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Familiar Letters on Chemistry by Justus Liebig

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Second Edition, Corrected.




The Letters contained in this little Volume embrace some of the most
important points of the science of Chemistry, in their application
to Natural Philosophy, Physiology, Agriculture, and Commerce. Some
of them treat of subjects which have already been, or will hereafter
be, more fully discussed in my larger works. They were intended to
be mere sketches, and were written for the especial purpose of
exciting the attention of governments, and an enlightened public, to
the necessity of establishing Schools of Chemistry, and of
promoting, by every means, the study of a science so intimately
connected with the arts, pursuits, and social well-being of modern
civilised nations.

For my own part I do not scruple to avow the conviction, that ere
long, a knowledge of the principal truths of Chemistry will be
expected in every educated man, and that it will be as necessary to
the Statesman, the Political Economist, and the Practical
Agriculturist, as it is already indispensable to the Physician, and
the Manufacturer.

In Germany, such of these Letters as have been already published,
have not failed to produce some of the results anticipated. New
professorships have been established in the Universities of
Goettingen and Wuertzburg, for the express purpose of facilitating
the application of chemical truths to the practical arts of life,
and of following up the new line of investigation and research--the
bearing of Chemistry upon Physiology, Medicine, and
Agriculture,--which may be said to be only just begun.

My friend, Dr. Ernest Dieffenbach, one of my first pupils, who is
well acquainted with all the branches of Chemistry, Physics, Natural
History, and Medicine, suggested to me that a collection of these
Letters would be acceptable to the English public, which has so
favourably received my former works.

I readily acquiesced in the publication of an English edition, and
undertook to write a few additional Letters, which should embrace
some conclusions I have arrived at, in my recent investigations, in
connection with the application of chemical science to the
physiology of plants and agriculture.

My esteemed friend, Dr. Gardner, has had the kindness to revise the
manuscript and the proof sheets for publication, for which I cannot
refrain expressing my best thanks.

It only remains for me to add a hope, that this little offering may
serve to make new friends to our beautiful and useful science, and
be a remembrancer to those old friends who have, for many years
past, taken a lively interest in all my labours.


Giessen, Aug. 1843.



The Subject proposed. Materials employed for Chemical Apparatus:--
the Ancients, represent the forms of matter. Lavoisier and his
successors. Study of the materials composing the Earth. Synthetic
production of Minerals--LAPIS LAZULI. Organic Chemistry.


Changes of Form which every kind of Matter undergoes. Conversion of
Gases into Liquids and Solids. Carbonic Acid--its curious properties
in a solid state. Condensation of Gases by porous bodies. By Spongy
Platinum. Importance of this property in Nature.


The Manufacture of Soda from Culinary Salt; its importance in the
Arts and in Commerce. Glass--Soap--Sulphuric Acid. Silver Refining.


Connection of Theory with Practice. Employment of MAGNETISM as a
moving power--its impracticability. Relation of Coals and Zinc as
economic sources of Force. Manufacture of Beet-root Sugar--its
impolicy. Gas for illumination.


ISOMERISM, or identity of composition in bodies with different
chemical and physical properties. CRYSTALLISATION. AMORPHISM.
ISOMORPHISM, or similarity of properties in bodies totally different
in composition.


nourishment, and materials for combustion. Effects of Atmospheric
Oxygen. Balance of CARBON and OXYGEN.


ANIMAL HEAT, its laws and influence on the Animal Functions. Loss
and SUPPLY. Influence of Climate. Fuel of Animal Heat. Agency of
Oxygen in Disease. Respiration.


ALIMENTS. Constituents of the Blood. Fibrine, Albumen. Inorganic
Substances. Isomerism of Fibrine, Albumen, and elements of
nutrition. Relation of animal and vegetable organisms.


Growth of Animals. Uses of Butter and Milk. Metamorphoses of
Tissues. Food of Carnivora, and of the Horse.


Application of the preceding facts to Man. Division of human Food.
Uses of Gelatine.


Causes of the exhaustion of Land. Virginia. England. Relief gained
by importation of bones. Empirical farming unsatisfactory. Necessity
for scientific principles. Influence of the atmosphere. Of Saline
and Earthy matters of the soil.


agricultural processes. Washing for gold.


AGRICULTURE. Manner in which FALLOW ameliorates the soil. Uses of
Lime. Effects of Burning. Of Marl.


NATURE AND EFFECTS OF MANURES. Animal bodies subject to constant
waste. Parts separating--exuviae--waste vegetable matters--together
contain all the elements of the soil and of food. Various value of
excrements of different animals as manure.


Forests and Meadows supplied only with mineral aliments prove it to
be from the atmosphere. Relations between Mineral constituents, and
Carbon and Nitrogen. Effects of the Carbonic Acid and Ammonia of
Manures. Necessity of inorganic constituents to the formation of
aliments, of blood, and therefore of nutrition. NECESSITY OF


the PHOSPHATES OF LIME and ALKALIES to the cultivation of the
CEREALIA. Sources of a SUPPLY of these MATERIALS.



My dear Sir,

The influence which the science of chemistry exercises upon human
industry, agriculture, and commerce; upon physiology, medicine, and
other sciences, is now so interesting a topic of conversation
everywhere, that it may be no unacceptable present to you if I trace
in a few familiar letters some of the relations it bears to these
various sciences, and exhibit for you its actual effect upon the
present social condition of mankind.

In speaking of the present state of chemistry, its rise and
progress, I shall need no apology if, as a preliminary step, I call
your attention to the implements which the chemist employs--the
means which are indispensable to his labours and to his success.

These consist, generally, of materials furnished to us by nature,
endowed with many most remarkable properties fitting them for our
purposes; if one of them is a production of art, yet its adaptation
to the use of mankind,--the qualities which render it available to
us,--must be referred to the same source as those derived
immediately from nature.

Cork, Platinum, Glass, and Caoutchouc, are the substances to which I
allude, and which minister so essentially to modern chemical
investigations. Without them, indeed, we might have made some
progress, but it would have been slow; we might have accomplished
much, but it would have been far less than has been done with their
aid. Some persons, by the employment of expensive substances, might
have successfully pursued the science; but incalculably fewer minds
would have been engaged in its advancement. These materials have
only been duly appreciated and fully adopted within a very recent
period. In the time of Lavoisier, the rich alone could make chemical
researches; the necessary apparatus could only be procured at a very
great expense.

And first, of Glass: every one is familiar with most of the
properties of this curious substance; its transparency, hardness,
destitution of colour, and stability under ordinary circumstances:
to these obvious qualities we may add those which especially adapt
it to the use of the chemist, namely, that it is unaffected by most
acids or other fluids contained within it. At certain temperatures
it becomes more ductile and plastic than wax, and may be made to
assume in our hands, before the flame of a common lamp, the form of
every vessel we need to contain our materials, and of every
apparatus required to pursue our experiments.

Then, how admirable and valuable are the properties of Cork! How
little do men reflect upon the inestimable worth of so common a
substance! How few rightly esteem the importance of it to the
progress of science, and the moral advancement of mankind!--There is
no production of nature or art equally adapted to the purposes to
which the chemist applies it. Cork consists of a soft, highly
elastic substance, as a basis, having diffused throughout a matter
with properties resembling wax, tallow, and resin, yet dissimilar to
all of these, and termed suberin. This renders it perfectly
impermeable to fluids, and, in a great measure, even to gases. It is
thus the fittest material we possess for closing our bottles, and
retaining their contents. By its means, and with the aid of
Caoutchouc, we connect our vessels and tubes of glass, and construct
the most complicated apparatus. We form joints and links of
connexion, adapt large apertures to small, and thus dispense
altogether with the aid of the brassfounder and the mechanist. Thus
the implements of the chemist are cheaply and easily procured,
immediately adapted to any purpose, and readily repaired or altered.

Again, in investigating the composition of solid bodies,--of
minerals,--we are under the necessity of bringing them into a liquid
state, either by solution or fusion. Now vessels of glass, of
porcelain, and of all non-metallic substances, are destroyed by the
means we employ for that purpose,--are acted upon by many acids, by
alkalies and the alkaline carbonates. Crucibles of gold and silver
would melt at high temperatures. But we have a combination of all
the qualities we can desire in Platinum. This metal was only first
adapted to these uses about fifty years since. It is cheaper than
gold, harder and more durable than silver, infusible at all
temperatures of our furnaces, and is left intact by acids and
alkaline carbonates. Platinum unites all the valuable properties of
gold and of porcelain, resisting the action of heat, and of almost
all chemical agents.

As no mineral analysis could be made perfectly without platinum
vessels, had we not possessed this metal, the composition of
minerals would have yet remained unknown; without cork and
caoutchouc we should have required the costly aid of the mechanician
at every step. Even without the latter of these adjuncts our
instruments would have been far more costly and fragile. Possessing
all these gifts of nature, we economise incalculably our time--to us
more precious than money!

Such are our instruments. An equal improvement has been accomplished
in our laboratory. This is no longer the damp, cold, fireproof vault
of the metallurgist, nor the manufactory of the druggist, fitted up
with stills and retorts. On the contrary, a light, warm, comfortable
room, where beautifully constructed lamps supply the place of
furnaces, and the pure and odourless flame of gas, or of spirits of
wine, supersedes coal and other fuel, and gives us all the fire we
need; where health is not invaded, nor the free exercise of thought
impeded: there we pursue our inquiries, and interrogate Nature to
reveal her secrets.

To these simple means must be added "The Balance," and then we
possess everything which is required for the most extensive

The great distinction between the manner of proceeding in chemistry
and natural philosophy is, that one weighs, the other measures. The
natural philosopher has applied his measures to nature for many
centuries, but only for fifty years have we attempted to advance our
philosophy by weighing.

For all great discoveries chemists are indebted to the
"balance"--that incomparable instrument which gives permanence to
every observation, dispels all ambiguity, establishes truth, detects
error, and guides us in the true path of inductive science.

The balance, once adopted as a means of investigating nature, put an
end to the school of Aristotle in physics. The explanation of
natural phenomena by mere fanciful speculations, gave place to a
true natural philosophy. Fire, air, earth, and water, could no
longer be regarded as elements. Three of them could henceforth be
considered only as significative of the forms in which all matter
exists. Everything with which we are conversant upon the surface of
the earth is solid, liquid, or aeriform; but the notion of the
elementary nature of air, earth, and water, so universally held, was
now discovered to belong to the errors of the past.

Fire was found to be but the visible and otherwise perceptible
indication of changes proceeding within the, so called, elements.

Lavoisier investigated the composition of the atmosphere and of
water, and studied the many wonderful offices performed by an
element common to both in the scheme of nature, namely, oxygen: and
he discovered many of the properties of this elementary gas.

After his time, the principal problem of chemical philosophers was
to determine the composition of the solid matters composing the
earth. To the eighteen metals previously known were soon added
twenty-four discovered to be constituents of minerals. The great
mass of the earth was shown to be composed of metals in combination
with oxygen, to which they are united in one, two, or more definite
and unalterable proportions, forming compounds which are termed
metallic oxides, and these, again, combined with oxides of other
bodies, essentially different to metals, namely, carbon and
silicium. If to these we add certain compounds of sulphur with
metals, in which the sulphur takes the place of oxygen, and forms
sulphurets, and one other body,--common salt,--(which is a compound
of sodium and chlorine), we have every substance which exists in a
solid form upon our globe in any very considerable mass. Other
compounds, innumerably various, are found only in small scattered

The chemist, however, did not remain satisfied with the separation
of minerals into their component elements, i.e. their analysis; but
he sought by synthesis, i.e. by combining the separate elements and
forming substances similar to those constructed by nature, to prove
the accuracy of his processes and the correctness of his
conclusions. Thus he formed, for instance, pumice-stone, feldspar,
mica, iron pyrites, &c. artificially.

But of all the achievements of inorganic chemistry, the artificial
formation of lapis lazuli was the most brilliant and the most
conclusive. This mineral, as presented to us by nature, is
calculated powerfully to arrest our attention by its beautiful
azure-blue colour, its remaining unchanged by exposure to air or to
fire, and furnishing us with a most valuable pigment, Ultramarine,
more precious than gold!

The analysis of lapis lazuli represented it to be composed of
silica, alumina, and soda, three colourless bodies, with sulphur and
a trace of iron. Nothing could be discovered in it of the nature of
a pigment, nothing to which its blue colour could be referred, the
cause of which was searched for in vain. It might therefore have
been supposed that the analyst was here altogether at fault, and
that at any rate its artificial production must be impossible.
Nevertheless, this has been accomplished, and simply by combining in
the proper proportions, as determined by analysis, silica, alumina,
soda, iron, and sulphur. Thousands of pounds weight are now
manufactured from these ingredients, and this artificial ultramarine
is as beautiful as the natural, while for the price of a single
ounce of the latter we may obtain many pounds of the former.

With the production of artificial lapis lazuli, the formation of
mineral bodies by synthesis ceased to be a scientific problem to the
chemist; he has no longer sufficient interest in it to pursue the
subject. He may now be satisfied that analysis will reveal to him
the true constitution of minerals. But to the mineralogist and
geologist it is still in a great measure an unexplored field,
offering inquiries of the highest interest and importance to their

After becoming acquainted with the constituent elements of all the
substances within our reach and the mutual relations of these
elements, the remarkable transmutations to which the bodies are
subject under the influence of the vital powers of plants and
animals, became the principal object of chemical investigations, and
the highest point of interest. A new science, inexhaustible as life
itself, is here presented us, standing upon the sound and solid
foundation of a well established inorganic chemistry. Thus the
progress of science is, like the development of nature's works,
gradual and expansive. After the buds and branches spring forth the
leaves and blossoms, after the blossoms the fruit.

Chemistry, in its application to animals and vegetables. endeavours
jointly with physiology to enlighten us respecting the mysterious
processes and sources of organic life.


My dear Sir,

In my former letter I reminded you that three of the supposed
elements of the ancients represent the forms or state in which all
the ponderable matter of our globe exists; I would now observe, that
no substance possesses absolutely any one of those conditions; that
modern chemistry recognises nothing unchangeably solid, liquid, or
aeriform: means have been devised for effecting a change of state in
almost every known substance. Platinum, alumina, and rock crystal,
it is true, cannot be liquified by the most intense heat of our
furnaces, but they melt like wax before the flame of the
oxy-hydrogen blowpipe. On the other hand, of the twenty-eight
gaseous bodies with which we are acquainted, twenty-five may be
reduced to a liquid state, and one into a solid. Probably, ere long,
similar changes of condition will be extended to every form of

There are many things relating to this condensation of the gases
worthy of your attention. Most aeriform bodies, when subjected to
compression, are made to occupy a space which diminishes in the
exact ratio of the increase of the compressing force. Very
generally, under a force double or triple of the ordinary
atmospheric pressure, they become one half or one third their former
volume. This was a long time considered to be a law, and known as
the law of Marriotte; but a more accurate study of the subject has
demonstrated that this law is by no means of general application.
The volume of certain gases does not decrease in the ratio of the
increase of the force used to compress them, but in some, a
diminution of their bulk takes place in a far greater degree as the
pressure increases.

Again, if ammoniacal gas is reduced by a compressing force to
one-sixth of its volume, or carbonic acid is reduced to one
thirty-sixth, a portion of them loses entirely the form of a gas,
and becomes a liquid, which, when the pressure is withdrawn, assumes
again in an instant its gaseous state--another deviation from the
law of Marriotte.

Our process for reducing gases into fluids is of admirable
simplicity. A simple bent tube, or a reduction of temperature by
artificial means, have superseded the powerful compressing machines
of the early experimenters.

The cyanuret of mercury, when heated in an open glass tube, is
resolved into cyanogen gas and metallic mercury; if this substance
is heated in a tube hermetically sealed, the decomposition occurs as
before, but the gas, unable to escape, and shut up in a space
several hundred times smaller than it would occupy as gas under the
ordinary atmospheric pressure, becomes a fluid in that part of the
tube which is kept cool.

When sulphuric acid is poured upon limestone in an open vessel,
carbonic acid escapes with effervescence as a gas, but if the
decomposition is effected in a strong, close, and suitable vessel of
iron, we obtain the carbonic acid in the state of liquid. In this
manner it may be obtained in considerable quantities, even many
pounds weight. Carbonic acid is separated from other bodies with
which it is combined as a fluid under a pressure of thirty-six

The curious properties of fluid carbonic acid are now generally
known. When a small quantity is permitted to escape into the
atmosphere, it assumes its gaseous state with extraordinary
rapidity, and deprives the remaining fluid of caloric so rapidly
that it congeals into a white crystalline mass like snow: at first,
indeed, it was thought to be really snow, but upon examination it
proved to be pure frozen carbonic acid. This solid, contrary to
expectation, exercises only a feeble pressure upon the surrounding
medium. The fluid acid inclosed in a glass tube rushes at once, when
opened, into a gaseous state, with an explosion which shatters the
tube into fragments; but solid carbonic acid can be handled without
producing any other effect than a feeling of intense cold. The
particles of the carbonic acid being so closely approximated in the
solid, the whole force of cohesive attraction (which in the fluid is
weak) becomes exerted, and opposes its tendency to assume its
gaseous state; but as it receives heat from surrounding bodies, it
passes into gas gradually and without violence. The transition of
solid carbonic acid into gas deprives all around it of caloric so
rapidly and to so great an extent, that a degree of cold is produced
immeasurably great, the greatest indeed known. Ten, twenty, or more
pounds weight of mercury, brought into contact with a mixture of
ether and solid carbonic acid, becomes in a few moments firm and
malleable. This, however, cannot be accomplished without
considerable danger. A melancholy accident occurred at Paris, which
will probably prevent for the future the formation of solid carbonic
acid in these large quantities, and deprive the next generation of
the gratification of witnessing these curious experiments. Just
before the commencement of the lecture in the Laboratory of the
Polytechnic School, an iron cylinder, two feet and a half long and
one foot in diameter, in which carbonic acid had been developed for
experiment before the class, burst, and its fragments were scattered
about with the most tremendous force; it cut off both the legs of
the assistant and killed him on the spot. This vessel, formed of the
strongest cast-iron, and shaped like a cannon, had often been
employed to exhibit experiments in the presence of the students. We
can scarcely think, without shuddering, of the dreadful calamity
such an explosion would have occasioned in a hall filled with

When we had ascertained the fact of gases becoming fluid under the
influence of cold or pressure, a curious property possessed by
charcoal, that of absorbing gas to the extent of many times its
volume,--ten, twenty, or even as in the case of ammoniacal gas or
muriatic acid gas, eighty or ninety fold,--which had been long
known, no longer remained a mystery. Some gases are absorbed and
condensed within the pores of the charcoal, into a space several
hundred times smaller than they before occupied; and there is now no
doubt they there become fluid, or assume a solid state. As in a
thousand other instances, chemical action here supplants mechanical
forces. Adhesion or heterogeneous attraction, as it is termed,
acquired by this discovery a more extended meaning; it had never
before been thought of as a cause of change of state in matter; but
it is now evident that a gas adheres to the surface of a solid body
by the same force which condenses it into a liquid.

The smallest amount of a gas,--atmospheric air for instance,--can be
compressed into a space a thousand times smaller by mere mechanical
pressure, and then its bulk must be to the least measurable surface
of a solid body, as a grain of sand to a mountain. By the mere
effect of mass,--the force of gravity,--gaseous molecules are
attracted by solids and adhere to their surfaces; and when to this
physical force is added the feeblest chemical affinity, the
liquifiable gases cannot retain their gaseous state. The amount of
air condensed by these forces upon a square inch of surface is
certainly not measurable; but when a solid body, presenting several
hundred square feet of surface within the space of a cubic inch, is
brought into a limited volume of gas, we may understand why that
volume is diminished, why all gases without exception are absorbed.
A cubic inch of charcoal must have, at the lowest computation, a
surface of one hundred square feet. This property of absorbing gases
varies with different kinds of charcoal: it is possessed in a higher
degree by those containing the most pores, i.e. where the pores are
finer; and in a lower degree in the more spongy kinds, i.e. where
the pores are larger.

In this manner every porous body--rocks, stones, the clods of the
fields, &c.,--imbibe air, and therefore oxygen; the smallest solid
molecule is thus surrounded by its own atmosphere of condensed
oxygen; and if in their vicinity other bodies exist which have an
affinity for oxygen, a combination is effected. When, for instance,
carbon and hydrogen are thus present, they are converted into
nourishment for vegetables,--into carbonic acid and water. The
development of heat when air is imbibed, and the production of steam
when the earth is moistened by rain, are acknowledged to be
consequences of this condensation by the action of surfaces.

But the most remarkable and interesting case of this kind of action
is the imbibition of oxygen by metallic platinum. This metal, when
massive, is of a lustrous white colour, but it may be brought, by
separating it from its solutions, into so finely divided a state,
that its particles no longer reflect light, and it forms a powder as
black as soot. In this condition it absorbs eight hundred times its
volume of oxygen gas, and this oxygen must be contained within it in
a state of condensation very like that of fluid water.

When gases are thus condensed, i.e. their particles made to
approximate in this extraordinary manner, their properties can be
palpably shown. Their chemical actions become apparent as their
physical characteristic disappears. The latter consists in the
continual tendency of their particles to separate from each other;
and it is easy to imagine that this elasticity of gaseous bodies is
the principal impediment to the operation of their chemical force;
for this becomes more energetic as their particles approximate. In
that state in which they exist within the pores or upon the surface
of solid bodies, their repulsion ceases, and their whole chemical
action is exerted. Thus combinations which oxygen cannot enter into,
decompositions which it cannot effect while in the state of gas,
take place with the greatest facility in the pores of platinum
containing condensed oxygen. When a jet of hydrogen gas, for
instance, is thrown upon spongy platinum, it combines with the
oxygen condensed in the interior of the mass; at their point of
contact water is formed, and as the immediate consequence heat is
evolved; the platinum becomes red hot and the gas is inflamed. If we
interrupt the current of the gas, the pores of the platinum become
instantaneously filled again with oxygen; and the same phenomenon
can be repeated a second time, and so on interminably.

In finely pulverised platinum, and even in spongy platinum, we
therefore possess a perpetuum mobile--a mechanism like a watch which
runs out and winds itself up--a force which is never
exhausted--competent to produce effects of the most powerful kind,
and self-renewed ad infinitum.

Many phenomena, formerly inexplicable, are satisfactorily explained
by these recently discovered properties of porous bodies. The
metamorphosis of alcohol into acetic acid, by the process known as
the quick vinegar manufacture, depends upon principles, at a
knowledge of which we have arrived by a careful study of these


My dear Sir,

The manufacture of soda from common culinary salt, may be regarded
as the foundation of all our modern improvements in the domestic
arts; and we may take it as affording an excellent illustration of
the dependence of the various branches of human industry and
commerce upon each other, and their relation to chemistry.

Soda has been used from time immemorial in the manufacture of soap
and glass, two chemical productions which employ and keep in
circulation an immense amount of capital. The quantity of soap
consumed by a nation would be no inaccurate measure whereby to
estimate its wealth and civilisation. Of two countries, with an
equal amount of population, the wealthiest and most highly civilised
will consume the greatest weight of soap. This consumption does not
subserve sensual gratification, nor depend upon fashion, but upon
the feeling of the beauty, comfort, and welfare, attendant upon
cleanliness; and a regard to this feeling is coincident with wealth
and civilisation. The rich in the middle ages concealed a want of
cleanliness in their clothes and persons under a profusion of costly
scents and essences, whilst they were more luxurious in eating and
drinking, in apparel and horses. With us a want of cleanliness is
equivalent to insupportable misery and misfortune.

Soap belongs to those manufactured products, the money value of
which continually disappears from circulation, and requires to be
continually renewed. It is one of the few substances which are
entirely consumed by use, leaving no product of any worth. Broken
glass and bottles are by no means absolutely worthless; for rags we
may purchase new cloth, but soap-water has no value whatever. It
would be interesting to know accurately the amount of capital
involved in the manufacture of soap; it is certainly as large as
that employed in the coffee trade, with this important difference as
respects Germany, that it is entirely derived from our own soil.

France formerly imported soda from Spain,--Spanish sodas being of
the best quality--at an annual expenditure of twenty to thirty
millions of francs. During the war with England the price of soda,
and consequently of soap and glass, rose continually; and all
manufactures suffered in consequence.

The present method of making soda from common salt was discovered by
Le Blanc at the end of the last century. It was a rich boon for
France, and became of the highest importance during the wars of
Napoleon. In a very short time it was manufactured to an
extraordinary extent, especially at the seat of the soap
manufactories. Marseilles possessed for a time a monopoly of soda
and soap. The policy of Napoleon deprived that city of the
advantages derived from this great source of commerce, and thus
excited the hostility of the population to his dynasty, which became
favourable to the restoration of the Bourbons. A curious result of
an improvement in a chemical manufacture! It was not long, however,
in reaching England.

In order to prepare the soda of commerce (which is the carbonate)
from common salt, it is first converted into Glauber's salt
(sulphate of soda). For this purpose 80 pounds weight of
concentrated sulphuric acid (oil of vitriol) are required to 100
pounds of common salt. The duty upon salt checked, for a short time,
the full advantage of this discovery; but when the Government
repealed the duty, and its price was reduced to its minimum, the
cost of soda depended upon that of sulphuric acid.

The demand for sulphuric acid now increased to an immense extent;
and, to supply it, capital was embarked abundantly, as it afforded
an excellent remuneration. the origin and formation of sulphuric
acid was studied most carefully; and from year to year, better,
simpler, and cheaper methods of making it were discovered. With
every improvement in the mode of manufacture, its price fell; and
its sale increased in an equal ratio.

Sulphuric acid is now manufactured in leaden chambers, of such
magnitude that they would contain the whole of an ordinary-sized
house. As regards the process and the apparatus, this manufacture
has reached its acme--scarcely is either susceptible of improvement.
The leaden plates of which the chambers are constructed, requiring
to be joined together with lead (since tin or solder would be acted
on by the acid), this process was, until lately, as expensive as the
plates themselves; but now, by means of the oxy-hydrogen blowpipe,
the plates are cemented together at their edges by mere fusion,
without the intervention of any kind of solder.

And then, as to the process: according to theory, 100 pounds weight
of sulphur ought to produce 306 pounds of sulphuric acid; in
practice 300 pounds are actually obtained; the amount of loss is
therefore too insignificant for consideration.

Again; saltpetre being indispensable in making sulphuric acid, the
commercial value of that salt had formerly an important influence
upon its price. It is true that 100 pounds of saltpetre only are
required to 1000 pounds of sulphur; but its cost was four times
greater than an equal weight of the latter.

Travellers had observed near the small seaport of Yquiqui, in the
district of Atacama, in Peru, an efflorescence covering the ground
over extensive districts. This was found to consist principally of
nitrate of soda. Advantage was quickly taken of this discovery. The
quantity of this valuable salt proved to be inexhaustible, as it
exists in beds extending over more than 200 square miles. It was
brought to England at less than half the freight of the East India
saltpetre (nitrate of potassa); and as, in the chemical manufacture
neither the potash nor the soda were required, but only the nitric
acid, in combination with the alkali, the soda-saltpetre of South
America soon supplanted the potash-nitre of the East. The
manufacture of sulphuric acid received a new impulse; its price was
much diminished without injury to the manufacturer; and, with the
exception of fluctuations caused by the impediments thrown in the
way of the export of sulphur from Sicily, it soon became reduced to
a minimum, and remained stationary.

Potash-saltpetre is now only employed in the manufacture of
gunpowder; it is no longer in demand for other purposes; and thus,
if Government effect a saving of many hundred thousand pounds
annually in gunpowder, this economy must be attributed to the
increased manufacture of sulphuric acid.

We may form an idea of the amount of sulphuric acid consumed, when
we find that 50,000 pounds weight are made by a small manufactory,
and from 200,000 to 600,000 pounds by a large one annually. This
manufacture causes immense sums to flow annually into Sicily. It has
introduced industry and wealth into the arid and desolate districts
of Atacama. It has enabled us to obtain platina from its ores at a
moderate and yet remunerating price; since the vats employed for
concentrating this acid are constructed of this metal, and cost from
1000l. to 2000l. sterling. It leads to frequent improvements in the
manufacture of glass, which continually becomes cheaper and more
beautiful. It enables us to return to our fields all their potash--a
most valuable and important manure--in the form of ashes, by
substituting soda in the manufacture of glass and soap.

It is impossible to trace, within the compass of a letter, all the
ramifications of this tissue of changes and improvements resulting
from one chemical manufacture; but I must still claim your attention
to a few more of its most important and immediate results. I have
already told you, that in the manufacture of soda from culinary
salt, it is first converted into sulphate of soda. In this first
part of the process, the action of sulphuric acid produces muriatic
acid to the extent of one-and-a-half the amount of the sulphuric
acid employed. At first, the profit upon the soda was so great, that
no one took the trouble to collect the muriatic acid: indeed it had
no commercial value. A profitable application of it was, however,
soon discovered: it is a compound of chlorine, and this substance
may be obtained from it purer than from any other source. The
bleaching power of chlorine has long been known; but it was only
employed upon a large scale after it was obtained from this
residuary muriatic acid, and it was found that in combination with
lime it could be transported to distances without inconvenience.
Thenceforth it was used for bleaching cotton; and, but for this new
bleaching process, it would scarcely have been possible for the
cotton manufacture of Great Britain to have attained its present
enormous extent,--it could not have competed in price with France
and Germany. In the old process of bleaching, every piece must be
exposed to the air and light during several weeks in the summer, and
kept continually moist by manual labour. For this purpose, meadow
land, eligibly situated, was essential. Now a single establishment
near Glasgow bleaches 1400 pieces of cotton daily, throughout the
year. What an enormous capital would be required to purchase land
for this purpose! How greatly would it increase the cost of
bleaching to pay interest upon this capital, or to hire so much land
in England! This expense would scarcely have been felt in Germany.
Besides the diminished expense, the cotton stuffs bleached with
chlorine suffer less in the hands of skilful workmen than those
bleached in the sun; and already the peasantry in some parts of
Germany have adopted it, and find it advantageous.

Another use to which cheap muriatic acid is applied, is the
manufacture of glue from bones. Bone contains from 30 to 36 per
cent. of earthy matter--chiefly phosphate of lime, and the remainder
is gelatine. When bones are digested in muriatic acid they become
transparent and flexible like leather, the earthy matter is
dissolved, and after the acid is all carefully washed away, pieces
of glue of the same shape as the bones remain, which are soluble in
hot water and adapted to all the purposes of ordinary glue, without
further preparation.

Another important application of sulphuric acid may be adduced;
namely, to the refining of silver and the separation of gold, which
is always present in some proportion in native silver. Silver, as it
is usually obtained from mines in Europe, contains in 16 ounces, 6
to 8 ounces of copper. When used by the silversmith, or in coining,
16 ounces must contain in Germany 13 ounces of silver, in England
about 14 1/2. But this alloy is always made artificially by mixing
pure silver with the due proportion of the copper; and for this
purpose the silver must be obtained pure by the refiner. This he
formerly effected by amalgamation, or by roasting it with lead; and
the cost of this process was about 2l. for every hundred-weight of
silver. In the silver so prepared, about 1/1200 to 1/2000th part of
gold remained; to effect the separation of this by
nitrio-hydrochloric acid was more expensive than the value of the
gold; it was therefore left in utensils, or circulated in coin,
valueless. The copper, too, of the native silver was no use
whatever. But the 1/1000th part of gold, being about one and a half
per cent. of the value of the silver, now covers the cost of
refining, and affords an adequate profit to the refiner; so that he
effects the separation of the copper, and returns to his employer
the whole amount of the pure silver, as well as the copper, without
demanding any payment: he is amply remunerated by that minute
portion of gold. The new process of refining is a most beautiful
chemical operation: the granulated metal is boiled in concentrated
sulphuric acid, which dissolves both the silver and the copper,
leaving the gold nearly pure, in the form of a black powder. The
solution is then placed in a leaden vessel containing metallic
copper; this is gradually dissolved, and the silver precipitated in
a pure metallic state. The sulphate of copper thus formed is also a
valuable product, being employed in the manufacture of green and
blue pigments.

Other immediate results of the economical production of sulphuric
acid, are the general employment of phosphorus matches, and of
stearine candles, that beautiful substitute for tallow and wax.
Twenty-five years ago, the present prices and extensive applications
of sulphuric and muriatic acids, of soda, phosphorus, &c., would
have been considered utterly impossible. Who is able to foresee what
new and unthought-of chemical productions, ministering to the
service and comforts of mankind, the next twenty-five years may

After these remarks you will perceive that it is no exaggeration to
say, we may fairly judge of the commercial prosperity of a country
from the amount of sulphuric acid it consumes. Reflecting upon the
important influence which the price of sulphur exercises upon the
cost of production of bleached and printed cotton stuffs, soap,
glass, &c., and remembering that Great Britain supplies America,
Spain, Portugal, and the East, with these, exchanging them for raw
cotton, silk, wine, raisins, indigo, &c., &c., we can understand why
the English Government should have resolved to resort to war with
Naples, in order to abolish the sulphur monopoly, which the latter
power attempted recently to establish. Nothing could be more opposed
to the true interests of Sicily than such a monopoly; indeed, had it
been maintained a few years, it is highly probable that sulphur, the
source of her wealth, would have been rendered perfectly valueless
to her. Science and industry form a power to which it is dangerous
to present impediments. It was not difficult to perceive that the
issue would be the entire cessation of the exportation of sulphur
from Sicily. In the short period the sulphur monopoly lasted,
fifteen patents were taken out for methods to obtain back the
sulphuric acid used in making soda. Admitting that these fifteen
experiments were not perfectly successful, there can be no doubt it
would ere long have been accomplished. But then, in gypsum,
(sulphate of lime), and in heavy-spar, (sulphate of barytes), we
possess mountains of sulphuric acid; in galena, (sulphate of lead),
and in iron pyrites, we have no less abundance of sulphur. The
problem is, how to separate the sulphuric acid, or the sulphur, from
these native stores. Hundreds of thousands of pounds weight of
sulphuric acid were prepared from iron pyrites, while the high price
of sulphur consequent upon the monopoly lasted. We should probably
ere long have triumphed over all difficulties, and have separated it
from gypsum. The impulse has been given, the possibility of the
process proved, and it may happen in a few years that the
inconsiderate financial speculation of Naples may deprive her of
that lucrative commerce. In like manner Russia, by her prohibitory
system, has lost much of her trade in tallow and potash. One country
purchases only from absolute necessity from another, which excludes
her own productions from her markets. Instead of the tallow and
linseed oil of Russia, Great Britain now uses palm oil and cocoa-nut
oil of other countries. Precisely analogous is the combination of
workmen against their employers, which has led to the construction
of many admirable machines for superseding manual labour. In
commerce and industry every imprudence carries with it its own
punishment; every oppression immediately and sensibly recoils upon
the head of those from whom it emanates.


My dear Sir,

One of the most influential causes of improvement in the social
condition of mankind is that spirit of enterprise which induces men
of capital to adopt and carry out suggestions for the improvement of
machinery, the creation of new articles of commerce, or the cheaper
production of those already in demand; and we cannot but admire the
energy with which such men devote their talents, their time, and
their wealth, to realise the benefits of the discoveries and
inventions of science. For even when these are expended upon objects
wholly incapable of realisation,--nay, even when the idea which
first gave the impulse proves in the end to be altogether
impracticable or absurd, immediate good to the community generally
ensues; some useful and perhaps unlooked-for result flows directly,
or springs ultimately, from exertions frustrated in their main
design. Thus it is also in the pursuit of science. Theories lead to
experiments and investigations; and he who investigates will
scarcely ever fail of being rewarded by discoveries. It may be,
indeed, the theory sought to be established is entirely unfounded in
nature; but while searching in a right spirit for one thing, the
inquirer may be rewarded by finding others far more valuable than
those which he sought.

At the present moment, electro-magnetism, as a moving power, is
engaging great attention and study; wonders are expected from its
application to this purpose. According to the sanguine expectations
of many persons, it will shortly be employed to put into motion
every kind of machinery, and amongst other things it will be applied
to impel the carriages of railroads, and this at so small a cost,
that expense will no longer be matter of consideration. England is
to lose her superiority as a manufacturing country, inasmuch as her
vast store of coals will no longer avail her as an economical source
of motive power. "We," say the German cultivators of this science,
"have cheap zinc, and, how small a quantity of this metal is
required to turn a lathe, and consequently to give motion to any
kind of machinery!"

Such expectations may be very attractive, and yet they are
altogether illusory! they will not bear the test of a few simple
calculations; and these our friends have not troubled themselves to

With a simple flame of spirits of wine, under a proper vessel
containing boiling water, a small carriage of 200 to 300 pounds
weight can be put into motion, or a weight of 80 to 100 pounds may
be raised to a height of 20 feet. The same effects may be produced
by dissolving zinc in dilute sulphuric acid in a certain apparatus.
This is certainly an astonishing and highly interesting discovery;
but the question to be determined is, which of the two processes is
the least expensive?

In order to answer this question, and to judge correctly of the
hopes entertained from this discovery, let me remind you of what
chemists denominate "equivalents." These are certain unalterable
ratios of effects which are proportionate to each other, and may
therefore be expressed in numbers. Thus, if we require 8 pounds of
oxygen to produce a certain effect, and we wish to employ chlorine
for the same effect, we must employ neither more nor less than 35
1/2 pounds weight. In the same manner, 6 pounds weight of coal are
equivalent to 32 pounds weight of zinc. The numbers representing
chemical equivalents express very general ratios of effects,
comprehending for all bodies all the actions they are capable of

If zinc be combined in a certain manner with another metal, and
submitted to the action of dilute sulphuric acid, it is dissolved in
the form of an oxide; it is in fact burned at the expense of the
oxygen contained in the fluid. A consequence of this action is the
production of an electric current, which, if conducted through a
wire, renders it magnetic. In thus effecting the solution of a pound
weight, for example, of zinc, we obtain a definite amount of force
adequate to raise a given weight one inch, and to keep it suspended;
and the amount of weight it will be capable of suspending will be
the greater the more rapidly the zinc is dissolved.

By alternately interrupting and renewing the contact of the zinc
with the acid, and by very simple mechanical arrangements, we can
give to the iron an upward and downward or a horizontal motion, thus
producing the conditions essential to the motion of any machinery.

This moving force is produced by the oxidation of the zinc; and,
setting aside the name given to the force in this case, we know that
it can be produced in another manner. If we burn the zinc under the
boiler of a steam-engine, consequently in the oxygen of the air
instead of the galvanic pile, we should produce steam, and by it a
certain amount of force. If we should assume, (which, however, is
not proved,) that the quantity of force is unequal in these
cases,--that, for instance, we had obtained double or triple the
amount in the galvanic pile, or that in this mode of generating
force less loss is sustained,--we must still recollect the
equivalents of zinc and coal, and make these elements of our
calculation. According to the experiments of Despretz, 6 pounds
weight of zinc, in combining with oxygen, develops no more heat than
1 pound of coal; consequently, under equal conditions, we can
produce six times the amount of force with a pound of coal as with a
pound of zinc. It is therefore obvious that it would be more
advantageous to employ coal instead of zinc, even if the latter
produced four times as much force in a galvanic pile, as an equal
weight of coal by its combustion under a boiler. Indeed it is highly
probable, that if we burn under the boiler of a steam-engine the
quantity of coal required for smelting the zinc from its ores, we
shall produce far more force than the whole of the zinc so obtained
could originate in any form of apparatus whatever.

Heat, electricity, and magnetism, have a similar relation to each
other as the chemical equivalents of coal, zinc, and oxygen. By a
certain measure of electricity we produce a corresponding proportion
of heat or of magnetic power; we obtain that electricity by chemical
affinity, which in one shape produces heat, in another electricity
or magnetism. A certain amount of affinity produces an equivalent of
electricity in the same manner as, on the other hand, we decompose
equivalents of chemical compounds by a definite measure of
electricity. The magnetic force of the pile is therefore limited to
the extent of the chemical affinity, and in the case before us is
obtained by the combination of the zinc and sulphuric acid. In the
combustion of coal, the heat results from, and is measured by, the
affinity of the oxygen of the atmosphere for that substance.

It is true that with a very small expense of zinc, we can make an
iron wire a magnet capable of sustaining a thousand pounds weight of
iron; let us not allow ourselves to be misled by this. Such a magnet
could not raise a single pound weight of iron two inches, and
therefore could not impart motion. The magnet acts like a rock,
which while at rest presses with a weight of a thousand pounds upon
a basis; it is like an inclosed lake, without an outlet and without
a fall. But it may be said, we have, by mechanical arrangements,
given it an outlet and a fall. True; and this must be regarded as a
great triumph of mechanics; and I believe it is susceptible of
further improvements, by which greater force may be obtained. But
with every conceivable advantage of mechanism, no one will dispute
that one pound of coal, under the boiler of a steam-engine, will
give motion to a mass several hundred times greater than a pound of
zinc in the galvanic pile.

Our experience of the employment of electro-magnetism as a motory
power is, however, too recent to enable us to foresee the ultimate
results of contrivances to apply it; and, therefore, those who have
devoted themselves to solve the problem of its application should
not be discouraged, inasmuch as it would undoubtedly be a most
important achievement to supersede the steam-engine, and thus escape
the danger of railroads, even at double their expense.

Professor Weber of Gottingen has thrown out a suggestion, that if a
contrivance could be devised to enable us to convert at will the
wheels of the steam-carriage into magnets, we should be enabled to
ascend and descend acclivities with great facility. This notion may
ultimately be, to a certain extent, realised.

The employment of the galvanic pile as a motory power, however,
must, like every other contrivance, depend upon the question of its
relative economy: probably some time hence it may so far succeed as
to be adopted in certain favourable localities; it may stand in the
same relation to steam power as the manufacture of beet sugar bears
to that of cane, or as the production of gas from oils and resins to
that from mineral coal.

The history of beet-root sugar affords us an excellent illustration
of the effect of prices upon commercial productions. This branch of
industry seems at length, as to its processes, to be perfected. The
most beautiful white sugar is now manufactured from the beet-root,
in the place of the treacle-like sugar, having the taste of the
root, which was first obtained; and instead of 3 or 4 per cent., the
proportion obtained by Achard, double or even treble that amount is
now produced. And notwithstanding the perfection of the manufacture,
it is probable it will ere long be in most places entirely
discontinued. In the years 1824 to 1827, the prices of agricultural
produce were much lower than at present, while the price of sugar
was the same. At that time one malter [1] of wheat was 10s., and one
klafter [2] of wood 18s., and land was falling in price. Thus, food
and fuel were cheap, and the demand for sugar unlimited; it was,
therefore, advantageous to grow beet-root, and to dispose of the
produce of land as sugar. All these circumstances are now different.
A malter of wheat costs 18s.; a klafter of wood, 30s. to 36s. Wages
have risen, but not in proportion, whilst the price of colonial
sugar has fallen. Within the limits of the German commercial league,
as, for instance, at Frankfort-on-the-Maine, a pound of the whitest
and best loaf sugar is 7d.; the import duty is 31/d., or 30s. per
cwt., leaving 31/d. as the price of the sugar. In the year 1827,
then, one malter of wheat was equal to 40 lbs. weight of sugar,
whilst at present that quantity of wheat is worth 70 lbs. of sugar.
If indeed fuel were the same in price as formerly, and 70 lbs. of
sugar could be obtained from the same quantity of the root as then
yielded 40 lbs., it might still be advantageously produced; but the
amount, if now obtained by the most approved methods of extraction,
falls far short of this; and as fuel is double the price, and labour
dearer, it follows that, at present, it is far more advantageous to
cultivate wheat and to purchase sugar.

There are, however, other elements which must enter into our
calculations; but these serve to confirm our conclusion that the
manufacture of beet-root sugar as a commercial speculation must
cease. The leaves and residue of the root, after the juice was
expressed, were used as food for cattle, and their value naturally
increased with the price of grain. By the process formerly pursued,
75 lbs. weight of juice were obtained from 100 lbs. of beet-root,
and gave 5 lbs. of sugar. The method of Schutzenbach, which was
eagerly adopted by the manufacturers, produced from the same
quantity of root 8 lbs. of sugar; but it was attended with more
expense to produce, and the loss of the residue as food for cattle.
The increased expense in this process arises from the larger
quantity of fuel required to evaporate the water; for instead of
merely evaporating the juice, the dry residue is treated with water,
and we require fuel sufficient to evaporate 106 lbs. of fluid
instead of 75 lbs., and the residue is only fit for manure. The
additional 3 lbs. of sugar are purchased at the expense of much
fuel, and the loss of the residue as an article of food.

If the valley of the Rhine possessed mines of diamonds as rich as
those of Golconda, Visiapoor, or the Brazils, they would probably
not be worth the working: at those places the cost of extraction is
28s. to 30s. the carat. With us it amounts to three or four times as
much--to more, in fact, than diamonds are worth in the market. The
sand of the Rhine contains gold; and in the Grand Duchy of Baden
many persons are occupied in gold-washing when wages are low; but as
soon as they rise, this employment ceases. The manufacture of sugar
from beet-root, in the like manner, twelve to fourteen years ago
offered advantages which are now lost: instead, therefore, of
maintaining it at a great sacrifice, it would be more reasonable,
more in accordance with true natural economy, to cultivate other and
more valuable productions, and with them purchase sugar. Not only
would the state be the gainer, but every member of the community.
This argument does not apply, perhaps, to France and Bohemia, where
the prices of fuel and of colonial sugar are very different to those
in Germany.

The manufacture of gas for lighting, from coal, resin, and oils,
stands with us on the same barren ground.

The price of the materials from which gas is manufactured in England
bears a direct proportion to the price of corn: there the cost of
tallow and oil is twice as great as in Germany, but iron and coal
are two-thirds cheaper; and even in England the manufacture of gas
is only advantageous when the other products of the distillation of
coal, the coke, &c., can be sold.

It would certainly be esteemed one of the greatest discoveries of
the age if any one could succeed in condensing coal gas into a
white, dry, solid, odourless substance, portable, and capable of
being placed upon a candlestick, or burned in a lamp. Wax, tallow,
and oil, are combustible gases in a solid or fluid form, which offer
many advantages for lighting, not possessed by gas: they furnish, in
well-constructed lamps, as much light, without requiring the
expensive apparatus necessary for the combustion of gas, and they
are generally more economical. In large towns, or such
establishments as hotels, where coke is in demand, and where losses
in stolen tallow or oil must be considered, together with the labour
of snuffing candles and cleaning lamps, the higher price of gas is
compensated. In places where gas can be manufactured from resin, oil
of turpentine, and other cheap oils, as at Frankfort, this is
advantageous so long as it is pursued on small scale only. If large
towns were lighted in the same manner, the materials would rise in
price: the whole amount at present produced would scarcely suffice
for two such towns as Berlin and Munich. But no just calculation can
be made from the present prices of turpentine, resin, &c., which are
not produced upon any large scale.

[Footnote 1: Malter--a measure containing several bushels, but
varying in different countries.]

[Footnote 2: Klafter--a cord, a stack, measuring six feet every


My dear Sir,

Until very recently it was supposed that the physical qualities of
bodies, i.e. hardness, colour, density, transparency, &c., and still
more their chemical properties, must depend upon the nature of their
elements, or upon their composition. It was tacitly received as a
principle, that two bodies containing the same elements in the same
proportion, must of necessity possess the same properties. We could
not imagine an exact identity of composition giving rise to two
bodies entirely different in their sensible appearance and chemical
relations. The most ingenious philosophers entertained the opinion
that chemical combination is an inter-penetration of the particles
of different kinds of matter, and that all matter is susceptible of
infinite division. This has proved to be altogether a mistake. If
matter were infinitely divisible in this sense, its particles must
be imponderable, and a million of such molecules could not weigh
more than an infinitely small one. But the particles of that
imponderable matter, which, striking upon the retina, give us the
sensation of light, are not in a mathematical sense infinitely

Inter-penetration of elements in the production of a chemical
compound, supposes two distinct bodies, A and B, to occupy one and
the same space at the same time. If this were so, different
properties could not consist with an equal and identical

That hypothesis, however, has shared the fate of innumerable
imaginative explanations of natural phenomena, in which our
predecessors indulged. They have now no advocate. The force of
truth, dependent upon observation, is irresistible. A great many
substances have been discovered amongst organic bodies, composed of
the same elements in the same relative proportions, and yet
exhibiting physical and chemical properties perfectly distinct one
from another. To such substances the term Isomeric (from 1/ao1/
equal and aei1/o1/ part) is applied. A great class of bodies, known
as the volatile oils, oil of turpentine, essence of lemons, oil of
balsam of copaiba, oil of rosemary, oil of juniper, and many others,
differing widely from each other in their odour, in their medicinal
effects, in their boiling point, in their specific gravity, &c., are
exactly identical in composition,--they contain the same elements,
carbon and hydrogen, in the same proportions.

How admirably simple does the chemistry of organic nature present
itself to us from this point of view! An extraordinary variety of
compound bodies produced with equal weights of two elements! and how
wide their dissimilarity! The crystallised part of the oil of roses,
the delicious fragrance of which is so well known, a solid at
ordinary temperatures, although readily volatile, is a compound body
containing exactly the same elements, and in the same proportions,
as the gas we employ for lighting our streets; and, in short, the
same elements, in the same relative quantities, are found in a dozen
other compounds, all differing essentially in their physical and
chemical properties.

These remarkable truths, so highly important in their applications,
were not received and admitted as sufficiently established, without
abundant proofs. Many examples have long been known where the
analysis of two different bodies gave the same composition; but such
cases were regarded as doubtful: at any rate, they were isolated
observations, homeless in the realms of science: until, at length,
examples were discovered of two or more bodies whose absolute
identity of composition, with totally distinct properties, could be
demonstrated in a more obvious and conclusive manner than by mere
analysis; that is, they can be converted and reconverted into each
other without addition and without subtraction.

In cyanuric acid, hydrated cyanic acid, and cyamelide, we have three
such isomeric compounds.

Cyanuric acid is crystalline, soluble in water, and capable of
forming salts with metallic oxides.

Hydrated cyanic acid is a volatile and highly blistering fluid,
which cannot be brought into contact with water without being
instantaneously decomposed.

Cyamelide is a white substance very like porcelain, absolutely
insoluble in water.

Now if we place the first,--cyanuric acid,--in a vessel hermetically
sealed, and apply a high degree of heat, it is converted by its
influence into hydrated cyanic acid; and, then, if this is kept for
some time at the common temperature, it passes into cyamelide, no
other element being present. And, again inversely, cyamelide can be
converted into cyanuric acid and hydrated cyanic acid.

We have three other bodies which pass through similar changes, in
aldehyde, metaldehyde, and etaldehyde; and, again two, in urea and
cyanuret of ammonia. Further, 100 parts of aldehyde hydrated butyric
acid and acetic ether contain the same elements in the same
proportion. Thus one substance may be converted into another without
addition or subtraction, and without the participation of any
foreign bodies in the change.

The doctrine that matter is not infinitely divisible, but on the
contrary, consists of atoms incapable of further division, alone
furnishes us with a satisfactory explanation of these phenomena. In
chemical combinations, the ultimate atoms of bodies do not penetrate
each other, they are only arranged side by side in a certain order,
and the properties of the compound depend entirely upon this order.
If they are made to change their place--their mode of
arrangement--by an impulse from without, they combine again in a
different manner, and another compound is formed with totally
different properties. We may suppose that one atom combines with one
atom of another element to form a compound atom, while in other
bodies two and two, four and four, eight and eight, are united; so
that in all such compounds the amount per cent. of the elements is
absolutely equal; and yet their physical and chemical properties
must be totally different, the constitution of each atom being
peculiar, in one body consisting of two, in another of four, in a
third of eight, and in a fourth of sixteen simple atoms.

The discovery of these facts immediately led to many most beautiful
and interesting results; they furnished us with a satisfactory
explanation of observations which were before veiled in mystery,--a
key to many of Nature's most curious recesses.

Again; solid bodies, whether simple or compound, are capable of
existing in two states, which are known by the terms amorphous and

When matter is passing from a gaseous or liquid state slowly into a
solid, an incessant motion is observed, as if the molecules were
minute magnets; they are seen to repel each other in one direction,
and to attract and cohere together in another, and in the end become
arranged into a regular form, which under equal circumstances is
always the same for any given kind of matter; that is, crystals are

Time and freedom of motion for the particles of bodies are necessary
to the formation of crystals. If we force a fluid or a gas to become
suddenly solid, leaving no time for its particles to arrange
themselves, and cohere in that direction in which the cohesive
attraction is strongest, no crystals will be formed, but the
resulting solid will have a different colour, a different degree of
hardness and cohesion, and will refract light differently; in one
word, will be amorphous. Thus we have cinnabar as a red and a
jet-black substance; sulphur a fixed and brittle body, and soft,
semitransparent, and ductile; glass as a milk-white opaque
substance, so hard that it strikes fire with steel, and in its
ordinary and well-known state. These dissimilar states and
properties of the same body are occasioned in one case by a regular,
in the other by an irregular, arrangement of its atoms; one is
crystalline, the other amorphous.

Applying these facts to natural productions, we have reason to
believe that clay-slate, and many kinds of greywacke, are amorphous
feldspar, as transition limestone is amorphous marble, basalt and
lava mixtures of amorphous zeolite and augite. Anything that
influences the cohesion, must also in a certain degree alter the
properties of bodies. Carbonate of lime, if crystallised at ordinary
temperatures, possesses the crystalline form, hardness, and
refracting power of common spar; if crystallised at a higher
temperature, it has the form and properties of arragonite.

Finally, Isomorphism, or the equality of form of many chemical
compounds having a different composition, tends to prove that matter
consists of atoms the mere arrangement of which produces all the
properties of bodies. But when we find that a different arrangement
of the same elements gives rise to various physical and chemical
properties, and a similar arrangement of different elements produces
properties very much the same, may we not inquire whether some of
those bodies which we regard as elements may not be merely
modifications of the same substance?--whether they are not the same
matter in a different state of arrangement? We know in fact the
existence of iron in two states, so dissimilar, that in the one, it
is to the electric chain like platinum, and in the other it is like
zinc; so that powerful galvanic machines have been constructed of
this one metal.

Among the elements are several instances of remarkable similarity of
properties. Thus there is a strong resemblance between platinum and
iridium; bromine and iodine; iron, manganese, and magnesium; cobalt
and nickel; phosphorus and arsenic; but this resemblance consists
mainly in their forming isomorphous compounds in which these
elements exist in the same relative proportion. These compounds are
similar, because the atoms of which they are composed are arranged
in the same manner. The converse of this is also true: nitrate of
strontia becomes quite dissimilar to its common state if a certain
proportion of water is taken into its composition.

If we suppose selenium to be merely modified sulphur, and phosphorus
modified arsenic, how does it happen, we must inquire, that
sulphuric acid and selenic acid, phosphoric and arsenic acid,
respectively form compounds which it is impossible to distinguish by
their form and solubility? Were these merely isomeric, they ought to
exhibit properties quite dissimilar!

We have not, I believe, at present the remotest ground to suppose
that any one of those substances which chemists regard as elements
can be converted into another. Such a conversion, indeed, would
presuppose that the element was composed of two or more ingredients,
and was in fact not an element; and until the decomposition of these
bodies is accomplished, and their constituents discovered, all
pretensions to such conversions deserve no notice.

Dr. Brown of Edinburgh thought he had converted iron into rhodium,
and carbon or paracyanogen into silicon. His paper upon this subject
was published in the Transactions of the Royal Society of Edinburgh,
and contained internal evidence, without a repetition of his
experiments, that he was totally unacquainted with the principles of
chemical analysis. But his experiments have been carefully repeated
by qualified persons, and they have completely proved his ignorance:
his rhodium is iron, and his silicon an impure incombustible coal.


My dear Sir,

One of the most remarkable effects of the recent progress of science
is the alliance of chemistry with physiology, by which a new and
unexpected light has been thrown upon the vital processes of plants
and animals. We have now no longer any difficulty in understanding
the different actions of aliments, poisons, and remedial agents--we
have a clear conception of the causes of hunger, of the exact nature
of death; and we are not, as formerly, obliged to content ourselves
with a mere description of their symptoms. It is now ascertained
with positive certainty, that all the substances which constitute
the food of man must be divided into two great classes, one of which
serves for the nutrition and reproduction of the animal body, whilst
the other ministers to quite different purposes. Thus starch, gum,
sugar, beer, wine, spirits, &c., furnish no element capable of
entering into the composition of blood, muscular fibre, or any part
which is the seat of the vital principle. It must surely be
universally interesting to trace the great change our views have
undergone upon these subjects, as well as to become acquainted with
the researches from which our present knowledge is derived.

The primary conditions of the maintenance of animal life, are a
constant supply of certain matters, animal food, and of oxygen, in
the shape of atmospheric air. During every moment of life, oxygen is
absorbed from the atmosphere in the organs of respiration, and the
act of breathing cannot cease while life continues.

The observations of physiologists have demonstrated that the body of
an adult man supplied abundantly with food, neither increases nor
diminishes in weight during twenty-four hours, and yet the quantity
of oxygen absorbed into his system, in that period, is very
considerable. According to the experiments of Lavoisier, an adult
man takes into his system from the atmosphere, in one year, no less
than 746 pounds weight of oxygen; the calculations of Menzies make
the quantity amount even to 837 pounds; but we find his weight at
the end of the year either exactly the same or different one way or
the other by at most a few pounds. What, it may be asked, has become
of the enormous amount of oxygen thus introduced into the human
system in the course of one year? We can answer this question
satisfactorily. No part of the oxygen remains in the body, but is
given out again, combined with carbon and hydrogen. The carbon and
hydrogen of certain parts of the animal body combine with the oxygen
introduced through the lungs and skin, and pass off in the forms of
carbonic acid and vapour of water. At every expiration and every
moment of life, a certain amount of its elements are separated from
the animal organism, having entered into combination with the oxygen
of the atmosphere.

In order to obtain a basis for the approximate calculation, we may
assume, with Lavoisier and Seguin, that an adult man absorbs into
his system 32 1/2 ounces of oxygen daily,--that is, 46,037 cubic
inches = 15,661 grains, French weight; and further, that the weight
of the whole mass of his blood is 24 pounds, of which 80 per cent.
is water. Now, from the known composition of the blood, we know that
in order to convert its whole amount of carbon and hydrogen into
carbonic acid and water, 64.102 grains of oxygen are required. This
quantity will be taken into the system in four days and five hours.
Whether the oxygen enters into combination directly with the
elements of the blood, or with the carbon and hydrogen of other
parts of the body, it follows inevitably--the weight of the body
remaining unchanged and in a normal condition--that as much of these
elements as will suffice to supply 24 pounds of blood, must be taken
into the system in four days and five hours; and this necessary
amount is furnished by the food.

We have not, however, remained satisfied with mere approximation: we
have determined accurately, in certain cases, the quantity of carbon
taken daily in the food, and of that which passes out of the body in
the faeces and urine combined--that is, uncombined with oxygen; and
from these investigations it appears that an adult man taking
moderate exercise consumes 13.9 ounces of carbon, which pass off
through the skin and lungs as carbonic acid gas. [1]

It requires 37 ounces of oxygen to convert 13 9/10 of carbon into
carbonic acid. Again; according to the analysis of Boussingault,
(Annales de Chim. et de Phys., lxx. i. p.136), a horse consumes 79
1/10 ounces of carbon in twenty-four hours, a milch cow 70 3/4
ounces; so that the horse requires 13 pounds 3 1/2 ounces, and the
cow 11 pounds 10 3/4 ounces of oxygen. [2]

As no part of the oxygen taken into the system of an animal is given
off in any other form than combined with carbon or hydrogen, and as
in a normal condition, or state of health, the carbon and hydrogen
so given off are replaced by those elements in the food, it is
evident that the amount of nourishment required by an animal for its
support must be in a direct ratio with the quantity of oxygen taken
in to its system. Two animals which in equal times take up by means
of the lungs and skin unequal quantities of oxygen, consume an
amount of food unequal in the same ratio. The consumption of oxygen
in a given time may be expressed by the number of respirations; it
is, therefore, obvious that in the same animal the quantity of
nourishment required must vary with the force and number of
respirations. A child breathes quicker than an adult, and,
consequently, requires food more frequently and proportionably in
larger quantity, and bears hunger less easily. A bird deprived of
food dies on the third day, while a serpent, confined under a bell,
respires so slowly that the quantity of carbonic acid generated in
an hour can scarcely be observed, and it will live three months, or
longer, without food. The number of respirations is fewer in a state
of rest than during labour or exercise: the quantity of food
necessary in both cases must be in the same ratio. An excess of
food, a want of a due amount of respired oxygen, or of exercise, as
also great exercise (which obliges us to take an increased supply of
food), together with weak organs of digestion, are incompatible with

But the quantity of oxygen received by an animal through the lungs
not only depends upon the number of respirations, but also upon the
temperature of the respired air. The size of the thorax of an animal
is unchangeable; we may therefore regard the volume of air which
enters at every inspiration as uniform. But its weight, and
consequently the amount of oxygen it contains, is not constant. Air
is expanded by heat, and contracted by cold--an equal volume of hot
and cold air contains, therefore, an unequal amount of oxygen. In
summer atmospheric air contains water in the form of vapour, it is
nearly deprived of it in winter; the volume of oxygen in the same
volume of air is smaller in summer than in winter. In summer and
winter, at the pole and at the equator, we inspire an equal volume
of air; the cold air is warmed during respiration and acquires the
temperature of the body. In order, therefore, to introduce into the
lungs a given amount of oxygen, less expenditure of force is
necessary in winter than in summer, and for the same expenditure of
force more oxygen is inspired in winter. It is also obvious that in
an equal number of respirations we consume more oxygen at the level
of the sea than on a mountain.

The oxygen taken into the system is given out again in the same
form, both in summer and winter: we expire more carbon at a low than
at a high temperature, and require more or less carbon in our food
in the same proportion; and, consequently, more is respired in
Sweden than in Sicily, and in our own country and eighth more in
winter than in summer. Even if an equal weight of food is consumed
in hot and cold climates, Infinite Wisdom has ordained that very
unequal proportions of carbon shall be taken in it. The food
prepared for the inhabitants of southern climes does not contain in
a fresh state more than 12 per cent. of carbon, while the blubber
and train oil which feed the inhabitants of Polar regions contain 66
to 80 per cent. of that element.

From the same cause it is comparatively easy to be temperate in warm
climates, or to bear hunger for a long time under the equator; but
cold and hunger united very soon produce exhaustion.

The oxygen of the atmosphere received into the blood in the lungs,
and circulated throughout every part of the animal body, acting upon
the elements of the food, is the source of animal heat.

[Footnote 1: This account is deduced from observations made upon the
average daily consumption of about 30 soldiers in barracks. The food
of these men, consisting of meat, bread, potatoes, lentils, peas,
beans, butter, salt, pepper, &c., was accurately weighed during a
month, and each article subjected to ultimate analysis. Of the
quantity of food, beer, and spirits, taken by the men when out of
barracks, we have a close approximation from the report of the
sergeant; and from the weight and analysis of the faeces and urine,
it appears that the carbon which passes off through these channels
may be considered equivalent to the amount taken in that portion of
the food, and of sour-crout, which was not included in the

[Footnote 2: 17.5 ounces = 0.5 kilogramme.]


My dear Sir,

The source of animal heat, its laws, and the influence it exerts
upon the functions of the animal body, constitute a curious and
highly interesting subject, to which I would now direct your

All living creatures, whose existence depends upon the absorption of
oxygen, possess within themselves a source of heat, independent of
surrounding objects.

This general truth applies to all animals, and extends to the seed
of plants in the act of germination, to flower-buds when developing,
and fruits during their maturation.

In the animal body, heat is produced only in those parts to which
arterial blood, and with it the oxygen absorbed in respiration, is
conveyed. Hair, wool, and feathers, receive no arterial blood, and,
therefore, in them no heat is developed. The combination of a
combustible substance with oxygen is, under all circumstances, the
only source of animal heat. In whatever way carbon may combine with
oxygen, the act of combination is accompanied by the disengagement
of heat. It is indifferent whether this combination takes place
rapidly or slowly, at a high or at a low temperature: the amount of
heat liberated is a constant quantity.

The carbon of the food, being converted into carbonic acid within
the body, must give out exactly as much heat as if it had been
directly burnt in oxygen gas or in common air; the only difference
is, the production of the heat is diffused over unequal times. In
oxygen gas the combustion of carbon is rapid and the heat intense;
in atmospheric air it burns slower and for a longer time, the
temperature being lower; in the animal body the combination is still
more gradual, and the heat is lower in proportion.

It is obvious that the amount of heat liberated must increase or
diminish with the quantity of oxygen introduced in equal times by
respiration. Those animals, therefore, which respire frequently, and
consequently consume much oxygen, possess a higher temperature than
others, which, with a body of equal size to be heated, take into the
system less oxygen. The temperature of a child (102 deg) is higher
than that of an adult (99 1/2 deg). That of birds (104 deg to 105.4
deg) is higher than that of quadrupeds (98 1/2 deg to 100.4 deg) or
than that of fishes or amphibia, whose proper temperature is from
2.7 to 3.6 deg higher than that of the medium in which they live.
All animals, strictly speaking, are warm-blooded; but in those only
which possess lungs is the temperature of the body quite independent
of the surrounding medium.

The most trustworthy observations prove that in all climates, in the
temperate zones as well as at the equator or the poles, the
temperature of the body in man, and in what are commonly called
warm-blooded animals, is invariably the same; yet how different are
the circumstances under which they live!

The animal body is a heated mass, which bears the same relation to
surrounding objects as any other heated mass. It receives heat when
the surrounding objects are hotter, it loses heat when they are
colder, than itself.

We know that the rapidity of cooling increases with the difference
between the temperature of the heated body and that of the
surrounding medium; that is, the colder the surrounding medium the
shorter the time required for the cooling of the heated body.

How unequal, then, must be the loss of heat in a man at Palermo,
where the external temperature is nearly equal to that of the body,
and in the polar regions, where the external temperature is from 70
deg to 90 deg lower!

Yet, notwithstanding this extremely unequal loss of heat, experience
has shown that the blood of the inhabitant of the arctic circle has
a temperature as high as that of the native of the south, who lives
in so different a medium.

This fact, when its true significance is perceived, proves that the
heat given off to the surrounding medium is restored within the body
with great rapidity. This compensation must consequently take place
more rapidly in winter than in summer, at the pole than at the

Now, in different climates the quantity of oxygen introduced into
the system by respiration, as has been already shown, varies
according to the temperature of the external air; the quantity of
inspired oxygen increases with the loss of heat by external cooling,
and the quantity of carbon or hydrogen necessary to combine with
this oxygen must be increased in the same ratio.

It is evident that the supply of the heat lost by cooling is
effected by the mutual action of the elements of the food and the
inspired oxygen, which combine together. To make use of a familiar,
but not on that account a less just illustration, the animal body
acts, in this respect, as a furnace, which we supply with fuel. It
signifies nothing what intermediate forms food may assume, what
changes it may undergo in the body; the last change is uniformly the
conversion of its carbon into carbonic acid, and of its hydrogen
into water. The unassimilated nitrogen of the food, along with the
unburned or unoxidised carbon, is expelled in the urine or in the
solid excrements. In order to keep up in the furnace a constant
temperature, we must vary the supply of fuel according to the
external temperature, that is, according to the supply of oxygen.

In the animal body the food is the fuel; with a proper supply of
oxygen we obtain the heat given out during its oxidation or
combustion. In winter, when we take exercise in a cold atmosphere,
and when consequently the amount of inspired oxygen increases, the
necessity for food containing carbon and hydrogen increases in the
same ratio; and by gratifying the appetite thus excited, we obtain
the most efficient protection against the most piercing cold. A
starving man is soon frozen to death. The animals of prey in the
arctic regions, as every one knows, far exceed in voracity those of
the torrid zone.

In cold and temperate climates, the air, which incessantly strives
to consume the body, urges man to laborious efforts in order to
furnish the means of resistance to its action, while, in hot
climates, the necessity of labour to provide food is far less

Our clothing is merely an equivalent for a certain amount of food.
The more warmly we are clothed the less urgent becomes the appetite
for food, because the loss of heat by cooling, and consequently the
amount of heat to be supplied by the food, is diminished.

If we were to go naked, like certain savage tribes, or if in hunting
or fishing we were exposed to the same degree of cold as the
Samoyedes, we should be able with ease to consume 10 lbs. of flesh,
and perhaps a dozen of tallow candles into the bargain, daily, as
warmly clad travellers have related with astonishment of these
people. We should then also be able to take the same quantity of
brandy or train oil without bad effects, because the carbon and
hydrogen of these substances would only suffice to keep up the
equilibrium between the external temperature and that of our bodies.

According to the preceding expositions, the quantity of food is
regulated by the number of respirations, by the temperature of the
air, and by the amount of heat given off to the surrounding medium.

No isolated fact, apparently opposed to this statement, can affect
the truth of this natural law. Without temporary or permanent injury
to health, the Neapolitan cannot take more carbon and hydrogen in
the shape of food than he expires as carbonic acid and water; and
the Esquimaux cannot expire more carbon and hydrogen than he takes
in the system as food, unless in a state of disease or of
starvation. Let us examine these states a little more closely.

The Englishman in Jamaica perceives with regret the disappearance of
his appetite, previously a source of frequently recurring enjoyment;
and he succeeds, by the use of cayenne pepper, and the most powerful
stimulants, in enabling himself to take as much food as he was
accustomed to eat at home. But the whole of the carbon thus
introduced into the system is not consumed; the temperature of the
air is too high, and the oppressive heat does not allow him to
increase the number of respirations by active exercise, and thus to
proportion the waste to the amount of food taken; disease of some
kind, therefore, ensues.

On the other hand, England sends her sick to southern regions, where
the amount of the oxygen inspired is diminished in a very large
proportion. Those whose diseased digestive organs have in a greater
or less degree lost the power of bringing the food into the state
best adapted for oxidation, and therefore are less able to resist
the oxidising influence of the atmosphere of their native climate,
obtain a great improvement in health. The diseased organs of
digestion have power to place the diminished amount of food in
equilibrium with the inspired oxygen, in the mild climate; whilst in
a colder region the organs of respiration themselves would have been
consumed in furnishing the necessary resistance to the action of the
atmospheric oxygen.

In our climate, hepatic diseases, or those arising from excess of
carbon, prevail in summer; in winter, pulmonary diseases, or those
arising from excess of oxygen, are more frequent.

The cooling of the body, by whatever cause it may be produced,
increases the amount of food necessary. The mere exposure to the
open air, in a carriage or on the deck of a ship, by increasing
radiation and vaporisation, increases the loss of heat, and compels
us to eat more than usual. The same is true of those who are
accustomed to drink large quantities of cold water, which is given
off at the temperature of the body, 98 1/2 deg. It increases the
appetite, and persons of weak constitution find it necessary, by
continued exercise, to supply to the system the oxygen required to
restore the heat abstracted by the cold water. Loud and long
continued speaking, the crying of infants, moist air, all exert a
decided and appreciable influence on the amount of food which is

We have assumed that carbon and hydrogen especially, by combining
with oxygen, serve to produce animal heat. In fact, observation
proves that the hydrogen of the food plays a no less important part
than the carbon.

The whole process of respiration appears most clearly developed,
when we consider the state of a man, or other animal, totally
deprived of food.

The first effect of starvation is the disappearance of fat, and this
fat cannot be traced either in the urine or in the scanty faeces.
Its carbon and hydrogen have been given off through the skin and
lungs in the form of oxidised products; it is obvious that they have
served to support respiration.

In the case of a starving man, 32 1/2 oz. of oxygen enter the system
daily, and are given out again in combination with a part of his
body. Currie mentions the case of an individual who was unable to
swallow, and whose body lost 100 lbs. in weight during a month; and,
according to Martell (Trans. Linn. Soc., vol. xi. p.411), a fat pig,
overwhelmed in a slip of earth, lived 160 days without food, and was
found to have diminished in weight, in that time, more than 120 lbs.
The whole history of hybernating animals, and the well-established
facts of the periodical accumulation, in various animals, of fat,
which, at other periods, entirely disappears, prove that the oxygen,
in the respiratory process, consumes, without exception, all such
substances as are capable of entering into combination with it. It
combines with whatever is presented to it; and the deficiency of
hydrogen is the only reason why carbonic acid is the chief product;
for, at the temperature of the body, the affinity of hydrogen for
oxygen far surpasses that of carbon for the same element.

We know, in fact, that the graminivora expire a volume of carbonic
acid equal to that of the oxygen inspired, while the carnivora, the
only class of animals whose food contains fat, inspire more oxygen
than is equal in volume to the carbonic acid expired. Exact
experiments have shown, that in many cases only half the volume of
oxygen is expired in the form of carbonic acid. These observations
cannot be gainsaid, and are far more convincing than those arbitrary
and artificially produced phenomena, sometimes called experiments;
experiments which, made as too often they are, without regard to the
necessary and natural conditions, possess no value, and may be
entirely dispensed with; especially when, as in the present case,
Nature affords the opportunity for observation, and when we make a
rational use of that opportunity.

In the progress of starvation, however, it is not only the fat which
disappears, but also, by degrees all such of the solids as are
capable of being dissolved. In the wasted bodies of those who have
suffered starvation, the muscles are shrunk and unnaturally soft,
and have lost their contractibility; all those parts of the body
which were capable of entering into the state of motion have served
to protect the remainder of the frame from the destructive influence
of the atmosphere. Towards the end, the particles of the brain begin
to undergo the process of oxidation, and delirium, mania, and death
close the scene; that is to say, all resistance to the oxidising
power of the atmospheric oxygen ceases, and the chemical process of
eremacausis, or decay, commences, in which every part of the body,
the bones excepted, enters into combination with oxygen.

The time which is required to cause death by starvation depends on
the amount of fat in the body, on the degree of exercise, as in
labour or exertion of any kind, on the temperature of the air, and
finally, on the presence or absence of water. Through the skin and
lungs there escapes a certain quantity of water, and as the presence
of water is essential to the continuance of the vital motions, its
dissipation hastens death. Cases have occurred, in which a full
supply of water being accessible to the sufferer, death has not
occurred till after the lapse of twenty days. In one case, life was
sustained in this way for the period of sixty days.

In all chronic diseases death is produced by the same cause, namely,
the chemical action of the atmosphere. When those substances are
wanting, whose function in the organism is to support the process of
respiration, when the diseased organs are incapable of performing
their proper function of producing these substances, when they have
lost the power of transforming the food into that shape in which it
may, by entering into combination with the oxygen of the air,
protect the system from its influence, then, the substance of the
organs themselves, the fat of the body, the substance of the
muscles, the nerves, and the brain, are unavoidably consumed.

The true cause of death in these cases is the respiratory process,
that is, the action of the atmosphere.

A deficiency of food, and a want of power to convert the food into a
part of the organism, are both, equally, a want of resistance; and
this is the negative cause of the cessation of the vital process.
The flame is extinguished, because the oil is consumed; and it is
the oxygen of the air which has consumed it.

In many diseases substances are produced which are incapable of
assimilation. By the mere deprivation of food, these substances are
removed from the body without leaving a trace behind; their elements
have entered into combination with the oxygen of the air.

From the first moment that the function of the lungs or of the skin
is interrupted or disturbed, compounds, rich in carbon, appear in
the urine, which acquires a brown colour. Over the whole surface of
the body oxygen is absorbed, and combines with all the substances
which offer no resistance to it. In those parts of the body where
the access of oxygen is impeded; for example, in the arm-pits, or in
the soles of the feet, peculiar compounds are given out,
recognisable by their appearance, or by their odour. These compounds
contain much carbon.

Respiration is the falling weight--the bent spring, which keeps the
clock in motion; the inspirations and expirations are the strokes of
the pendulum which regulate it. In our ordinary time-pieces, we know
with mathematical accuracy the effect produced on their rate of
going, by changes in the length of the pendulum, or in the external
temperature. Few, however, have a clear conception of the influence
of air and temperature on the health of the human body; and yet the
research into the conditions necessary to keep it in the normal
state is not more difficult than in the case of a clock.


My dear Sir,

Having attempted in my last letter to explain to you the simple and
admirable office subserved by the oxygen of the atmosphere in its
combination with carbon in the animal body, I will now proceed to
present you with some remarks upon those materials which sustain its
mechanisms in motion, and keep up their various functions,--namely,
the Aliments.

If the increase in mass in an animal body, the development and
reproduction of its organs depend upon the blood, then those
substances only which are capable of being converted into blood can
be properly regarded as nourishment. In order then to ascertain what
parts of our food are nutritious, we must compare the composition of
the blood with the composition of the various articles taken as

Two substances require especial consideration as the chief
ingredients of the blood; one of these separates immediately from
the blood when it is withdrawn from the circulation.

It is well known that in this case blood coagulates, and separates
into a yellowish liquid, the serum of the blood, and a gelatinous
mass, which adheres to a rod or stick in soft, elastic fibres, when
coagulating blood is briskly stirred. This is the fibrine of the
blood, which is identical in all its properties with muscular fibre,
when the latter is purified from all foreign matters.

The second principal ingredient of the blood is contained in the
serum, and gives to this liquid all the properties of the white of
eggs, with which it is indeed identical. When heated, it coagulates
into a white elastic mass, and the coagulating substance is called

Fibrine and albumen, the chief ingredients of blood, contain, in
all, seven chemical elements, among which nitrogen, phosphorus, and
sulphur are found. They contain also the earth of bones. The serum
retains in solution sea salt and other salts of potash and soda, in
which the acids are carbonic, phosphoric, and sulphuric acids. The
globules of the blood contain fibrine and albumen, along with a red
colouring matter, in which iron is a constant element. Besides
these, the blood contains certain fatty bodies in small quantity,
which differ from ordinary fats in several of their properties.

Chemical analysis has led to the remarkable result, that fibrine and
albumen contain the same organic elements united in the same
proportion,--i.e., that they are isomeric, their chemical
composition--the proportion of their ultimate elements--being
identical. But the difference of their external properties shows
that the particles of which they are composed are arranged in a
different order. (See Letter V).

This conclusion has lately been beautifully confirmed by a
distinguished physiologist (Denis), who has succeeded in converting
fibrine into albumen, that is, in giving it the solubility, and
coagulability by heat, which characterise the white of egg.

Fibrine and albumen, besides having the same composition, agree also
in this, that both dissolve in concentrated muriatic acid, yielding
a solution of an intense purple colour. This solution, whether made
with fibrine or albumen, has the very same re-actions with all
substances yet tried.

Both albumen and fibrine, in the process of nutrition, are capable
of being converted into muscular fibre, and muscular fibre is
capable of being reconverted into blood. These facts have long been
established by physiologists, and chemistry has merely proved that
these metamorphoses can be accomplished under the influence of a
certain force, without the aid of a third substance, or of its
elements, and without the addition of any foreign element, or the
separation of any element previously present in these substances.

If we now compare the composition of all organised parts with that
of fibrine and albumen, the following relations present themselves:-

All parts of the animal body which have a decided shape, which form
parts of organs, contain nitrogen. No part of an organ which
possesses motion and life is destitute of nitrogen; all of them
contain likewise carbon and the elements of water; the latter,
however, in no case in the proportion to form water.

The chief ingredients of the blood contain nearly 17 per cent. of
nitrogen, and from numerous analyses it appears that no part of an
organ contains less than 17 per cent. of nitrogen.

The most convincing experiments and observations have proved that
the animal body is absolutely incapable of producing an elementary
body, such as carbon or nitrogen, out of substances which do not
contain it; and it obviously follows, that all kinds of food fit for
the production either of blood, or of cellular tissue, membranes,
skin, hair, muscular fibre, &c., must contain a certain amount of

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