which do not actively participate in combustion, it follows
that about 11.90 volumes of air are wholly exhausted, or deprived of
oxygen, in the course of the combustion of one volume of acetylene. If
the light which may be developed by the acetylene is brought into
consideration, it will be found that, relatively to other illuminants,
acetylene causes less exhaustion of the air than any other illuminating
agent except electricity. For instance, coal-gas exhausts only about 6-
1/2 times its volume of air when it is burnt; but since, volume for
volume, acetylene ordinarily yields from three to fifteen times as much
light as coal-gas, it follows that the same illuminative value is
obtainable from acetylene by considerably less exhaustion of the air than
from coal-gas. The exact ratio depends on the degree of efficiency of the
burners, or of the methods by which light is obtained from the gases, as
will be realised by reference to the table which follows. Broadly
speaking, however, no illuminant which evolves light by combustion
(oxidation), and which therefore requires a supply of oxygen or air for
its maintenance, affords light with so little exhaustion of the air as
acetylene. Hence in confined, ill-ventilated, or crowded rooms, the air
will suffer less exhaustion, and accordingly be better for breathing, if
acetylene is chosen rather than any other illuminant, except electricity.

Next, in regard to vitiation of the air, by which is meant the alteration
in its composition resulting from the admixture of products of combustion
with it. Electric lighting is as superior to other modes of lighting in
respect of direct vitiation as of exhaustion of the air, because it does
not depend on combustion. Putting it aside, however, light is obtainable
by means of acetylene with less attendant vitiation of the air than by
means of any other gas or of oil or candles. The principal vitiating
factor in all cases is the carbonic acid produced by the combustion. Now
one volume of acetylene on combustion yields two volumes of carbonic
acid, whereas one volume of coal-gas yields about 0.6 volume of carbonic
acid. But even assuming that the incandescent system of lighting is
applied in the case of coal-gas and not of acetylene, the ratio of the
consumption of the two gases for the development of a given illuminative
effect will be such that no more carbonic acid will be produced by the
acetylene; and if the incandescent system is applied either in both cases
or in neither, the ratio will be greatly in favour of acetylene. The
other factors which determine the vitiation of the air of a room in which
the gas is burning are likewise under ordinary conditions more in favour
of acetylene. They are not, however, constant, since the so-called
"impurities," which on combustion cause vitiation of the air, vary
greatly in amount according to the extent to which the gases have been
purified. London coal-gas, which was formerly purified to the highest
degree practically attainable, used to contain on the average only 10 to
12 grains of sulphur per 100 cubic feet, and virtually no other impurity.
But now coal-gas, in London and most provincial towns, contains 40 to 50
grains of sulphur per 100 cubic foot. At least 5 grains of ammonia per
100 cubic foot in also present in coal-gas in some towns. Crude acetylene
also contains sulphur and ammonia, that coming from good quality calcium
carbide at the present day including about 31 grains of the former and
25 grains of the latter per 100 cubic feet. But crude acetylene is also
accompanied by a third impurity, viz., phosphoretted hydrogen or
phosphine, which in unknown in coal-gas, and which is considerably more
objectionable than either ammonia or sulphur. The formation, behaviour,
and removal of those various impurities will be discussed in Chapter V.;
but here it may be said that there is no reason why, if calcium carbide
of a fair degree of purity has been used, and if the gas has been
generated from it in a properly designed and smoothly working apparatus--
this being quite as important as, or even more important than, the purity
of the original carbide--the gas should not be freed from phosphorus,
sulphur, and ammonia to the utmost necessary or desirable extent, by
processes which are neither complicated nor expensive. And if this is
done, as it always should be whenever the acetylene is required for
domestic lighting, the vitiation of the air of a room due to the
"impurities" in the gas will become much less in the case of acetylene
than in that of even well-purified coal-gas; taking equal illuminating
effect as the basis for comparison.

Acetylene is similarly superior, speaking generally, to petroleum in
respect of impurities, though the sulphur present in petroleum oils, such
as are sold in this country for household use, though very variable, is
often quite small in amount, and seldom is responsible for serious
vitiation of the atmosphere.

Regarding somewhat more closely the relative convenience and safety of
acetylene and paraffin for the illumination of country residences, it may
be remarked that an extraordinarily great amount of care must he bestowed
upon each separate lamp if the whole house is to be kept free from an
odour which is very offensive to the nostrils; and the time occupied in
this process, which of itself is a disagreeable one, reaches several
hours every day. Habit has taught the country dweller to accept as
inevitable this waste of time, and largely to ignore the odour of
petroleum in his abode; but the use of acetylene entirely does away with
the daily cleaning of lamps, and, if the pipe-fitting work has been done
properly, yields light absolutely unaccompanied by smell. Again, unless
most carefully managed, the lamp-room of a large house, with its store of
combustible oil, and its collection of greasy rags, must unavoidably
prove a sensible addition to the risk of fire. The analogue of the lamp-
room when acetylene is employed is the generator-house, and this is a
separate building at some distance from the residence proper. There need
be no appreciable odour in the generator-house, except during the times
of charging the apparatus; but if there is, it passes into the open air
instead of percolating into the occupied apartments.

The amount of heat developed by the combustion of acetylene also is less
for a given yield of light than that developed by most other illuminants.
The gas, indeed, is a powerful heating gas, but owing to the amount
consumed being so small in proportion to the light developed, the heat
arising from acetylene lighting in a room is less than that from most
other illuminating agents, if the latter are employed to the extent
required to afford equally good illumination. The ratio of the heat
developed in acetylene lighting to that developed in, _e.g._,
lighting by ordinary coal-gas, varies considerably according to the
degree of efficiency of the burners, or, in other words, of the methods
by which light is obtained from the gases. Volume for volume, acetylene
yields on combustion about three and a half times as much heat as coal-
gas, yet, owing to its superior efficiency as an illuminant, any required
light may be obtained through it with no greater evolution of heat than
the best practicable (incandescent) burners for coal-gas produce. The
heat evolved by acetylene burners adequate to yield a certain light is
very much less than that evolved by ordinary flat-flame coal-gas burners
or by oil-lamps giving the same light, and is not more than about three
times as much as that from ordinary electric lamps used in numbers
sufficient to give the same light. More exact figures for the ratio
between the heat developed in acetylene lighting and that in other modes
of lighting are given in the table already referred to.

In connexion with the smaller amount of heat developed per unit of light
when acetylene is the illuminant, the frequently exaggerated claim that
acetylene does not blacken ceilings at all may be studied. Except it be a
carelessly manipulated petroleum-lamp, no form of artificial illuminant
employed nowadays ever emits black smoke, soot, or carbon, in spite of
the fact that all luminous flames commercially capable of utilisation do
contain free carbon in the elemental state. The black mark on a ceiling
over a source of light is caused by a rising current of hot air and
combustion products set up by the heat accompanying the light, which
current of hot gas carries with it the dust and dirt always present in
the atmosphere of an inhabited room. As this current of air and burnt gas
travels in a fairly concentrated vertical stream, and as the ceiling is
comparatively cool and exhibits a rough surface, that dust and dirt are
deposited on the ceiling above the flame, but the stain is seldom or
never composed of soot from the illuminant itself. Proof of this
statement may be found in the circumstance that a black mark is
eventually produced over an electric glow-lamp and above a pipe
delivering hot water. Clearly, therefore, the depth and extent of the
mark will depend on the volume and temperature of the hot gaseous
current; and since per unit of light acetylene emits a far smaller
quantity of combustion products and a far smaller amount of heat than any
other flame illuminant except incandescent coal-gas, the inevitable black
mark over its flame takes very much longer to appear. Quite roughly
speaking, as may be deduced from what has already been said on this
subject, the luminous flame of acetylene "blackens" a ceiling at about
the same rate as a coal-gas burner of the best Welsbach type.

There is one respect in which acetylene and other flame illuminants are
superior to electric lighting, viz., that they sterilise a larger volume
of air. All the air which is needed to support combustion, as well as the
excess of air which actually passes through the burner tube and flame in
incandescent burners, is obviously sterilised; but so also is the much
larger volume of air which, by virtue of the up-current due to the heat
of the flame, is brought into anything like close proximity with the
light. The electric glow-lamp, and the most popular and economical modern
enclosed electric arc-lamp, sterilise only the much smaller volume of air
which is brought into direct contact with their glass bulbs. Moreover,
when large numbers of persons are congregated in insufficiently
ventilated buildings--and many public rooms are insufficiently
ventilated--the air becomes nauseous to inspire and positively
detrimental to the health of delicate people, by reason of the human
effluvia which arise from soiled raiment and uncleansed or unhealthy
bodies, long before the proportion of carbonic acid by itself is high
enough to be objectionable. Thus a certain proportion of carbonic acid
coming from human lungs and skin is more harmful than the same proportion
of carbonic acid derived from the combustion of gas or oil. Hence
acetylene and flame illuminants generally have the valuable hygienic
advantages over electric lighting, not only of killing a far larger
number of the micro-organisms that may be present in the air, but, by
virtue of their naked flames, of burning up and destroying a considerable
quantity of the aforesaid odoriferous matter, thus relieving the nose and
materially assisting in the prevention of that lassitude and anaemia
occasionally follow the constant inspiration of air rendered foul by
human exhalations.

The more important advantages of acetylene as an illuminant have now been
indicated, and it remains to discuss the cost of acetylene lighting in
comparison with other modes of procuring artificial light. At the outset
it may be stated that a very much greater reduction in the price of
calcium carbide--from which acetylene is produced--than is likely to
ensue under the present methods and conditions of manufacture will be
required to make acetylene lighting as cheap as ordinary gas lighting in
towns in this country, provided incandescent burners are used for the
gas. On the score of cheapness (and of convenience, unless the acetylene
were delivered to the premises from some central generating station)
acetylene cannot compete as an illuminant with coal-gas where the latter
costs, say, not more than 5s. per 1000 cubic feet, if only
reasonable attention is given to the gas-burners, and at least a quarter
of them are on the incandescent system. If, on the other hand, coal-gas
is misused and wasted through the employment only of interior or worn-out
flat-flame burners, while the best types of burner are used for
acetylene, the latter gas may prove as cheap for lighting as coal-gas at,
say, 2s. 6d. per 1000 cubic feet (and be far better hygienically);
whereas, contrariwise, if coal-gas is used only with good and properly
maintained incandescent burners, it may cost over 10s. per 1000 cubic
feet, and be cheaper than acetylene burned in good burners (and as good
from the hygienic standpoint). More precise figures on the relative costs
of coal-gas lighting and acetylene lighting are given in the tabular
statement at the close of this chapter.

With regard to electric lighting it is somewhat difficult to lay down a
fair basis of comparison, owing to the wide variations in the cost of
current, and in the efficiency of lamps, and to the undoubted hygienic
and aesthetic claims of electric lighting to precedence. But in towns in
this country where there is a public electricity supply, electric
lighting will be used rather than acetylene for the same reasons that it
is preferred to coal-gas. Cost is only a secondary consideration in such
cases, and where coal-gas is reasonably cheap, and nevertheless gives
place to electric lighting, acetylene clearly cannot hope to supplant the
latter. [Footnote: Where, however, as is frequently the case with small
public electricity-supply works, the voltage of the supply varies
greatly, the fluctuations in the light of the lamps, and the frequent
destruction of fuses and lamps, are such manifest inconveniences that
acetylene is in fact now being generally preferred to electric lighting
in such circumstances.] But where current cannot be had from an
electricity-supply undertaking, and it is a question, in the event of
electric lighting being adopted, of generating current by driving a
dynamo, either by means of a gas-engine supplied from public gas-mains,
by means of a special boiler installation, or by means of an oil-engine
or of a power gas-plant and gas-engine, the claims of acetylene to
preference are very strong. An important factor in the estimation of the
relative advantages of electricity and acetylene in such cases is the
cost of labour in looking after the generating plant. Where a gas-engine
supplied from public gas-mains is used for driving the dynamo, electric
lighting can be had at a relatively small expenditure for attendance on
the generating plant. But the cost of the gas consumed will be high, and
actually light could be obtained directly from the gas by means of
incandescent mantles at far loss cost than by consuming the gas in a
motor for the indirect production of light by means of electric current.
Therefore electric lighting, if adopted under these conditions, must be
preferred to gas lighting from considerations which are deemed to
outweigh those of a much higher cost, and acetylene does not present so
great advantages over coal-gas as to affect the choice of electric
lighting. But in the cases where there is no public gas-supply, and
current must be generated from coal or coke or oil consumed on the spot,
the cost of the skilled labour required to look after either a boiler,
steam-engine and dynamo, or a power gas-plant and gas-engine or oil-
engine and dynamo, will be so heavy that unless the capacity of the
installation is very great, acetylene will almost certainly prove a
cheaper and more convenient method of obtaining light. The attention
required by an acetylene installation, such as a country house of upwards
of thirty rooms would want, is limited to one or two hours' labour per
diem at any convenient time during daylight. Moreover, the attendant need
not be highly paid, as he will not have required an engineman's training,
as will the attendant on an electric lighting plant. The latter, too,
must be present throughout the hours when light is wanted unless a heavy
expenditure has been incurred on accumulators. Furthermore, the capital
outlay on generating plant will be very much less for acetylene than for
electric lighting. General considerations such as these lead to the
conclusion that in almost all country districts in this country a house
or institution could be lighted more cheaply by means of acetylene than
by electricity. In the tabular statement of comparative costs of
different modes of lighting, electric lighting has been included only on
the basis of a fixed cost per unit, as owing to the very varied cost of
generating current by small installations in different parts of the
country it would be futile to attempt to give the cost of electric
lighting on any other basis, such as the prime cost of coal or coke in a
particular district. Where current is supplied by a public electricity-
supply undertaking, the cost per unit is known, and the comparative costs
of electric light and acetylene can be arrived at with tolerable
precision. It has not been thought necessary to include in the tabular
statement electric arc-lamps, as they are only suitable for the lighting
of large spaces, where the steadiness and uniformity of the illumination
are of secondary importance. Under such conditions, it may be stated
parenthetically, the electric arc-light is much less costly than
acetylene lighting would be, but it is now in many places being
superseded by high-pressure gas or oil incandescent lights, which are
steady and generally more economical than the arc light.

The illuminant which acetylene is best fitted to supersede on the score
of convenience, cleanliness, and hygienic advantages is oil. By oil is
meant, in this connection, the ordinary burning petroleum, kerosene, or
paraffin oil, obtained by distilling and refining various natural oils
and shales, found in many countries, of which the United States
(principally Pennsylvania), Russia (the Caucasus chiefly), and Scotland
are practically the only ones which supply considerable quantities for
use in Great Britain. Attempts are often made to claim superiority for
particular grades of these oils, but it may be at once stated that so for
as actual yield of light is concerned, the same weight of any of the
commercial oils will give practically the same result. Hence in the
comparative statement of the cost of different methods of lighting, oil
will be taken at the cheapest rate at which it could ordinarily be
obtained, including delivery charges, at a country house, when bought by
the barrel. This rate at the present time is about ninepence per gallon.
A higher price may be paid for grades of mineral oil reputed to be safer
or to give a "brighter" or "clearer" light; but as the quantity of light
depends mainly upon the care and attention bestowed on the burner and
glass fittings of the lamp, and partly upon the employment of a suitable
wick, while the safety of each lamp depends at least as much upon the
design of that lamp, and the accuracy with which the wick fits the burner
tube, as upon the temperature at which the oil "flashes," the extra
expense involved in burning fancy-priced oils will not be considered

The efficiency (_i.e._, the light yielded per pint or other unit
volume consumed) of oil-lamps varies greatly, and, speaking broadly,
increases with the power of the lamp. But as large or high-power lamps
are not needed throughout a house, it is fairer to assume that the light
obtainable from oil in ordinary household use is the mean of that
afforded by large and that afforded by small lamps. A large oil-lamp as
commonly used in country houses will give a light of about 20 candle-
power, while a convenient small lamp will give a light of not more than
about 5 candle-power. The large lamp will burn about 55 hours for every
gallon of oil consumed, or give an illuminating duty of about 1100
candle-hours (_i.e._, the product of candle-power by burning-hours)
per gallon. The small lamp, on the other hand, will burn about 140 hours
for every gallon of oil consumed, or give an illuminating duty of about
700 candle-hours per gallon. Actually large lamps would in most country
houses be used only in the entrance hall, living-rooms, and kitchen,
while passages and minor rooms on the lower floors would be lighted by
small lamps. Hence, making due allowance for the lower rate of
consumption of the small lamps, it will be seen that, given equal numbers
of large and small lamps in use, the mean illuminating duty of a gallon
of oil as burnt in country houses will be 987, or, in round figures, 990
candle-hours. Usually candles are used in the bedrooms of country houses
where the lower floors are lighted by means of petroleum lamps; but when
acetylene is installed in such a house it will frequently be adopted in
the principal bed- and dressing-rooms as well as in the living-rooms, as,
unless candles are employed very lavishly, they are really totally
inadequate to meet the reasonable demands for light of, _e.g._, a
lady dressing for dinner. Where acetylene displaces candles as well as
lamps in a country house, it is necessary, in comparing the cost of the
new illuminant with that of the candles and oil, to bear in mind the
superior degree of illumination which is secured in all rooms, at least
where candles were formerly used.

In regard to exhaustion and vitiation of the air, and to heat evolved,
self-luminous petroleum lamps stand on much the same footing as coal-gas
when the latter is burned in flat-flame burners, if the comparison is
based on a given yield of light. A large lamp, owing to its higher
illuminating efficiency, is better in this respect than a small one--
light for light, it is more hygienic than ordinary flat-flame coal-gas
burners, while a small lamp is less hygienic. It will therefore be
understood at once, from what has already been said about the superiority
on hygienic grounds of acetylene to flat-flame coal-gas lighting, that
acetylene is in this respect far superior to petroleum lamps. The degree
of its superiority is indicated more precisely by the figures quoted in
the tabular statement which concludes this chapter.

Before giving the tabular statement, however, it is necessary to say a
few words in regard to one method of lighting which, may possibly develop
into a more serious competitor with acetylene for the lighting of the
better class of country house than any of the illuminating agents and
modes of lighting so far referred to. The method in question is lighting
by so-called air-gas used for raising mantles to incandescence in
upturned or inverted burners of the Welsbach-Kern type. "Air-gas" is
ordinary atmospheric air, more or less completely saturated with the
vapour of some highly volatile hydrocarbon. The hydrocarbons practically
applied have so far been only "petroleum spirit" or "carburine," and
"benzol." "Petroleum spirit" or "carburine" consists of the more highly
volatile portion of petroleum, which is removed by distillation before
the kerosene or burning oil is recovered from the crude oil. Several
grades of this highly volatile petroleum distillate are distinguished in
commerce; they differ in the temperature at which they begin to distil
and the range of temperature covered by their distillation, and, speaking
more generally, in their degree of volatility, uniformity, and density.
If the petroleum distillate is sufficiently volatile and fairly uniform
in character, good air-gas may be produced merely by allowing air to pass
over an extended surface of the liquid. The vapour of the petroleum
spirit is of greater density than air, and hence, if the course of the
air-gas is downward from the apparatus at which it is produced, the flow
of air into the apparatus and over the surface of the spirit will be
automatically maintained by the "pull" of the descending air-gas when
once the flow has been started until the outlet for the air-gas is
stopped or the spirit in the apparatus is exhausted. Hence, if the
apparatus for saturating air with the vapour of the light petroleum is
placed well above all the points at which the air-gas is to be burnt--
_e.g._, on the roof of the house--the production of the air-gas may
by simple devices become automatic, and the only attention the apparatus
will require will be the replenishing of its reservoir from time to time
with light petroleum. But a number of precautions are required to make
this simple process operate without interruption or difficulty. For
instance, the evaporation of the spirit must not be so rapid relatively
to its total bulk as to lower its temperature, and thereby that of the
overflowing air, too much; the reservoir must be protected from extreme
cold and extreme heat; and the risk of fire from the presence of a highly
volatile and highly inflammable liquid on or near the roof of the house
must be met. This risk is one to which fire insurance companies take

More commonly, however, air-gas is made non-automatically, or more or
less automatically by the employment of some mechanical means. The light
petroleum, benzol, or other suitable volatile hydrocarbon is volatilised,
where necessary, by the application of gentle heat, while air is driven
over or through it by means of a small motor, which in some cases is a
hot-air engine operated by heat supplied by a flame of the air-gas
produced. These air-gas producers, or at least the reservoir of volatile
hydrocarbon, may be placed in an outbuilding, so that the risk of fire in
the house itself is minimised. They require, however, as much attention
as an acetylene generator, usually more. It is difficult to give reliable
data as to the cost of air-gas, inclusive of the expenses of production.
It varies considerably with the description of hydrocarbon employed, and
its market price. Air-gas is only slightly inferior hygienically to
acetylene, and the colour of its light is that of the incandescent light
as produced by coal-gas or acetylene. Air-gas of a certain grade may be
used for lighting by flat-flame burners, but it has been available thus
for very many years, and has failed to achieve even moderate success. But
the advent of the incandescent burner has completely changed its position
relatively to most other illuminants, and under certain conditions it
seems likely to be the most formidable competitor with acetylene. Since
air-gas, and the numerous chemically identical products offered under
different proprietary names, is simply atmospheric air more or less
loaded with the vapour of a volatile hydrocarbon which is normally
liquid, it possesses no definite chemical constitution, but varies in
composition according to the design of the generating plant, the
atmospheric temperature at the time of preparation, the original degree
of volatility of the hydrocarbon, the remaining degree of volatility
after the more volatile portions have been vaporised, and the speed at
which the air is passed through the carburettor. The illuminating power
and the calorific value of air-gas, unless the manufacture is very
precisely controlled, are apt to be variable, and the amount of light,
emitted, either in self-luminous or in incandescent burners, is somewhat
indeterminate. The generating plant must be so constructed that the air
cannot at any time be mixed with as much hydrocarbon vapour as
constitutes an explosive mixture with it, otherwise the pipes and
apparatus will contain a gas which will forthwith explode if it is
ignited, _i.e._, if an attempt is made to consume it otherwise than
in burners with specially small orifices. The safely permissible mixtures
are (1) air with less hydrocarbon vapour than constitutes an explosive
mixture, and (2) air with more hydrocarbon vapour than constitutes an
explosive mixture. The first of these two mixtures is available for
illuminating purposes only with incandescent mantles, and to ensure a
reasonable margin of safety the mixing apparatus must be so devised that
the proportion of hydrocarbon vapour in the air-gas can never exceed 2
per cent. From Chapter VI. it will be evident that a little more than 2
per cent. of benzene, pentane or benzoline vapour in air forms an
explosive mixture. What is the lowest proportion of such vapours in
admixture with air which will serve on combustion to maintain a mantle in
a state of incandescence, or even to afford a flame at all, does not
appear to have been precisely determined, but it cannot be much below 1-
1/2 per cent. Hence the apparatus for producing air-gas of this first
class must be provided with controlling or governing devices of such
nicety that the proportion of hydrocarbon vapour in the air-gas is
maintained between about 1-1/2 and 2 per cent. It is fair to say that in
normal working conditions a number of devices appear to fulfil this
requirement satisfactorily. The second of the two mixtures referred to
above, viz., air with more hydrocarbon vapour than constitutes an
explosive mixture, is primarily suitable for combustion in self-luminous
burners, but may also be consumed in properly designed incandescent
burners. But the generating apparatus for such air-gas must be equipped
with some governing or controlling device which will ensure the
proportion of hydrocarbon vapour in the mixture never falling below, say,
7 per cent. On the other hand, if saturation of the air with the vapour
is practically attained, should the temperature of the gas fall before it
arrives at the point of combustion, part of the spirit will condense out,
and the product will thus lose part of its illuminating or calorific
intensity, besides partially filling the pipes with liquid products of
condensation. The loss of intensity in the gas during cold weather may or
may not be inconvenient according to circumstances; but the removal of
part of the combustible material brings the residual air-gas nearer to
its limit of explosibility--for it is simply a mixture of combustible
vapour with air, which, normally, is not explosive because the proportion
of spirit is too high--and thus, when led into an atmospheric burner, the
extra amount of air introduced at the injector jets may cause the mixture
to be an explosive mixture of air and spirit, so that it will take fire
within the burner tube instead of burning quietly at the proper orifice.
This matter will be made clearer on studying what is said about explosive
limits in Chapter VI., and what is stated about incandescent acetylene
(carburetted or not) in Chapters IX. and X. Clearly, however, high-grade
air-gas is only suitable for preparation at the immediate spot where it
is to be consumed; it cannot be supplied to a complete district unless it
is intentionally made of such lower intensity that the proportion of
spirit is too small ever to allow of partial deposition in the mains
during the winter.

It is perhaps necessary to refer to the more extended use of candles for
lighting in some few houses in which lamps are disliked on aesthetic, or,
in some cases, ostensibly on hygienic grounds. Candle lighting, speaking
broadly, is either very inadequate so far as ordinary living-rooms are
concerned, or, if adequate, is very costly. Tests specially carried out
by one of the authors to determine some of the figures required in the
ensuing table show that ordinary paraffin or "wax" candles usually emit
about 20 per cent. more light than that given by the standard spermaceti
candle, whose luminosity is the unit by which the intensity of other
lights is reckoned in Great Britain; and also that the light so emitted
by domestic candles is practically unaffected by the sizes--"sixes,"
"eights," or "twelves"--burnt. In the sizes examined the light evolved
has varied between 1.145 and 1.298 "candles," perhaps tending to increase
slightly with the diameter of the candle tested. Hence, to obtain
illumination in a room equal on the average to that afforded by 100
standard candles, or some other light or lights aggregating 100 candle-
power, would require the use of only 80 to 85 ordinary paraffin,
ozokerite, or wax candles. But actually the essential objects in a room
could be equally well illuminated by, say, 30 candles well distributed,
as by two or three incandescent gas-burners, or four or five large oil-
lamps. Lights of high intensity, such as powerful gas-burners or oil-
lamps, must give a higher degree of illumination in their immediate
vicinity than is really necessary, if they are to illuminate adequately
the more distant objects. The dissemination and diffusion of their light
can be greatly aided by suitable colouring of ceilings, walls and
drapings; but unless the illumination by means of lights of relatively
high intensity is made almost wholly indirect, candles or other lights of
low intensity, such as small electric glow-lamps, can, by proper
distribution, be made to give more uniform or more suitably apportioned
illumination. In this respect candles have an economical and, in some
measure, a material advantage over acetylene also. (But when the method
of lighting is by flames--candle or other--the multiplication of the
number of units which is involved when they are of low intensity,
seriously increases the risk of fire through accidental contact of
inflammable material with any one of the flames. This risk is much
greater with naked flames, such as candles, than with, say, inverted
incandescent gas flames, which are to all intents and purposes fully
protected by a closed glass globe.) Hence, in the tabular statement which
follows of the comparative cost, &c., of different illuminants, it will
be assumed that 30 good candles would in practice be equally efficient in
regard to the illumination of a room as large oil-lamps, acetylene
flames, or incandescent gas-burners aggregating 100 candle-power.

For the same reason it will be assumed that electric glow-lamps of low
intensity (nominally of 8 candle-power or less), aggregating 70-80
candle-power, will practically serve, if suitably distributed, equally as
well as 100 candle-power obtained from more powerful sources of light.
Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
and good flat-flame gas-burners, aggregating 90-95 candle-power, will
similarly be taken as equivalent, if suitably distributed, to 100 candle-
power from more powerful sources of light. Of the latter it will be
assumed that each source has an intensity between 20 and 30 candle-power,
such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
hour acetylene burner. Either of these sources of light, when used in
sufficient numbers, so that with proper distribution they light a room
adequately, will be taken in the tabular statement which follows as
affording, per candle-power evolved, the standard illuminating effect
required in that room. The same illuminating effect will be regarded as
attainable by means of candles aggregating only 35 per cent., or small
electric glow-lamps aggregating 77 per cent., or large electric glow-
lamps and flat-flame gas-burners aggregating 90 to 95 per cent. of this
candle-power; while if sources of light of higher intensity are used,
such as Osram or Tantalum electric lamps, or the larger incandescent gas-
burners (the Welsbach "C" or "York," or the Nos. 3 or 4 Welsbach-Kern
upturned, or the No. 1 or larger size inverted burners) or incandescent
acetylene burners, it will be assumed that their aggregate candle-power
must be in excess by about 15 per cent., in order to compensate for the
impossibility of obtaining equally well distributed illumination. These
assumptions are based on general considerations and data as to the effect
of sources of light of different intensities in giving practically the
same degree of illumination in a room; it would occupy too much space
here to discuss more fully the grounds on which they have been made. It
must suffice to say that they have been adopted with the object of being
perfectly fair to each means of illumination.


The data (except in the column headed "cost per 100 candle-hours") refer
to the illumination afforded by medium-sized (0.5 to 0.7 cubic foot per
hour) acetylene burners yielding together a light of about 100 candle-
power, and to the approximately equivalent illumination as afforded by
other means of illumination, when the lighting-units or sources of light
are rationally distributed.

Interest and depreciation charges on the outlay on piping or wiring a
house, on brackets, fittings, lamps, candelabra, and storage
accommodation (for carbide and oil) have been taken as equivalent for all
modes of lighting, and omitted in computing the total cost. The cost of
labour for attendance on acetylene plant, oil lamps, and candles is an
uncertain and variable item--approximately equal for all these modes of
lighting, but saved in coal-gas and electric lighting from public supply

| | | | | | |
| | |Candle- | Number |Aggregate| Cost |
| | |Power of| of | Candle- | per |
| | Description of | each |Lighting | Power | 100 |
|Illuminant. | Burner or Lamp. |Lighting| Units |Afforded.|Candle-|
| | | Unit. |Required.|(About.) |Hours. |
| | |(About.)| | |Pence. |
| | | | | | |
| |Self-luminous; 0.5 | | | | |
| | cubic foot per hour| 18 | 5 | 90 | 1.11 |
| |Self-luminous; 0.7 | | | | |
| Acetylene | cubic foot per hour| 27 | 4 | 108 | 1.02 |
| |Self-luminous; 1.0 | | | | |
| | cubic foot per hour| 45.5 | 3 | 136 | 0.85 |
| |Incandescent; 0.5 | | | | |
| | cubic foot per hour| 50 | 3 | 150 | 0.49 |
| | | | | | |
| Petroleum | Large lamp . . . . | 20 | 5 | 100 | 0.84 |
| (paraffin | | | | | |
| oil) | Small lamp . . . . | 5 | 14 | 70 | 1.31 |
| | | | | | |
| |Flat flame (bad) 5 | | | | |
| | cubic feet per hour| 8 | 10 | 80 | 3.75 |
| |Flat flame (good) 6 | | | | |
| Coal Gas | cubic feet per hour| 16 | 6 | 96 | 2.25 |
| |Incandescent (No. 1 | | | | |
| | Kern or Bijou In- | 25 | 4 | 100 | 0.38 |
| | verted); 1-1/2 | | | | |
| | cubic feet per hour| | | | |
| | | | | | |
| Candles |"Wax" (so-called) . | 1.2 | 30 | 35 | 6.14 |
| | | | | | |
| | Small glow . . . . | 7 | 11 | 77 | 2.81 |
| | Large glow . . . . | 13 | 7 | 91 | 2.90 |
| Electricity| | | | | |
| | Tantalum . . . . . | 19 | 5 | 95 | 1.52 |
| | Osram . . . . . . | 14 | 7 | 98 | 1.00 |

| | | | |
| | | | |
| | | | Equivalent |
| | Description of | Assumed Cost | Illumin- |
|Illuminant. | Burner or Lamp. | of Illuminant. | ation. |
| | | | Pence. |
| | | | |
| | | | |
| |Self-luminous; 0.5 | Calcium carbide | |
| | cubic foot per hour| (yielding 5 | 1.00 |
| |Self-luminous; 0.7 | cubic feet of | |
| Acetylene | cubic foot per hour| acetylene per | 1.10 |
| |Self-luminous; 1.0 | lb.) at 15s. | |
| | cubic foot per hour| per cwt., inclu- | 1.16 |
| |Incandescent; 0.5 | ding delivery | |
| | cubic foot per hour| charges. | 0.74 |
| | | | |
| Petroleum | Large lamp . . . . | Oil, 9d. per gal- | 0.84 |
| (paraffin | | lon, including | |
| oil) | Small lamp . . . . | delivery charges. | 0.92 |
| | | | |
| |Flat flame (bad) 5 | | |
| | cubic feet per hour| Public supply | 3.00 |
| |Flat flame (good) 6 | from small | |
| Coal Gas | cubic feet per hour| country works, | 2.16 |
| |Incandescent (No. 1 | at 5s. per 1000 | |
| | Kern or Bijou In- | cubic feet. | 0.38 |
| | verted); 1-1/2 | | |
| | cubic feet per hour| | |
| | | | |
| Candles |"Wax" (so-called) . | 5d. per lb. | 2.60 |
| | | | |
| | Small glow . . . . | Public supply | 2.16 |
| | Large glow . . . . | from small | 2.64 |
| Electricity| | town works | |
| | Tantalum . . . . . | at 6d. per | 1.45 |
| | Osram . . . . . . | B.O.T. unit. | 0.98 |

| | | | | | |
| | |Inci- | Exhaus- |Vitiation | Heat |
| | | den- | tion of | of Air. |Produced.|
| | Description of | tal |Air.Cubic|Cubic Feet|Number of|
|Illuminant. | Burner or Lamp. |Expen-|Feet Dep-| of Car- |Units of |
| | | ces. |rived of |bonic Acid| Heat. |
| | | | Oxygen. | Formed. |Calories.|
| | | | | | |
| |Self-luminous; 0.5 | | | | |
| | cubic foot per hour| [1] | 29.8 | 5.0 | 900 |
| |Self-luminous; 0.7 | | | | |
| Acetylene | cubic foot per hour| | 33.3 | 5.6 | 1010 |
| |Self-luminous; 1.0 | | | | |
| | cubic foot per hour| | 35.7 | 6.0 | 1000 |
| |Incandescent; 0.5 | | | | |
| | cubic foot per hour| [2] | 17.9 | 3.0 | 545 |
| | | | | | |
| Petroleum | Large lamp . . . . | | 140.0 | 19.6 | 3630 |
| (paraffin | | [3] | | | |
| oil) | Small lamp . . . . | | 154.0 | 21.6 | 4000 |
| | | | | | |
| |Flat flame (bad) 5 | | | | |
| | cubic feet per hour| Nil | 270.0 | 27.0 | 7750 |
| |Flat flame (good) 6 | | | | |
| Coal Gas | cubic feet per hour| Nil | 195.0 | 19.5 | 5580 |
| |Incandescent (No. 1 | | | | |
| | Kern or Bijou In- | [4] | 27.0 | 2.7 | 775 |
| | verted); 1-1/2 | | | | |
| | cubic feet per hour| | | | |
| | | | | | |
| Candles |"Wax" (so-called) . | Nil | 100.5 | 13.7 | 2700 |
| | | | | | |
| | Small glow . . . . |2s.6d.| Nil | Nil | 285 |
| | Large glow . . . . |2s.6d.| " | " | 360 |
| Electricity| | [5] | | | |
| | Tantalum . . . . . |7s.6d.| " | " | 172 |
| | Osram . . . . . . | 6s. | " | " | 96 |

[Footnote 1: Interest and depreciation charges on generating and
purifying plant = 0.15 penny. Purifying material and burner renewals =
0.05 penny.]

[Footnote 2: Mantle renewals as for coal-gas.]

[Footnote 3: Renewals of wicks and chimneys = 0.02 penny.]

[Footnote 4: Renewals and mantles (and chimneys) at contract rate of 3s.
per burner per annum.]

[Footnote 5: Renewals of lamps and fuses, at price indicated per lamp per

The conventional method of making pecuniary comparisons between different
sources of artificial light consists in simply calculating the cost of
developing a certain number of candle-hours of light--_i.e._, a
certain amount of standard candle-power for a given number of hours--on
the assumption that as many separate sources of light are employed as may
be required to bring the combined illuminating power up to the total
amount wanted. In view of the facts as to dissemination and diffusion, or
the difference between sheer illuminating power and useful illuminating
effect, which have just been elaborated, and in view of the different
intensities of the different unit sources of light (which range from the
single candle to a powerful large incandescent gas-burner or a metallic
filament electric lamp), such a method of calculation is wholly illusory.
The plan adopted in the following table may also appear unnecessarily
complicated; but it is not so to the reader if he remembers that the
apparently various amount of illumination is corrected by the different
numbers of illuminating units until the amount of simple candle-power
developed, whatever illuminant be employed, suffices to light a room
having an area of about 300 square feet (_i.e._, a room, 17-1/2 feet
square, or one 20 feet long by 15 feet wide), so that ordinary print may
be read comfortably in any part of the room, and the titles of books,
engravings, &c., in any position on the walls up to a height of 8 feet
from the ground may be distinguished with ease. The difference in cost,
&c., of a greater or less degree of illumination, or of lighting a larger
or smaller room by acetylene or any other of the illuminants named, will
be almost directly proportional to the cost given for the stated
conditions. Nevertheless, it should be recollected that when the
conventional system is retained--useful illuminating effect being
sacrificed to absolute illuminating power--acetylene is made to appear
cheaper in comparison with all weaker unit sources of light, and dearer
in comparison with all stronger unit sources of light than the
accompanying table indicates it to be. In using the comparative figures
given in the table, it should be borne in mind that they refer to more
general and more brilliant illumination of a room than is commonly in
vogue where the lighting is by means of electric light, candles, or oil-
lamps. The standard of illumination adopted for the table is one which is
only gaining general recognition where incandescent gas or acetylene
lighting is available, though in exceptional cases it has doubtless been
attained by means of oil-lamps or flat-flame gas-burners, but very rarely
if ever by means of carbon-filament electric glow-lamps, or candles. It
assumes that the occupants of a room do not wish to be troubled to bring
work or book "to the light," but wish to be able to work or read
wheresoever in the room they will, without consideration of the
whereabouts of the light or lights.

It should, perhaps, be added that so high a price as 5s. per 1000
cubic feet for coal-gas rarely prevails in Great Britain, except in small
outlying towns, whereas the price of 6d. per Board of Trade unit
for electricity is not uncommonly exceeded in the few similar country
places in which there is a public electricity supply.



THE NATURE OF CALCIUM CARBIDE.--The raw material from which, by
interaction with water, acetylene is obtained, is a solid body called
calcium carbide or carbide of calcium. Inasmuch as this substance can at
present only be made on a commercial scale in the electric furnace--and
so far as may be foreseen will never be made on a large scale except by
means of electricity--inasmuch as an electric furnace can only be worked
remuneratively in large factories supplied with cheap coal or water
power; and inasmuch as there is no possibility of the ordinary consumer
of acetylene ever being able to prepare his own carbide, all descriptions
of this latter substance, all methods of winning it, and all its
properties except those which concern the acetylene-generator builder or
the gas consumer have been omitted from the present book. Hitherto
calcium carbide has found but few applications beyond that of evolving
acetylene on treatment with water or some aqueous liquid, hygroscopic
solid, or salt containing water of crystallisation; but it has
possibilities of further employment, should its price become suitable,
and a few words will be devoted to this branch of the subject in Chapter
XII. Setting these minor uses aside, calcium carbide has no intrinsic
value except as a producer of acetylene, and therefore all its
characteristics which interest the consumer of acetylene are developed
incidentally throughout this volume as the necessity for dealing with
them arises.

It is desirable, however, now to discuss one point connected with solid
carbide about which some misconception prevails. Calcium carbide is a
body which evolves an inflammable, or on occasion an explosive, gas when
treated with water; and therefore its presence in a building has been
said to cause a sensible increase in the fire risk because attempts to
extinguish a fire in the ordinary manner with water may cause evolution
of acetylene which should determine a further production of flame and
heat. In the absence of water, calcium carbide is absolutely inert as
regards fire; and on several occasions drums of it have been recovered
uninjured from the basement of a house which has been totally destroyed
by fire. With the exception of small 1-lb. tins of carbide, used only by
cyclists, &c., the material is always put into drums of stout sheet-iron
with riveted or folded seams. Provided the original lid has not been
removed, the drums are air- and water-tight, so that the fireman's hose
may be directed upon them with impunity. When a drum has once been
opened, and not all of its contents have been put into the generator,
ordinary caution--not merely as regards fire, but as regards the
deterioration of carbide when exposed to the atmosphere--suggests either
that the lid must be made air-tight again (not by soldering it),
[Footnote: Carbide drums are not uncommonly fitted with self-sealing or
lever-top lids, which are readily replaced hermetically tight after
opening and partial removal of the contents of the drum.] or preferably
that the rest of the carbide shall be transferred to some convenient
receptacle which can be perfectly closed. [Footnote: It would be a
refinement of caution, though hardly necessary in practice, to fit such a
receptacle with a safety-valve. If then the vessel were subjected to
sudden or severe heating, the expansion of the air and acetylene in it
could not possibly exert a disruptive effect upon the walls of the
receptacle, which, in the absence of the safety-valve, is imaginable.]
Now, assuming this done, the drums are not dependent upon soft solder to
keep them sound, and so they cannot open with heat. Fire and water,
accordingly, cannot affect them, and only two risks remain: if stored in
the basement of a tall building, falling girders, beams or brickwork may
burst them; or if stored on an upper floor, they may fall into the
basement and be burst with the shock--in either event water then having
free access to the contents. But drums of carbide would never be stored
in such positions: a single one would be kept in the generator-house;
several would be stored in a separate room therein, or in some similar
isolated shed. The generator-house or shed would be of one story only;
the drums could neither fall nor have heavy weights fall on them during a
fire; and therefore there is no reason why, if a fire should occur, the
firemen should not be permitted to use their hose in the ordinary
fashion. Very similar remarks apply to an active acetylene generator.
Well built, such plant will stand much heat and fire without failure; if
it is non-automatic, and of combustible materials contains nothing but
gas in the holder, the worst that could happen in times of fire would be
the unsealing of the bell or its fracture, and this would be followed,
not at all by any explosion, but by a fairly quiet burning of the
escaping gas, which would be over in a very short time, and would not add
to the severity of the conflagration unless the generator-house were so
close to the residence that the large flame of burning gas could ignite
part of the main building. Even if the heat were so great near the holder
that the gas dissociated, it is scarcely conceivable that a dangerous
explosion should arise. But it is well to remember, that if the
generator-house is properly isolated from the residence, if it is
constructed of non-inflammable materials, if the attendant obeys
instructions and refrains from taking a naked light into the
neighbourhood of the plant, and if the plant itself is properly designed
and constructed, a fire at or near an acetylene generator is extremely
unlikely to occur. At the same time, before the erection of plant to
supply any insured premises is undertaken, the policy or the company
should be consulted to ascertain whether the adoption of acetylene
lighting is possibly still regarded by the insurers as adding an extra
risk or even as vitiating the whole insurance.

regulations imposed by many local authorities respecting the storage of
carbide, and usually a licence for storage has to be obtained if more
than 5 lb. is kept at a time. The idea of the rule is perfectly
justifiable, and it is generally enforced in a sensible spirit. As the
rules may vary in different localities, the intending consumer of
acetylene must make the necessary inquiries, for failure to comply with
the regulations may obviously be followed by unpleasantness.

Having regard to the fact that, in virtue of an Order in Council dated
July 7, 1897, carbide may be stored without a licence only in separate
substantial hermetically closed metal vessels containing not more than 1
lb. apiece and in quantities not exceeding 5 lb. in the aggregate, and
having regard also to the fact that regulations are issued by local
authorities, the Fire Offices' Committee of the United Kingdom has not up
to the present deemed it necessary to issue special rules with reference
to the storage of carbide of calcium.

The following is a copy of the rules issued by the National Board of Fire
Underwriters of the UNITED STATES OF AMERICA for the storage of calcium
carbide on insured premises:


(_a_) Calcium carbide in quantities not to exceed six hundred (600)
pounds may be stored, when contained in approved metal packages not to
exceed one hundred (100) pounds each, inside insured property, provided
that the place of storage be dry, waterproof and well ventilated, and
also provided that all but one of the packages in any one building shall
be sealed and the seals shall not be broken so long as there is carbide
in excess of one (1) pound in any other unsealed package in the building.

(_b_) Calcium carbide in quantities in excess of six hundred (600)
pounds must be stored above ground in detached buildings, used
exclusively for the storage of calcium carbide, in approved metal
packages, and such buildings shall be constructed to be dry, waterproof
and well ventilated.

(_c_) Packages to be approved must be made of metal of sufficient
strength to insure handling the package without rupture, and be provided
with a screwed top or its equivalent.

They must be constructed so as to be water- and air-tight without the use
of solder, and conspicuously marked "CALCIUM CARBIDE--DANGEROUS IF NOT

The following is a summary of the AUSTRIAN GOVERNMENT rules relating to
the storage and handling of carbide:

(1) It must be sold and stored only in closed water-tight vessels, which,
if the contents exceed 10 kilos., must be marked in plain letters
"CALCIUM CARBIDE--TO BE KEPT CLOSED AND DRY." They must not be of copper
and if soldered must be opened by mechanical means and not by
unsoldering. They must be stored out of the reach of water.

(2) Quantities not exceeding 300 kilos. may be stored in occupied houses,
provided the single drums do not exceed 100 kilos. nominal capacity. The
storage-place must be dry and not underground.

(3) The limits specified in Rule 2 apply also to generator-rooms, with
the proviso also that in general the amount stored shall not exceed five
days' consumption.

(4) Quantities ranging from 300 to 1000 kilos. must be stored in special
well-ventilated uninhabited non-basement rooms in which lights and
smoking are not allowed.

(5) Quantities exceeding 1000 kilos. must be stored in isolated fireproof
magazines with light water-tight roofs. The floors must be at least 8
inches above ground-level.

(6) Carbide in water-tight drums may be stored in the open in a fenced
enclosure at least 30 feet from buildings, adjoining property, or
inflammable materials. The drums must be protected from wet by a light

(7) The breaking of carbide must be done by men provided with respirators
and goggles, and care taken to avoid the formation of dust.

(8) Local or other authorities will issue from time to time special
regulations in regard to carbide trade premises.

The ITALIAN GOVERNMENT rules relating to the storage and transport of
carbide follow in the main those of the Austrian Government, but for
quantities between 300 and 2000 kilos sanction is required from the local
authorities, and for larger quantities from superior authorities. The
storage of quantities ranging from 300 to 2000 kilos is forbidden in
dwelling-houses and above the latter quantity the storage-place must be
isolated and specially selected. No special permit is required for the
storage of quantities not exceeding 300 kilos. Workmen exposed to carbide
dust arising from the breaking of carbide or otherwise must have their
eyes and respiratory organs suitably protected.

THE PURCHASE OF CARBIDE.--Since calcium carbide is only useful as a means
of preparing acetylene, it should be bought under a guarantee (1) that it
contains less impurities than suffice to render the crude gas dangerous
in respect of spontaneous inflammability, or objectionable in a manner to
be explained later on, when consumed; and (2) that it is capable of
evolving a fixed minimum quantity of acetylene when decomposed by water.
Such determination, however, cannot be carried out by the ordinary
consumer for himself. A generator which is perfectly satisfactory in
general behaviour, and which evolves a sufficient proportion of the
possible total make of gas to be economical, does not of necessity
decompose the carbide quantitatively; nor is it constructed in a fashion
to render an exact measurement of the gas liberated at standard
temperature and pressure easy to obtain. For obvious reasons the careful
consumer of acetylene will keep a record of the carbide decomposed and of
the acetylene generated--the latter perhaps only in terms of burner-
hours, or the like; but in the event of serious dispute as to the gas-
making capacity of his raw material, he must have a proper analysis made
by a qualified chemist.

Calcium carbide is crushed by the makers into several different sizes, in
each of which all the lumps exceed a certain size and are smaller than
another size. It is necessary to find out by experiment, or from the
maker, what particular size suits the generator best, for different types
of apparatus require different sizes of carbide. Carbide cannot well be
crushed by the consumer of acetylene. It is a difficult operation, and
fraught with the production of dust which is harmful to the eyes and
throat, and if done in open vessels the carbide deteriorates in gas-
making power by its exposure to the moisture of the atmosphere. True dust
in carbide is objectionable, and practically useless for the generation
of acetylene in any form of apparatus, but carbide exceeding 1 inch in
mesh is usually sold to satisfy the suggestions of the British Acetylene
Association, which prescribes 5 per cent, of dust as the maximum. Some
grades of carbide are softer than others, and therefore tend to yield
more dust if exposed to a long journey with frequent unloadings.

There are certain varieties of ordinary carbide known as "treated
carbide," the value of which is more particularly discussed in Chapter
III. The treatment is of two kinds, or of a combination of both. In one
process the lumps are coated with a strong solution of glucose, with the
object of assisting in the removal of spent lime from their surface when
the carbide is immersed in water. Lime is comparatively much more soluble
in solutions of sugar (to which class of substances glucose belongs) than
in plain water; so that carbide treated with glucose is not so likely to
be covered with a closely adherent skin of spent lime when decomposed by
the addition of water to it. In the other process, the carbide is coated
with or immersed in some oil or grease to protect it from premature
decomposition. The latter idea, at least, fulfils its promises, and does
keep the carbide to a large extent unchanged if the lumps are exposed to
damp air, while solving certain troubles otherwise met with in some
generators (cf. Chapter III.); but both operations involve additional
expense, and since ordinary carbide can be used satisfactorily in a good
fixed generator, and can be preserved without serious deterioration by
the exercise of reasonable care, treated carbide is only to be
recommended for employment in holderless generators, of which table-lamps
are the most conspicuous forms. A third variant of plain carbide is
occasionally heard of, which is termed "scented" carbide. It is difficult
to regard this material seriously. In all probability calcium carbide is
odourless, but as it begins to evolve traces of gas immediately
atmospheric moisture reaches it, a lump of carbide has always the
unpleasant smell of crude acetylene. As the material is not to be stored
in occupied rooms, and as all odour is lost to the senses directly the
carbide is put into the generator, scented carbide may be said to be
devoid of all utility.

THE REACTION BETWEEN CARBIDE AND WATER.--The reaction which occurs when
calcium carbide and water are brought into contact belongs to the class
that chemists usually term double decompositions. Calcium carbide is a
chemical compound of the metal calcium with carbon, containing one
chemical "part," or atomic weight, of the former united to two chemical
parts, or atomic weights, of the latter; its composition expressed in
symbols being CaC_2. Similarly, water is a compound of two chemical parts
of hydrogen with one of oxygen, its formula being H_2O. When those two
substances are mixed together the hydrogen of the water leaves its
original partner, oxygen, and the carbon of the calcium carbide leaves
the calcium, uniting together to form that particular compound of
hydrogen and carbon, or hydrocarbon, which is known as acetylene, whose
formula is C_2H_2; while the residual calcium and oxygen join together to
produce calcium oxide or lime, CaO. Put into the usual form of an
equation, the reaction proceeds thus--

(1) CaC_2 + H_2O = C_2H_2 + CaO.

This equation not only means that calcium carbide and water combine to
yield acetylene and lime, it also means that one chemical part of carbide
reacts with one chemical part of water to produce one chemical part of
acetylene and one of lime. But these four chemical parts, or molecules,
which are all equal chemically, are not equal in weight; although,
according to a common law of chemistry, they each bear a fixed proportion
to one another. Reference to the table of "Atomic Weights" contained in
any text-book of chemistry will show that while the symbol Ca is used,
for convenience, as a contraction or sign for the element calcium simply,
it bears a more important quantitative significance, for to it will be
found assigned the number 40. Against carbon will be seen the number 12;
against oxygen, 16; and against hydrogen, 1. These numbers indicate that
if the smallest weight of hydrogen ever found in a chemical compound is
called 1 as a unit of comparison, the smallest weights of calcium,
carbon, and oxygen, similarly taking part in chemical reactions are 40,
12, and 16 respectively. Thus the symbol CaC_2, comes to convoy three
separate ideas: (_a_) that the substance referred to is a compound
of calcium and carbon only, and that it is therefore a carbide of
calcium; (_b_) that it is composed of one chemical part or atom of
calcium and two atoms of carbon; and (_c_) that it contains 40 parts
by weight of calcium combined with twice twelve, or 24, parts of carbon.
It follows from (_c_) that the weight of one chemical part, now
termed a molecule as the substance is a compound, of calcium carbide is
(40 + 2 x 12) = 64. By identical methods of calculation it will be found
that the weight of one molecule of water is 18; that of acetylene, 26;
and that of lime, 56. The general equation (1) given above, therefore,
states in chemical shorthand that 64 parts by weight of calcium carbide
react with 18 parts of water to give 26 parts by weight of acetylene and
56 parts of lime; and it is very important to observe that just as there
are the same number of chemical parts, viz., 2, on each side, so there
are the same number of parts by weight, for 64 + 18 = 56 + 26 = 82. Put
into other words equation (1) shows that if 64 grammes, lb., or cwts. of
calcium carbide are treated with 18 grammes, lb., or cwts. of water, the
whole mass will be converted into acetylene and lime, and the residue
will not contain any unaltered calcium carbide or any water; whence it
may be inferred, as is the fact, that if the weights of carbide and water
originally taken do not stand to one another in the ratio 64 : 18, both
substances cannot be entirely decomposed, but a certain quantity of the
one which was in excess will be left unattacked, and that quantity will
be in exact accordance with the amount of the said excess--indifferently
whether the superabundant substance be carbide or water.

Hitherto, for the sake of simplicity, the by-product in the preparation
of acetylene has been described as calcium oxide or quicklime. It is,
however, one of the leading characteristics of this body to be
hygroscopic, or greedy of moisture; so that if it is brought into the
presence of water, either in the form of liquid or as vapour, it
immediately combines therewith to yield calcium hydroxide, or slaked
lime, whose chemical formula is Ca(OH)_2. Accordingly, in actual
practice, when calcium carbide is mixed with an excess of water, a
secondary reaction takes place over and above that indicated by equation
(1), the quicklime produced combining with one chemical part or molecule
of water, thus--

CaO + H_2O = Ca(OH)_2.

As these two actions occur simultaneously, it is more usual, and more in
agreement with the phenomena of an acetylene generator, to represent the
decomposition of calcium carbide by the combined equation--

(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2.

By the aid of calculations analogous to those employed in the preceding
paragraph, it will be noticed that equation (2) states that 1 molecule of
calcium carbide, or 64 parts by weight, combines with 2 molecules of
water, or 36 parts by weight, to yield 1 molecule, or 26 parts by weight
of acetylene, and 1 molecule, or 74 parts by weight of calcium hydroxide
(slaked lime). Here again, if more than 36 parts of water are taken for
every 64 parts of calcium carbide, the excess of water over those 36
parts is left undecomposed; and in the same fashion, if less than 36
parts of water are taken for every 64 parts of calcium carbide, some of
the latter must remain unattacked, whilst, obviously, the amount of
acetylene liberated cannot exceed that which corresponds with the
quantity of substance suffering complete decomposition. If, for example,
the quantity of water present in a generator is more than chemically
sufficient to attack all the carbide added, however largo or small that
excess may be, no more, and, theoretically speaking, no less, acetylene
can ever be evolved than 26 parts by weight of gas for every 64 parts by
weight of calcium carbide consumed. It is, however, not correct to invert
the proposition, and to say that if the carbide is in excess of the water
added, no more, and, theoretically speaking, no less, acetylene can ever
be evolved than 26 parts by weight of gas for every 36 parts of water
consumed, as might be gathered from equation (2); because equation (1)
shows that 26 parts of acetylene may, on occasion, be produced by the
decomposition of 18 parts by weight of water. From the purely chemical
point of view this apparent anomaly is explained by the circumstance that
of the 36 parts of water present on the left-hand aide of equation (2),
only one-half, _i.e._, 18 parts by weight, are actually decomposed
into hydrogen and oxygen, the other 18 parts remaining unattacked, and
merely attaching themselves as "water of hydration" to the 56 parts of
calcium oxide in equation (1) so as to produce the 74 parts of calcium
hydroxide appearing on the right-hand side of equation (2). The matter is
perhaps rendered more intelligible by employing the old name for calcium
hydroxide or slaked lime, viz., hydrated oxide of calcium, and by writing
its formula in the corresponding form, when equation (2) becomes

CaC_2 + 2H_2O = C_2H_2 + CaO.H_2O.

It is, therefore, absolutely correct to state that if the amount of
calcium carbide present in an acetylene generator is more than chemically
sufficient to decompose all the water introduced, no more, and
theoretically speaking no less, acetylene can ever be liberated than 26
parts by weight of gas for every 18 parts by weight of water attacked.
This, it must be distinctly understood, is the condition of affairs
obtaining in the ideal acetylene generator only; since, for reasons which
will be immediately explained, when the output of gas is measured in
terms of the water decomposed, in no commercial apparatus, and indeed in
no generator which can be imagined fit for actual employment, does that
output of gas ever approach the quantitative amount; but the volume of
water used, if not actually disappearing, is always vastly in excess of
the requirements of equation (2). On the contrary, when the make of gas
is measured in terms of the calcium carbide consumed, the said make may,
and frequently does, reach 80, 90, or even 99 per cent. of what is
theoretically possible. Inasmuch as calcium carbide is the one costly
ingredient in the manufacture of acetylene, so long as it is not wasted--
so long, that is to say, as nearly the theoretical yield of gas is
obtained from it--an acetylene generator is satisfactory or efficient in
this particular; and except for the matter of solubility discussed in the
following chapter, the quantity of water consumed is of no importance

HEAT EVOLVED IN THE REACTION.--The chemical reaction between calcium
carbide and water is accompanied by a large evolution of heat, which,
unless due precautions are taken to prevent it, raises the temperature of
the substances employed, and of the apparatus containing them, to a
serious and often inconvenient extent. This phenomenon is the most
important of all in connexion with acetylene manufacture; for upon a
proper recognition of it, and upon the character of the precautions taken
to avoid its numerous evil effects, depend the actual value and capacity
for smooth working of any acetylene generator. Just as, by an immutable
law of chemistry, a given weight of calcium carbide yields a given weight
of acetylene, and by no amount of ingenuity can be made to produce either
more or less; so, by an equally immutable law of physics, the
decomposition of a given weight of calcium carbide by water, or the
decomposition of a given weight of water by calcium carbide, yields a
perfectly definite quantity of heat--a quantity of heat which cannot be
reduced or increased by any artifice whatever. The result of a production
of heat is usually to raise the temperature of the material in which it
is produced; but this is not always the case, and indeed there is no
necessary connexion or ratio between the quantity of heat liberated in
any form of chemical reaction--of which ordinary combustion is the
commonest type--and the temperature attained by the substances concerned.
This matter has so weighty a bearing upon acetylene generation, and
appears to be so frequently misunderstood, that a couple of illustrations
may with advantage be studied. If a vessel full of cold water, and
containing also a thermometer, is placed over a lighted gas-burner, at
first the temperature of the liquid rises steadily, and there is clearly
a ratio between the size of the flame and the speed at which the mercury
mounts up the scale. Finally, however, the thermometer indicates a
certain point, viz., 100 deg. C, and the water begins to boil; yet although
the burner is untouched, and consequently, although heat must be passing
into the vessel at the same rate as before, the mercury refuses to move
as long as any liquid water is left. By the use of a gas meter it might
be shown that the same volume of gas is always consumed (_a_) in
raising the temperature of a given quantity of cold water to the boiling-
point, and another equally constant volume of gas is always consumed
(_b_) in causing the boiling water to disappear as steam. Hence, as
coal-gas is assumed for the present purpose to possess invariably the
same heating power, it appears that the same quantity of heat is always
needed to convert a given amount of cold water at a certain temperature
into steam; but inasmuch as reference to the meter would show that about
5 times the volume of gas is consumed in changing the boiling water into
steam as is used in heating the cold water to the boiling-point, it will
be evident that the temperature of the mass is raised as high by the heat
evolved during the combustion of one part of gas as it is by that
liberated on the combustion of 6 times that amount.

A further example of the difference between quantity of heat and sensible
temperature may be seen in the combustion of coal, for (say) one
hundredweight of that fuel might be consumed in a very few minutes in a
furnace fitted with a powerful blast of air, the operation might be
spread over a considerable number of hours in a domestic grate, or the
coal might be allowed to oxidise by exposure to warm air for a year or
more. In the last case the temperature might not attain that of boiling
water, in the second it would be about that of dull redness, and in the
first it would be that of dazzling whiteness; but in all three cases the
total quantity of heat produced by the time the coal was entirely
consumed would be absolutely identical. The former experiment with water
and a gas-burner, too, might easily be modified to throw light upon
another problem in acetylene generation, for it would be found that if
almost any other liquid than water were taken, less gas (_i.e._, a
smaller quantity of heat) would be required to raise a given weight of it
from a certain low to a certain high temperature than in the case of
water itself; while if it were possible similarly to treat the same
weight of iron (of which acetylene generators are constructed), or of
calcium carbide, the quantity of heat used to raise it through a given
number of thermometric degrees would hardly exceed one-tenth or one-
quarter of that needed by water itself. In technical language this
difference is due to the different specific heats of the substances
mentioned; the specific heat of a body being the relative quantity of
heat consumed in raising a certain weight of it a certain number of
degrees when the quantity of heat needed to produce the same effect on
the same weight of water is called unity. Thus, the specific heat of
water being termed 1.0, that of iron or steel is 0.1138, and that of
calcium carbide 0.247, [Footnote: This is Carlson's figure. Morel has
taken the value 0.103 in certain calculations.] both measured at
temperatures where water is a liquid. Putting the foregoing facts in
another shape, for a given rise in temperature that substance will absorb
the most heat which has the highest specific heat, and therefore, in this
respect, 1 part by weight of water will do the work of roughly 9 parts by
weight of iron, and of about 4 parts by weight of calcium carbide.

From the practical aspect what has been said amounts to this: During the
operation of an acetylene generator a large amount of heat is produced,
the quantity of which is beyond human control. It is desirable, for
various reasons, that the temperature shall be kept as low as possible.
There are three substances present to which the heat may be compelled to
transfer itself until it has opportunity to pass into the surrounding
atmosphere: the material of which the apparatus is constructed, the gas
which is in process of evolution, and whichever of the two bodies--
calcium carbide or water--is in excess in the generator. Of these, the
specific heat at constant pressure of acetylene has unfortunately not yet
been determined, but its relative capacity for absorbing heat is
undoubtedly small; moreover the gas could not be permitted to become
sufficiently hot to carry off the heat without grave disadvantages. The
specific heat of calcium carbide is also comparatively small, and there
are similar disadvantages in allowing it to become hot; moreover it is
deficient in heat-conducting power, so that heat communicated to one
portion of the mass does not extend rapidly throughout, but remains
concentrated in one spot, causing the temperature to rise objectionably.
Steel has a sufficient amount of heat-conducting power to prevent undue
concentration in one place; but, as has been stated, its specific heat is
only one-ninth that of water. Water is clearly, therefore, the proper
substance to employ for the dissipation of the heat generated, although
it is strictly speaking almost devoid of heat-conducting power; for not
only is the specific heat of water much greater than that of any other
material present, but it possesses in a high degree the faculty of
absorbing heat throughout its mass, by virtue of the action known as
convection, provided that heat is communicated to it at or near the
bottom, and not too near its upper surface. Moreover, water is a much
more valuable substance for dissipating heat than appears from the
foregoing explanation; for reference to the experiment with the gas-
burner will show that six and a quarter times as much heat can be
absorbed by a given weight of water if it is permitted to change into
steam, as if it is merely raised to the boiling-point; and since by no
urging of the gas-burner can the temperature be raised above 100 deg. C. as
long as any liquid water remains unevaporated, if an excess of water is
employed in an acetylene generator, the temperature inside can never--
except quite locally--exceed 100 deg. C., however fast the carbide be
decomposed. An indefinitely large consumption of water by evaporation in
a generator matters nothing, for the liquid may be considered of no
pecuniary value, and it can all be recovered by condensation in a
subsequent portion of the plant.

It has been said that the quantity of heat liberated when a certain
amount of carbide suffers decomposition is fixed; it remains now to
consider what that quantity is. Quantities of heat are always measured in
terms of the amount needed to raise a certain weight of water a certain
number of degrees on the thermometric scale. There are several units in
use, but the one which will be employed throughout this book is the
"Large Calorie"; a large calorie being the amount of heat absorbed in
raising 1 kilogramme of water 1 deg. C. Referring for a moment to what has
been said about specific heats, it will be apparent that if 1 large
calorie is sufficient to heat 1 kilo, of water through 1 deg. C. the same
quantity will heat 1 kilo. of steel, whose specific heat is roughly 0.11,
through (10/011) = 9 deg. C., or, which comes to the same thing, will heat 9
kilos, of steel through 1 deg. C.; and similarly, 1 large calorie will raise
4 kilos. of calcium carbide 1 deg. C. in temperature, or 1 kilo. 4 deg. C.
The fact that a definite quantity of heat is manifested when a known weight
of calcium carbide is decomposed by water is only typical; for in every
chemical process some disturbance of heat, though not necessarily of
sensible (or thermometric) character, occurs, heat being either absorbed
or set free. Moreover, if when given weights of two or more substances
unite to form a given weight of another substance, a certain quantity of
heat is set free, precisely the same amount of heat is absorbed, or
disappears, when the latter substance is decomposed to form the same
quantities of the original substances; and, _per contra_, if the
combination is attended by a disappearance of heat, exactly the same
amount is liberated when the compound is broken up into its first
constituents. Compounds are therefore of two kinds: those which absorb
heat during their preparation, and consequently liberate heat when they
are decomposed--such being termed endothermic; and those which evolve
heat during their preparation, and consequently absorb heat when they are
decomposed--such being called exothermic. If a substance absorbs heat
during its formation, it cannot be produced unless that heat is supplied
to it; and since heat, being a form of motion, is equally a form of
energy, energy must be supplied, or work must be done, before that
substance can be obtained. Conversely, if a substance evolves heat during
its formation, its component parts evolve energy when the said substance
is being produced; and therefore the mere act of combination is
accompanied by a facility for doing work, which work may be applied in
assisting some other reaction that requires heat, or may be usefully
employed in any other fashion, or wasted if necessary. Seeing that there
is a tendency in nature for the steady dissipation of energy, it follows
that an exothermic substance is stable, for it tends to remain as it is
unless heat is supplied to it, or work is done upon it; whereas,
according to its degree of endothermicity, an endothermic substance is
more or less unstable, for it is always ready to emit heat, or to do
work, as soon as an opportunity is given to it to decompose. The
theoretical and practical results of this circumstance will be elaborated
in Chapter VI., when the endothermic nature of acetylene is more fully

A very simple experiment will show that a notable quantity of heat is set
free when calcium carbide is brought into contact with water, and by
arranging the details of the apparatus in a suitable manner, the quantity
of heat manifested may be measured with considerable accuracy. A lengthy
description of the method of performing this operation, however, scarcely
comes within the province of the present book, and it must be sufficient
to say that the heat is estimated by decomposing a known weight of
carbide by means of water in a small vessel surrounded on all sides by a
carefully jacketed receptacle full of water and provided with a sensitive
thermometer. The quantity of water contained in the outer vessel being
known, and its temperature having been noted before the reaction
commences, an observation of the thermometer after the decomposition is
finished, and when the mercury has reached its highest point, gives data
which show that the reaction between water and a known weight of calcium
carbide produces heat sufficient in amount to raise a known weight of
water through a known thermometric distance; and from these figures the
corresponding number of large calories may easily be calculated. A
determination of this quantity of heat has been made experimentally by
several investigators, including Lewes, who has found that the heat
evolved on decomposing 1 gramme of ordinary commercial carbide with water
is 0.406 large calorie. [Footnote: Lewes returns his result as 406
calories, because he employs the "small calorie." The small calorie is
the quantity of heat needed to raise 1 gramme of water 1 deg. C.; but as
there are 1000 grammes in 1 kilogramme, the large calorie is equal to
1000 small calories. In many respects the former unit is to be
preferred.] As the material operated upon contained only 91.3 per cent.
of true calcium carbide, he estimates the heat corresponding with the
decomposition of 1 gramme of pure carbide to be 0.4446 large calorie. As,
however, it is better, and more in accordance with modern practice, to
quote such data in terms of the atomic or molecular weight of the
substance concerned, and as the molecular weight of calcium carbide is
64, it is preferable to multiply these figures by 64, stating that,
according to Lewes' researches, the heat of decomposition of "1 gramme-
molecule" (_i.e._, 64 grammes) of a calcium carbide having a purity
of 91.3 per cent. is just under 26 calories, or that of 1 gramme-molecule
of pure carbide 28.454 calories. It is customary now to omit the phrase
"one gramme-molecule" in giving similar figures, physicists saying simply
that the heat of decomposition of calcium carbide by water when calcium
hydroxide is the by-product, is 28.454 large calories.

Assuming all the necessary data known, as happens to be the case in the
present instance, it is also possible to calculate theoretically the heat
which should be evolved on decomposing calcium carbide by means of water.
Equation (2), given on page 24, shows that of the substances taking part
in the reaction 1 molecular weight of calcium carbide is decomposed, and
1 molecular weight of acetylene is formed. Of the two molecules of water,
only one is decomposed, the other passing to the calcium hydroxide
unchanged; and the 1 molecule of calcium hydroxide is formed by the
combination of 1 atom of free calcium, 1 atom of free oxygen, and 1
molecule of water already existing as such. Calcium hydroxide and water
are both exothermic substances, absorbing heat when they are decomposed,
liberating it when they are formed. Acetylene is endothermic, liberating
heat when it is decomposed, absorbing it when it is produced.
Unfortunately there is still some doubt about the heat of formation of
calcium carbide, De Forcrand returning it as -0.65 calorie, and Gin as
+3.9 calories. De Forcrand's figure means, as before explained, that 64
grammes of carbide should absorb 0.65 large calorie when they are
produced by the combination of 40 grammes of calcium with 24 grammes of
carbon; the minus sign calling attention to the belief that calcium
carbide is endothermic, heat being liberated when it suffers
decomposition. On the contrary, Gin's figure expresses the idea that
calcium carbide is exothermic, liberating 3.9 calories when it is
produced, and absorbing them when it is decomposed. In the absence of
corroborative evidence one way or the other, Gin's determination will be
accepted for the ensuing calculation. In equation (2), therefore, calcium
carbide is decomposed and absorbs heat; water is decomposed and absorbs
heat; acetylene is produced and absorbs heat; and calcium hydroxide is
produced liberating heat. On consulting the tables of thermo-chemical
data given in the various text-books on physical chemistry, all the other
constants needed for the present purpose will be found; and it will
appear that the heat of formation of water is +69 calories, that of
acetylene -58.1 calories, and that of calcium hydroxide, when 1 atom of
calcium, 1 atom of oxygen, and 1 molecule of water unite together, is
+160.1 calories. [Footnote: When 1 atom of calcium, 2 atoms of oxygen,
and 2 atoms of hydrogen unite to form solid calcium hydroxide, the heat
of formation of the latter is 229.1 (cf. _infra_). This value is
simply 160.1 + 69.0 = 229.1; 69.0 being the heat of formation of water.]
Collecting the results into the form of a balance-sheet, the effect of
decomposing calcium carbide with water is this:

_Heat liberated._ | _Heat absorbed._
Formation of Ca(OH)_2 16O.1 | Formation of acetylene 58.1
| Decomposition of water 69.0
| Decomposition of carbide 3.9
| Balance 29.1
_____ | _____
Total 160.1 | Total 160.1

Therefore when 64 grammes of calcium carbide are decomposed by water, or
when 18 grammes of water are decomposed by calcium carbide (the by-
product in each case being calcium hydroxide or slaked lime, for the
formation of which a further 18 grammes of water must be present in the
second instance), 29.1 large calories are set free. It is not possible
yet to determine thermo-chemical data with extreme accuracy, especially
on such a material as calcium carbide, which is hardly to be procured in
a state of chemical purity; and so the value 28.454 calories
experimentally found by Lewes agrees very satisfactorily, considering all
things, with the calculated value 29.1 calories. It is to be noticed,
however, that the above calculated value has been deduced on the
assumption that the calcium hydroxide is obtained as a dry powder; but as
slaked lime is somewhat soluble in water, and as it evolves 3 calories in
so dissolving, if sufficient water is present to take up the calcium
hydroxide entirely into the liquid form (_i.e._, that of a
solution), the amount of heat set free will be greater by those 3
calories, _i.e._, 32.1 large calories altogether.

THE PROCESS OF GENERATION.--Taking 28 as the number of large calories
developed when 64 grammes of ordinary commercial calcium carbide are
decomposed with sufficient water to leave dry solid calcium hydroxide as
the by-product in acetylene generation, this quantity of heat is capable
of exerting any of the following effects. It is sufficient (1) to raise
1000 grammes of water through 28 deg. C., say from 10 deg. C. (50 deg. F.,
which is roughly the temperature of ordinary cold water) to 38 deg. C. It
is sufficient (2) to raise 64 grammes of water (a weight equal to that of
the carbide decomposed) through 438 deg. C., if that were possible. It would
raise (3) 311 grammes of water through 90 deg. C., _i.e._, from 10 deg. C.
to the boiling-point. If, however, instead of remaining in the liquid state,
the water were converted into vapour, the same quantity of heat would
suffice (4) to change 44.7 grammes of water at 10 deg. C. into steam at
100 deg. C.; or (5) to change 46.7 grammes of water at 10 deg. C. into
vapour at the same temperature. It is an action of the last character which
takes place in acetylene generators of the most modern and usual pattern,
some of the surplus water being evaporated and carried away as vapour at a
comparatively low temperature with the escaping gas; for it must be
remembered that although steam, as such, condenses into liquid water
immediately the surrounding temperature falls below 100 deg. C., the vapour
of water remains uncondensed, even at temperatures below the freezing-
point, when that vapour is distributed among some permanent gas--the
precise quantity of vapour so remaining being a function of the
temperature and barometric height. Thus it appears that if the heat
evolved during the decomposition of calcium carbide is not otherwise
consumed, it is sufficient in amount to vaporise almost exactly 3 parts
by weight of water for every 4 parts of carbide attacked; but if it were
expended upon some substance such as acetylene, calcium carbide, or
steel, which, unlike water, could not absorb an extra amount by changing
its physical state (from solid to liquid, or from liquid to gas), the
heat generated during the decomposition of a given weight of carbide
would suffice to raise an equal weight of the particular substance under
consideration to a temperature vastly exceeding 438 deg. C. The temperature
attained, indeed, measured in Centigrade degrees, would be 438 multiplied
by the quotient obtained on dividing the specific heat of water by the
specific heat of the substance considered: which quotient, obviously, is
the "reciprocal" of the specific heat of the said substance.

The analogy to the combustion of coal mentioned on a previous page shows
that although the quantity of heat evolved during a certain chemical
reaction is strictly fixed, the temperature attained is dependent on the
time over which the reaction is spread, being higher as the process is
more rapid. This is due to the fact that throughout the whole period of
reaction heat is escaping from the mass, and passing into the atmosphere
at a fairly constant speed; so that, clearly, the more slowly heat is
produced, the better opportunity has it to pass away, and the less of it
is left to collect in the material under consideration. During the action
of an acetylene generator, there is a current of gas constantly
travelling away from the carbide, there is vapour of water constantly
escaping with the gas, there are the walls of the generator itself
constantly exposed to the cooling action of the atmosphere, and there is
either a mass of calcium carbide or of water within the generator. It is
essential for good working that the temperature of both the acetylene and
the carbide shall be prevented from rising to any noteworthy extent;
while the amount of heat capable of being dissipated into the air through
the walls of the apparatus in a given time is narrowly limited, depending
upon the size and shape of the generator, and the temperature of the
surrounding air. If, then, a small, suitably designed generator is
working quite slowly, the loss of heat through the external walls of the
apparatus may easily be rapid enough to prevent the internal temperature
from rising objectionably high; but the larger the generator, and the
more rapidly it is evolving gas, the less does this become possible.
Since of the substances in or about a generator water is the one which
has by far the largest capacity for absorbing heat, and since it is the
only substance to which any necessary quantity of heat can be safely or
conveniently transmitted, it follows that the larger in size an acetylene
generator is, or the more rapidly that generator is made to deliver gas,
the more desirable is it to use water as the means for dissipating the
surplus heat, and the more necessary is it to employ an apparatus in
which water is in large chemical excess at the actual place of

The argument is sometimes advanced that an acetylene generator containing
carbide in excess will work satisfactorily without exhibiting an
undesirable rise in internal temperature, if the vessel holding the
carbide is merely surrounded by a large quantity of cold water. The idea
is that the heat evolved in that particular portion of the charge which
is suffering decomposition will be communicated with sufficient speed
throughout the whole mass of calcium carbide present, whence it will pass
through the walls of the containing vessel into the water all round.
Provided the generator is quite small, provided the carbide container is
so constructed as to possess the maximum of superficial area with the
minimum of cubical capacity (a geometrical form to which the sphere, and
in one direction the cylinder, are diametrically opposed), and provided
the walls of the container do not become coated internally or externally
with a coating of lime or water scale so as to diminish in heat-
transmitting power, an apparatus designed in the manner indicated is
undoubtedly free from grave objection; but immediately any of those
provisions is neglected, trouble is likely to ensue, for the heat will
not disappear from the place of actual reaction at the necessary speed.
Apparent proof that heat is not accumulating unduly in a water-jacketed
carbide container even when the generator is evolving gas at a fair speed
is easy to obtain; for if, as usually happens, the end of the container
through which the carbide is inserted is exposed to the air, the hand may
be placed upon it, and it will be found to be only slightly warm to the
touch. Such a test, however, is inconclusive, and frequently misleading,
because if more than a pound or two of carbide is present as an undivided
mass, and if water is allowed to attack one portion of it, that
particular portion may attain a high temperature while the rest is
comparatively cool: and if the bulk of the carbide is comparatively cool,
naturally the walls of the containing vessel themselves remain
practically unheated. Three causes work together to prevent this heat
being dissipated through the walls of the carbide vessel with sufficient
rapidity. In the first place, calcium carbide itself is a very bad
conductor of heat. So deficient in heat-conducting power is it that a
lump a few inches in diameter may be raised to redness in a gas flame at
one spot, and kept hot for some minutes, while the rest of the mass
remains sufficiently cool to be held comfortably in the fingers. In the
second place, commercial carbide exists in masses of highly irregular
shape, so that when they are packed into any vessel they only touch at
their angles and edges; and accordingly, even if the material were a
fairly good heat conductor of itself, the air or gas present between each
lump would act as an insulator, protecting the second piece from the heat
generated in the first. In the third place, the calcium hydroxide
produced as the by-product when calcium carbide is decomposed by water
occupies considerably more space than the original carbide--usually two
or three times as much space, the exact figures depending upon the
conditions in which it is formed--and therefore a carbide container
cannot advisedly be charged with more than one-third the quantity of
solid which it is apparently capable of holding. The remaining two-thirds
of the space is naturally full of air when the container is first put
into the generator, but the air is displaced by acetylene as soon as gas
production begins. Whether that space, however, is occupied by air, by
acetylene, or by a gradually growing loose mass of slaked lime, each
separate lump of hot carbide is isolated from its neighbours by a
material which is also a very bad heat conductor; and the heat has but
little opportunity of distributing itself evenly. Moreover, although iron
or steel is a notably better conductor of heat than any of the other
substances present in the carbide vessel, it is, as a metal, only a poor
conductor, being considerably inferior in this respect to copper. If heat
dissipation were the only point to be studied in the construction of an
acetylene apparatus, far better results might be obtained by the
employment of copper for the walls of the carbide container; and possibly
in that case a generator of considerable size, fitted with a water-

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