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The Boy Mechanic: Volume 1 by Popular Mechanics

Part 4 out of 15

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The first thing to make is a molding bench, as shown in Fig. 1. It
is possible to make molds without a bench, but it is a mistake to
try to do this, as the sand is sure to get on the floor, whence it
is soon tracked into the house. The bench will also make the
operation of molding much easier and will prove to be a great

The bench should be made of lumber about 1 in. thick and should be
constructed in the form of a trough, as shown. Two cleats, AA,
should be nailed to the front and back to support the
cross-boards, BE, which in turn support the mold while it is being
made. The object of using the cleats and removable cross-boards
instead of a stationary shelf is to give access to the sand, C,
when it is being prepared.

About one or two cubic feet of fine molding-sand will be required,
which may, be purchased at the nearest foundry for a small sum.
Yellow sand will be found a little better for the amateur's work
than the black sand generally used in most foundries, but if no
yellow sand can be obtained the black kind will do. If there is no

[Illustration: Fig. 1 - Convenient Arrangement of Bench and Tools]

near at hand, try using sand from other sources, giving preference
to the finest sand and that which clings together in a cake when
compressed between the hands. Common lake or river sand is not
suitable for the purpose, as it is too coarse and will not make a
good mold.

For mixing and preparing the sand a small shovel, D, and a sieve,
E, will be required. If desired the sieve may be homemade.
Ordinary wire netting such as is used in screen doors, is about
the right mesh, and this, nailed to replace the bottom of a box,
makes a very good sieve.

The rammer, F, is made of wood, and is wedge-shaped at one end and
flat at the other, as shown. In foundries each molder generally
uses two rammers, but for the small work which will be described
one will be sufficient. An old teaspoon, G, will be found useful
in the molding operations and may be hung on the wall or other
convenient place when not in use.

The cloth bag, H, which can be made of a knitted stocking, is
filled with coal dust; which is used for a parting medium in
making the molds. Take a small lump of soft coal and reduce to
powder by pounding. Screen out all the coarse pieces and put the
remainder in the bag. A slight shake of the bag

[Illustration: Fig. 2; Homemade Flask]

over the mold will then cause a cloud of coal-dust to fall on it,
thus preventing the two layers of sand from sticking, but this
operation will be described more fully later on.

The flask, J, Fig. 1, is shown more clearly in Fig. 2. It is made
of wood and is in two halves, the "cope," or upper half, and the
"drag," or lower part. A good way to make the flask is to take a
box, say 12 in. by 8 in. by 6 in. high, and saw it in half
longitudinally, as shown. If the box is not very strong, the
corners should be braced with triangular wooden strips, A A, which
should be nailed in, previous to sawing. The wooden strips BB are
used to hold the sand, which would otherwise slide out of the
flask when the two halves of the mold are separated.

The dowels, CC, are a very important part of the flask as upon
them depends the matching of the two halves of the mold. A
wedge-shaped piece, CC, is nailed to each end of the cope, and the
lower pieces, DD, are then nailed on the drag so that they just
touch C when the flask is closed. The two halves of the flask will
then occupy exactly the same relative position whenever they are
put together.

After the flask is done make two boards as shown at K, Fig. 1, a
little larger than the outside of the flask. A couple of cleats
nailed to each board will make it easier to pick up the mold when
it is on the floor.

A cast-iron glue-pot makes a very good crucible for melting the
metal, which can be either aluminum, white metal, zinc or any
other metal having a low melting-point. This completes the
equipment with the exception of one or two simple devices which
will now be described.

** II - How to Make a Mold [96]

Having finished making the flask and other equipment, as
described, everything will be ready for the operation of molding.
It would be well for those who have never had any experience in
this line to visit a small brass foundry, where they can watch the
molders at work, as it is much easier to learn by observation; but
they must not expect to make a good mold at the first trial. The
first attempt usually results in the sand dropping out of the cope
when it is being lifted from the drag, either because of
insufficient ramming around the edges or because the sand is too

A good way to tell when the sand is moist enough is to squeeze it
in the hand. If it forms into a cake and shows all the
finger-marks, it has a sufficient amount of moisture, but if it
crumbles or fails to cake it is too dry. An ordinary watering-pot
will be found useful in moistening the sand, but care should be
taken not to get it too wet, or the hot metal coming in contact
with it when the mold is poured will cause such rapid evaporation
that the mold will "boil" and make a poor casting. A little
practice in this operation will soon enable the molder to
determine the correct amount of moisture.

When molding with sand for the first time it will be necessary to
screen it all before using it, in order to remove the lumps, and
if water is added, the sand should be thoroughly shoveled until
the moisture is evenly distributed. The sand is then ready for

The operation of making a mold is as follows: The lower half of
the flask, or "drag," and the pattern to be molded are both placed
on the cover board as shown at A. A quantity of sand sufficient to
completely cover the pattern is then sifted into the drag, which
is then filled level with the top with unscreened sand. This is
rammed down slightly with the rammer, and then more sand is added

[Illustration: Fig,. 3-Making a Mold]

it becomes heaped up as shown at B. It is then rammed again as

It is impossible to describe just how hard a mold should be
rammed, but by observing the results the beginner can tell when a
mold is too hard or too soft, and thus judge for himself. If the
sand falls out of the flask when lifting the cope, or if it opens
up or spreads after it is poured, it shows that the mold has been
rammed too little, and if the surface of the sand next to the
pattern is cracked it shows that the mold has been rammed too
hard. It will be found that the edges of the mold can stand a
little more ramming than the middle. In finishing the ramming,
pound evenly all over the surface with the blunt end of the

After ramming, scrape off the surplus sand with a straight-edged
stick, as shown at C, and scatter about 1/16 in. of loose sand
over the surface for a good bearing. Place another cover board on
top, as shown at D, and by grasping with both hands, as shown,
turn the drag other side up. Remove the upper cover board and
place the upper half of the flask, or "cope," in position, as
shown at E.

In order to prevent the two layers of sand sticking together, the
surface of the sand at E should be covered with coal-dust. This is
done by shaking the coal-dust bag over the flask, after which the
dust on the pattern may be removed by blowing. The cope is then
filled with sand and rammed in exactly the same manner as in the
case of the drag.

After the ramming is done a number of vent holes are made, as
shown at F, from the surface of the mold to the pattern, in order
to allow the escape of air and steam when the mold is being
poured. These vent holes may be made by pushing a wire about the
size of a knitting-needle down through the sand until it touches
the pattern. The "sprue," or pouring-hole, is next cut, by means
of the sprue-cutter shown at the right, which consists of a piece
of thin brass or steel tubing about 3/4 in. in diameter.

Now comes the critical part of the molding operation--that of
lifting the cope from the drag. It is here that the amateur often
becomes discouraged, as the sand is liable to fall out of the cope
and spoil the mold; but with a little practice and patience the
molder can lift the cope every time without breaking it, as shown
at G.

The next operation is that of cutting the gate, which carries the
molten metal from the sprue to the opening left by the pattern.
This is done with a spoon, a channel being cut about 3/4 in. wide
and about 1/4 in. deep. The pattern is then drawn from the mold,
as shown at H, by driving a sharp pointed steel rod into the
pattern and lifting it from the sand. When a metal pattern is used
a thread rod is used, which is screwed into a tapped hole in the
pattern. Before drawing it is well to tap the drawing-rod lightly
with another and larger rod, striking it in all directions and
thus loosening the sand slightly from the pattern. Some molders
tap the pattern gently when withdrawing, as shown at H, in order
to loosen any sand which has a tendency to stick.

After drawing the pattern, place the cope back on the drag, as
shown at J. Place a brick or other flat, heavy object on top of
the mold above the pattern, to prevent the pressure of the melted
metal separating the two halves of the mold, and then pour.

** III- Melting and Pouring [98]

Having prepared one or more molds, the next operation is that of
melting and pouring. An ordinary cast-iron glue-pot makes a good
crucible and can be easily handled by a pair of tongs, made out of
steel rod, as shown in the sketch. In order to hold the tongs
together a small link can be slipped on over the handle, thus
holding the crucible securely.

A second piece of steel rod bent in the form of a hook at the end
is very useful for supporting the weight of the crucible and
prevents spilling the molten metal should the tongs slip off the
crucible. The hook is also useful for removing the crucible from
the fire, which should be done soon after the metal is entirely
melted, in order to prevent overheating. The metal should be
poured into the mold in a small stream, to give the air a chance
to escape, and should not be poured directly into the center of
the opening, as the metal will then strike the bottom hard enough
to loosen the sand, thus making a dirty casting.

[Illustration: Fig. 4 -Pouring the Metal]

If, after being poured, the mold sputters and emits large volumes
of steam, it shows that the sand is too wet, and the castings in
such cases will probably be imperfect and full of holes.

A mold made in the manner previously described may be poured with
any desired metal, but a metal which is easily melted will give
the least trouble. One of the easiest metals to melt and one which
makes very attractive castings is pure tin. Tin melts at a
temperature slightly above the melting point of solder, and,
although somewhat expensive, the permanent brightness and
silver-like appearance of the castings is very desirable. A good
"white metal" may be made by mixing 75% tin, 15% lead, 5% zinc and
5% antimony. The object of adding antimony to an alloy is to
prevent shrinkage when cooling.

A very economical alloy is made by melting up all the old
type-metal, babbitt, battery zincs, white metal and other scrap
available, and adding a little antimony if the metal shrinks too
much in cooling. If a good furnace is available, aluminum can be
melted without any difficulty, although this metal melts at a
higher temperature than any of the metals previously mentioned.

In casting zincs for batteries a separate crucible, used only for
zinc, is very desirable, as the presence of a very small amount of
lead or other impurity will cause the batteries to polarize. A
very good way to make the binding posts is to remove the binding
posts from worn-out dry batteries and place them in the molds in
such a way that the melted zinc will flow around them.

The time required for a casting to solidify varies with the size
and shape of the casting, but unless the pattern is a very large
one about five minutes will be ample time for it to set. The
casting is then dumped out of the mold and the sand brushed off.
The gate can be removed with either a cold chisel or a hacksaw,
and the casting is then ready for finishing.

** Battery Switch [99]

In cases where batteries are used in series and it is desirable to
change the strength and direction of the current frequently, the
following device will be found most convenient. In my own case I
used four batteries, but any reasonable number may be used.
Referring to the figure, it will be seen that by moving the switch
A toward the left the current can be reduced from four batteries
to none, and then by moving the switch B toward the right the
current can be turned on in the opposite

[Illustration: Battey Switch]

direction to the desired strength. In the various positions of
these two switches the current from each individual cell, or from
any adjacent pair of cells, may be used in either direction.
--Contributed by Harold S. Morton, Minneapolis.

** An Optical Illusion [99]

The engraving shows a perfectly straight boxwood rule laid over a
number of turned brass rings of various sizes. Although the effect
in the illustration

[Illustration: An Optical Illusion]

is less pronounced than it was in reality, it will be noticed that
the rule appears to be bent, but sighting along the rule from one
end will show that it is perfectly straight.

The brass rings also appear distorted. The portions on one side of
the rule do not appear to be a continuation of those on the other,
but that they really are can be proved by sighting in the same
manner as before.
--Contributed by Draughtsman, Chicago.

** New Method of Lifting a Table [99]

To perform this feat effectively the little device illustrated
will be required. To make it take a sheet-iron band, A, 3/4 in.
wide and attach a strap to fasten on the forearm between the wrist
and elbow. Put a sharp needle point, B, through the sheet-iron so
that it extends 3/4 in. outward. Make one of these pieces for each
arm. In lifting the table first show the hands unprepared to the
audience and also a tight table, removing the cover to show that
the surface of the table is not prepared in any way. Then replace
the table,

[Illustration: Table Lifting Device]

rest the hands upon it and at the same time press the needle
points in the arm pieces into the wood of the table, which will be
sufficient to hold it, says a correspondent of the Sphinx. Then
walk down among the audience.

** How to Make a Paddle Boat [100]

A rowboat has several disadvantages. The operation of the oars is
both tiresome and uninteresting, and the oarsman is obliged to
travel, backward.

[Illustration: Paddle Boat]

By replacing the oars with paddles, as shown in the illustration,
the operator can see where he is going and enjoy the exercise much
better than with oars. He can easily steer the boat with his feet,
by means of a pivoted stick in the bottom of the boat, connected
by cords to the rudder.

At the blacksmith shop have a 5/8-in. shaft made, as shown at A,
Fig. 2. It will be necessary to furnish a sketch giving all the
dimensions of the shaft, which should be designed to suit the
dimensions of the boat, taking care that sufficient clearance is
allowed, so that the cranks in revolving will not strike the
operator's knees. If desired, split-wood handles may be placed on
the cranks, to prevent them from rubbing the hands.

The bearings, B, may be made of hardwood, but preferably of iron
pipe filled with melted babbitt. If babbitt is used, either
thoroughly smoke or chalk the shaft or wrap paper around it to
prevent the babbitt sticking. The pieces of pipe may be then
fastened to the boat by means of small pipe straps, such as may be
obtained at any plumber's at a very small cost.

The hubs, C, should be made of wood, drilled to fit the shaft and
mortised out to hold the paddles, D. The covers, E, may be
constructed of thin wood or galvanized iron and should be braced
by triangular boards, as shown in Fig. 1. If galvanized iron is
used, it should be exposed to the weather two or three months
before painting, or the paint will come off, spoiling its

[Illustration: Detail of Paddle Boat]

** Peculiar Properties of Ice [100]

Of all the boys who make snowballs probably few know what occurs
during the process. Under ordinary conditions water turns to ice
when the temperature falls to 32 degrees, but when in motion, or
under pressure, much lower temperatures are required to make it a
solid. In the same way, ice which is somewhat below the freezing
point can be made liquid by applying pressure, and will remain
liquid until the pressure is removed, when it will again return to
its original state. Snow, being simply finely divided ice, becomes
liquid in places when compressed by the hands, and when the
pressure is removed the liquid portions solidify and unite all the
particles in one mass. In extremely cold weather it is almost
impossible to make a snowball, because a greater amount of
pressure is then required to make the snow liquid.

This process of melting and freezing under different pressures and
a constant temperature is well illustrated by the experiment shown
in Figs. 1, 2 and 3. A block of ice, A, Fig. 1, is

[Illustration: Experiment with a Block of Ice]

supported at each end by boxes BB, and a weight, W, is hung on a
wire loop which passes around the ice as shown. The pressure of
the wire will then melt the ice and allow the wire to sink down
through the ice as shown in Fig. 2. The wire will continue to cut
its way through the ice until it passes all the way through the
piece, as shown in Fig. 3. This experiment not only illustrates
how ice melts under pressure, but also how it solidifies when the
pressure is removed, for the block will still be left in one piece
after the wire has passed through.

Another peculiar property of ice is its tendency to flow. It may
seem strange that ice should flow like water, but the glaciers of
Switzerland and other countries are literally rivers of ice. The
snow which accumulates on the mountains in vast quantities is
turned to ice as a result of the enormous pressure caused by its
own weight, and flows through the natural channels it has made in
the rock until it reaches the valley below. In flowing through
these channels it frequently passes around bends, and when two
branches come together the bodies of ice unite the same as water
would under the same conditions. The rate of flow is often very
slow; sometimes only one or two feet a day, but, no matter how
slow the motion may be, the large body of ice has to bend in

This property of ice is hard to illustrate with the substance
itself, but may be clearly shown by sealing-wax, which resembles
ice in this respect. Any attempt to bend a piece of cold
sealing-wax with the hands results in breaking it, but by placing
it between books, as shown on page 65, or supporting it in some
similar way, it will gradually change from the original shape A,
and assume the shape shown at B.

** Return-Call Bell With One Wire [101]

[Illustration: Wiring Diagram]

To use only one wire for a return call bell connect up as shown in
the diagram, using a closed circuit or gravity battery, B. The
current is flowing through both bells all the time, the same as
the coils of a telegraph sounder, but is not strong enough to ring
both connected in series. Pressing either push button, P, makes a
short circuit of that bell and rings the one at the other end of
the line.
--Contributed by Gordon T. Lane, Crafton, Pa.

** Circuit Breaker for Induction Coils [101]

Amateurs building induction coils are generally bothered by the
vibrator contacts blackening, thus giving a high resistance
contact, whenever there is any connection made at all. This
trouble may be done away with by departing from the old
single-contact vibrator and using one with self-cleaning contacts
as shown. An old bell magnet is rewound full of No. 26 double
cotton-covered wire and is mounted

[Illustration: Interrupter for Induction Coil]

upon one end of a piece of thin sheet iron 1 in. by 5 in. as per
sketch. To the other end of the strip of iron is soldered a piece
of brass 1/64 in. by 1/4, in. by 2 in., on each end of which has
been soldered a patch of platinum foil 1/4 in. square.

The whole is connected up and mounted on a baseboard as per
sketch, the contact posts being of 1/4 in. by 1/2 in. brass, bent
into shape and provided with platinum tipped thumb screws. The
advantage of this style of an interrupter is that at each stroke
there is a wiping effect at the heavy current contact which
automatically cleans off any carbon deposit.

In the wiring diagram, A is the circuit breaker; B, the induction
coil, and C, the battery.
--Contributed by A. G. Ward, Wilkinsburg, Pa.

** Spit Turned by Water Power [102]

Many of the Bulgarian peasants do their cooking in the open air
over bonfires. The illustration shows a laborsaving machine in use
which enables the cook to go away and leave meat roasting for an
hour at a time. The

[Illustration: For a Summer Camp]

illustration shows how the spit to which the meat is fastened is
constantly turned by means of a slowly moving water wheel. Some of
our readers may wish to try the scheme when camping out. The
success depends upon a slow current, for a fast-turning wheel will
burn the meat.

** A Short-Distance Wireless Telegraph [102]

The accompanying diagrams show a wireless-telegraph system that I
have used successfully for signaling a distance of 3,000 ft. The
transmitter consists of an induction coil, about the size used for
automobiles, a key or push-button for completing the circuit, and
five dry batteries. The small single-point switch is left open as
shown when sending a message, but when receiving it should be
closed in order that the electric waves from the antenna may pass
through the coherer. The coherer in this case is simply two
electric-light carbons sharpened to a wedge at one end with a

[Illustration: Wiring Diagram for Wireless Telegraph]

connecting the two, as shown. An ordinary telephone receiver is
connected in series with the coherer, as shown. To receive
messages hold the receiver to the ear and close the switch, and
answer by opening the switch and operating the key. --Contributed
by Coulson Glick, Indianapolis.

** Automatic Draft-Opener [102]

A simple apparatus that will open the draft of the furnace at any
hour desired is illustrated. The parts are: A, furnace; B, draft;
C, draft chain; D, pulleys; E, wooden supports; F, vertical lever;
G, horizontal lever; H, cord; I, alarm clock; J, weight. K shows
where and how the draft is regulated during the day, the automatic

[Illustration: Draft Regulator]

device being used to open it early in the morning. The spool on
the alarm clock is fastened to the alarm key by sawing a slit
across the top of the spool and gluing it on. When the alarm goes
off a cord is wound up on the spool and pulls the horizontal lever
up, which releases the vertical lever and allows the weight to
pull the draft open.
--Contributed by Gordon Davis, Kalamazoo, Mich.

** A Window Conservatory [103]

During the winter months, where house plants are kept in the home,
it is always a question how to arrange them so they can get the
necessary light without occupying too much room.

The sketch shows how a neat window conservatory may be made at
small cost that can be fastened on the house just covering a
window, which will provide a fine place for the plants. The frame
(Fig. 2) is made of about 2 by 2-in. material framed together as
shown in Fig. 3. This frame should be made with the three openings
of such a size that a four-paned sash, such as used for a storm
window, will fit nicely in them. If the four vertical pieces that
are shown in Fig. 2 are dressed to the right angle, then it will
be easy to put on the finishing corner boards that hold the sash.

[Illustration: Artistic Window Boxes]

The top, as well as the bottom, is constructed with two small
pieces like the rafters, on which is nailed the sheathing boards
and then the shingles on top and the finishing boards on the

** How to Make an Electroscope [103]

An electroscope for detecting electrified bodies may be made out
of a piece of note paper, a cork and a needle. Push the needle
into the cork, and cut the paper in the shape of a small arrow.
Balance the arrow on the needle

[Illustration: Simple Electroscope]

as shown in the sketch, and the instrument will then be complete.
If a piece of paper is then heated over a lamp or stove and rubbed
with a piece of cloth or a small broom, the arrow will turn when
the paper is brought near it.
--Contributed by Wm. W. Grant, Halifax, N. S., Canada.

** Miniature Electric Lighting [104]

Producing electric light by means of small bulbs that give from
one-half to six candle power, and a suitable source of power, is
something that will interest the average American boy.

These circular bulbs range from 1/4 to 2 in. in diameter, and cost
27 cents

[Illustration: FIG. 1]

each complete with base. They are commonly known as miniature
battery bulbs, since a battery is the most popular source of
power. The 1/2-cp. bulbs are usually 2-1/2 volts and take 1/4
ampere of current. It requires about three medium dry cells to
operate it. However, there is now upon the market a battery
consisting of 3 small dry cells connected in series, put up in a
neat case with 2 binding posts, which sells for 25 cents. This is
more economical than dry cells, as it gives about 4 volts and 3
amperes. It will run as large a lamp a 3-1/2 volts, 1 cp., for
some time very satisfactorily. More than one lamp can be run by
connecting the bulbs in parallel, as indicated by Fig. 1, which
shows the special battery with 3 dry cells in the case, and the 2
binding posts for connection with the bulbs. In this case it is
also advisable to connect several batteries in parallel also, so
as to increase the current, but maintain the voltage constant.
Thus the individual cells are in multiple series, i. e., multiples
of series of three. By keeping in mind the ampere output of the
battery and rating of the lamp, one can regulate the batteries as
required. It must be remembered, in this connection, that any
battery which is drawn upon for half of its output will last
approximately three times as long, as if drawn upon for its total
output. Thus, in any system of lamps, it is economical to provide
twice as many batteries as necessary. This also supplies a means
of still maintaining the candle power when the batteries are
partially exhausted, by connecting them in series. However, this
must be done with very great caution, as the lights will be burnt
out if the voltage is too high.

Persons living in the city will find an economical means of
lighting lamps by securing exhausted batteries from any garage,
where they are glad to have them taken away. A certain number of
these, after a rest, can be connected up in series, and will give
the proper voltage.

In conclusion, for battery power: Connecting batteries in series
increases the voltage, and slightly cuts down the current or
amperage, which is the same as that of one battery; while
connecting batteries in parallel increases the amperage, but holds
the voltage the same as that of one cell. Thus, if the voltage and
amperage of any cell be known, by the proper combination of these,
we can secure the required voltage and amperage to light any
miniature lamp. And it might be said that dry cells are the best
for this purpose, especially those of low internal resistance.

[Illustration: FIG.2]

For those having a good water supply there is a more economical
means of maintenance, although the first cost is greater. Fig. 2
shows the scheme. A small dynamo driven by a water motor attached
to a faucet, generates the power for the lights. The cost of the
smallest outfit of the kind is about $3 for the water motor and $4
for the dynamo. This dynamo has an output of 12 watts, and will
produce from 18 to 25 cp., according to the water pressure
obtainable. It is advisable to install the outfit in the basement,
where the water pressure is the greatest, and then lead No. 18 B &
S. double insulated wire wherever needed. The dynamo can also be
used as a motor,

[Illustration: Fig. 3]

and is wound for any voltage up to ten. The winding should
correspond to the voltage of the lamps which you desire to run.
However, if wound for 6 volts, one could run parallel series of
two 3-volt, 1-cp. lamps; making, as in Fig. 3, 11 series, or 22
lights. If wound for 10 volts, it would give 1-1/4 amperes and run
four 6-cp. lamps. Thus, it will be seen that any candle power lamp
can be operated by putting the proper number of lights in each
series, and running the series in parallel. So, to secure light by
this method, we simply turn on the water, and the water
consumption is not so great as might be imagined.

For the party who has electric light in his house there is still
an easier solution for the problem of power. If the lighting
circuit gives 110 volts he can connect eleven 10-volt lamps in
series. These will give 3 cp. each, and the whole set of 11 will
take one ampere of current, and cost about the same as a 32-cp.
lamp, or 1-1/4 cents per hour. Simply connect the miniature
circuit to an Edison plug, and insert in the nearest lamp socket.
Any number of different candle power lamps can be used providing
each lamp takes the same amount of current, and the sum of their
voltages equals the voltage of the circuit used. This arrangement
of small lights is used to produce a widely distributed, and
diffused light in a room, for display of show cases, and for
Christmas trees. Of all these sources of power the two last are
the most economical, and the latter of these two has in its favor
the small initial cost. These lamps are by no means playthings or
experiments, but are as serviceable and practical as the larger
--Contributed by Lindsay Eldridge, Chicago.

** How to Make a New Language [105]

Anyone possessing a phonograph can try a very interesting and
amusing experiment without going to any expense. Remove the belt
and replace with a longer one, which can be made of narrow braid
or a number of strands of yarn. The new belt should be long enough
to allow crossing it, thus reversing the machine. This reverses
every sound on the record and changes it to such an extent that
very few words can be recognized.

** How to Make a Cup-and-Saucer Rack [105]

The rack is made of any suitable kind of wood, and the sides, A,
are cut just alike, or from one pattern. The shelves are made in
various widths to fit the sides at the places where they are
wanted. The number of shelves can be varied and to suit the size
of the dishes. Cup hooks are placed on top and bottom shelves. It
is hung on the wall the same as a picture from the molding.
--Contributed by F. B. Emig, Santa Clara, Cal.

[Illustration: Cup-and-Saucer Rack]

Reversing a Small Motor [105]

All that is necessary for reversing the motor is a pole-changing
switch. Connect the two middle posts of the switch with each other
and the two outside posts with each other. Then connect one of the
outside posts of the switch to one brush of the motor and one
middle post to the other brush.

Connect one bar of the switch to one end of the field coil and the
other bar to one pole of the battery, and connect the other pole
of the battery to the other field coil. To reverse the motor,
simply change the switch.

[Illustration: Reverse for a Small Motor]

Referring to the illustration, the letters indicate as follows:
FF, field of motor; BB, brushes of motor; AA, bars of
pole-changing switch; DD, center points of switch; CC, outside
points of switch.
--Contributed by Leonard E. Parker, Plymouth, Ind.

** To Drive Away Dogs [106]

The dogs in my neighborhood used to come around picking up scraps.
After I connected up my induction coil, as shown in the sketch, we
were not bothered with them. A indicates the ground; B, switch;
and C, a bait of meat, or a tempting bone.

[Illustration: Shocking-Machine]

--Contributed by Geo. W. Fry, 903 Vine St., San Jose, Cal.

** An Automatic Lock [106]

The illustration shows an automatic lock operated by electricity,
one cell being sufficient. When the circuit is broken a weight, A,
attached to the end of the armature B, tends to push the other end
of the armature into the screw eye or hook C, which is in the
door, thus locking the door.

To unlock the door, merely push the button E, The magnet then
draws the armature out of the screw eye and the door is unlocked.
The dotted line at D shows the position of the armature when the
circuit is complete and the door unlocked. The weight must be in
proportion to the strength of the magnet. If it is not, the door
will not

[Illustration: Automatic Electric Lock for Doors]

lock, or would remain locked. The button can be hidden, as it is
the key to the lock.
--Contributed by Claude B. Melchior, Hutchinson, Minn.

** Experiment with Two-Foot Rule and Hammer [106]

An example of unstable equilibrium is shown in the accompanying
sketch. All that is needed is a 2-foot rule, a hammer, a piece of
string, and a table or bench. The experiment works best

[Illustration: An Experiment in Equilibrium]

with a hammer having a light handle and a very heavy head.

Tie the ends of the string together, forming a loop, and pass this
around the hammer handle and rule. Then place the apparatus on the
edge of the table, where it will remain suspended as shown.
--Contributed by Geo. P. Schmidt, Culebra, Porto Rico, W. I.

** Simple Current Reverser [107]

On a block of hardwood draw a square (Fig. 1) and drill a hole in
each corner of the square. Fill these holes with mercury and
connect them to four binding posts (Fig. 1).

On another block of wood fasten two wires, as shown in Fig. 2, so
that their ends can be placed in the holes in the first block.
Then connect up with the

[Illustration: Details of Reverser]

motor and battery as in Fig. 3. When the block is placed on with
the big arrow A pointing in the direction indicated in Fig. 3, the
current flows with the small arrows. To reverse turn through an
angle of 90 degrees (Fig. 4). -- Contributed by F. Crawford Curry,
Brockville, Ontario, Canada.

** Alarm Clock to Pull up Furnace Draft [107]

A stout cord, A, is attached to the draft B of the furnace, run
through a pulley, C, in the ceiling and has a window weight, D,
attached at the other end. A small stick is put through a loop in
the cord at about the level of the table top on which the alarm
clock F stands. The other end of stick E is placed under the key G
of the alarm clock. When the alarm rings in the early morning, the
key turns, the stick

[Illustration: Automatic Time Draft-Opener]

falls away, releasing the weight, which pulls the draft open.
--Contributed by Edward Whitney, 18 Gorham St., Madison, Wis.

** How to Transmit Phonograph Music to a Distance [107]

An interesting experiment, and one calculated to mystify anyone
not in the secret, is to transmit the music or speech from a
phonograph to another part of the house or even a greater
distance. For an outdoor summer party the music can be made to
come from a bush, or tree, or from a bed of flowers. The apparatus
is not difficult to construct.

The cut shows the arrangement. Procure a long-distance telephone
transmitter, D, including the mouthpiece, and fasten it to the
reproducer of the phonograph. Also a watch case

[Illustration: The Long-Distance Phonograph]

receiver, R, which fasten to the horn. These parts may be
purchased from any electrical-supply house. Connect two wires to
the transmitter, running one direct to the receiver, and the other
to the battery, thence to a switch, S, and then to the receiver.
The more batteries used the louder will be the sound produced by
the horn, but avoid using too much battery or the receiver is apt
to heat.
--Contributed by Wm. J. Farley, Jr., Camden, N. J.

** How to Make a Telescope [108]

With a telescope like the one here described, made with his own
hands, a farmer boy not many years ago discovered a comet which
had escaped the watchful eyes of many astronomers.

First, get two pieces of plate glass, 6 in. square and 1 in.
thick, and break the corners off to make them round, grinding the
rough edges on a grindstone. Use a barrel to work on, and

[Illustration: Homemade Telescope]

fasten one glass on the top of it in the center by driving three
small nails at the sides to hold it in place. Fasten, with pitch,
a round 4-in. block of wood in the center on one side of the other
glass to serve as a handle.

Use wet grain emery for coarse grinding. Take a pinch and spread
it evenly on the glass which is on the barrel, then take the glass
with the handle and move it back and forth across the lower glass,
while walking around the barrel; also rotate the glass, which is
necessary to make it grind evenly. The upper glass or speculum
always becomes concave, and the under glass or tool convex.

Work with straight strokes 5 or 6 in. in length; after working 5
hours hold the speculum in the sunshine and throw the rays of the
sun onto a paper; where the rays come to a point gives the focal
length. If the glass is not ground enough to bring the rays to a
point within 5 ft., the coarse grinding must be continued, unless
a longer focal length is wanted.

Have ready six large dishes, then take 2 lb. flour emery and mix
in 12 qt. of water; immediately turn the water into a clean dish
and let settle 30 seconds; then turn it into another dish and let
settle 2 minutes, then 8 minutes, 30 minutes and 90 minutes, being
careful not to turn off the coarser emery which has settled. When
dry, turn the emery from the 5 jars into 5 separate bottles, and
label. Then take a little of the coarsest powder, wetting it to
the consistency of cream, and spread on the glass, work as before
(using short straight strokes 1-1/2 or 2 in.) until the holes in
the glass left by the grain emery are ground out; next use the
finer grades until the pits left by each coarser grade are ground
out. When the two last grades are used shorten the strokes to less
than 2 in. When done the glass should be semi-transparent, and is
ready for polishing.

When polishing the speculum, paste a strip of paper 1-1/3 in. wide
around the convex glass or tool, melt 1 lb. of pitch and turn on
to it and press with the wet speculum. Mold the pitch while hot
into squares of 1 in., with 1/4-in. spaces, as in Fig. 1. Then
warm and press again with the speculum, being careful to have all
the squares touch the speculum, or it will not polish evenly. Trim
the paper from the edge with a sharp knife, and paint the squares
separately with jeweler's rouge, wet till soft like paint. Use a
binger to spread it on with. Work the speculum over the tool the
same as when grinding, using straight strokes 2 in. or less.

When the glass is polished enough to reflect some light, it should
be tested with the knife-edge test. In a dark room, set the
speculum against the wall, and a large lamp, L, Fig. 2, twice the
focal length away. Place a large sheet of pasteboard, A, Fig. 2,
with a small needle hole opposite the blaze, by the side of the
lamp, so the light

[Illustration: Detail of Telescope Construction]

from the blaze will shine onto the glass. Place the speculum S,
Fig. 2, so the rays from the needle hole will be thrown to the
left side of the lamp (facing the speculum), with the knife
mounted in a block of wood and edgeways to the lamp, as in K, Fig.
2. The knife should not be more than 6 in. from the lamp. Now move
the knife across the rays from left to right, and look at the
speculum with the eye on the right side of the blade. When the
focus is found, if the speculum is ground and polished evenly it
will darken evenly over the surface as the knife shuts off the
light from the needle hole. If not, the speculum will show some
dark rings, or hills. If the glass seems to have a deep hollow in
the center, shorter strokes should be used in polishing; if a hill
in the center, longer strokes. The polishing and testing done, the
speculum is ready to be silvered. Two glass or earthenware dishes,
large enough to hold the speculum and 2 in. deep, must be
procured. With pitch, cement a strip of board 8 in. long to the
back of the speculum, and lay the speculum face down in one of the
dishes; fill the dish with distilled water, and clean the face of
the speculum with nitric acid, until the water will stick to it in
an unbroken film.

The recipe for silvering the speculum is:

Solution A:
Distilled water.............................4 oz.
Silver nitrate............................100 gr.

Solution B:
Distilled water.............................4 oz.
Caustic stick potash (pure by alcohol)....100 gr.

Solution C:
Aqua Ammonia.

Solution D:
Sugar loaf................................840 gr.
Nitric acid................................39 gr.
Alcohol (Pure).............................25 gr.

Mix solution D and make up to 25 fluid oz. with distilled water,
pour into a bottle and carefully put away in a safe place for
future use, as it works better when old:

Now take solution A and set aside in a small bottle one-tenth of
it, and pour the rest into the empty dish; add the ammonia
solution drop by drop; a dark brown precipitate will form and
subside; stop adding ammonia solution as soon as the bath clears.
Then add solution B, then ammonia until bath is clear. Now add
enough of the solution A, that was set aside, to bring the bath to
a warm saffron color without destroying its transparency. Then add
1 oz. of solution D and stir until bath grows dark. Place the
speculum, face down, in the bath and leave until the silver rises,
then raise the speculum and rinse with distilled water. The small
flat mirror may be silvered the same way. When dry, the silver
film may be polished with a piece of chamois skin, touched with
rouge, the polishing being accomplished by means of a light spiral

Fig. 3 shows the position of the glasses in the tube, also how the
rays R from a star are thrown to the eyepiece E in the side of the
tube. Make the tube I of sheet iron, cover with paper and cloth,
then paint to make a non-conductor of heat or cold. Make the
mounting of good seasoned lumber.

Thus an excellent 6-in. telescope can be made at home, with an
outlay of only a few dollars. My telescope is 64 in. long and cost
me just $15, but I used all my spare time in one winter in making
it. I first began studying the heavens through a spyglass, but an
instrument such as I desired would cost $200--more than I could
afford. Then I made the one described, with which I discovered a
new comet not before observed by astronomers.- John E. Mellish.

** How to Make "Freak" Photographs [110]

The "freak" pictures of well-known people which were used by some
daily newspapers recently made everybody wonder how the distorted
photographs were made. A writer in Camera Craft gives the secret,
which proves to be easy of execution. The distortion is
accomplished by the use of prisms, as follows: Secure from an
optician or leaded-glass establishment, two glass prisms, slightly
wider than the lens mount. The flatter they are the less they will
distort. About 20. deg. is a satisfactory angle. Secure them as
shown by the sectional sketch, using strawboard and black paper.
Then make a ring to fit over the lens mount and connect it with
the prisms in such a way as to exclude all light from the camera
except that which passes through the face of the prisms. The inner
surface of this hood must be

[Illustration: Arrangement of Prisms]

dull black. The paper which comes around plates answers nicely. If
the ring which slips over the lens mount is lined with black
velvet, it will exclude all light and hold firmly to the mount,
Place over lens, stop down well after focusing, and proceed as for
any picture.

** Another Electric Lock [110]

The details of the construction of an electrically operated lock
are shown in the illustration. When the door is closed and the
bolt A pushed into position,

[Illustration: Simple Electric Lock]

it automatically locks. To unlock, push the button D, which act
will cause the electromagnet to raise the latch C, when the bolt
may be drawn and the door opened.
--Contributed by A. D. Zimmerman, Boody, Ill.

** How to Mix Plaster of Paris [110]

For the mixing of plaster of Paris for any purpose, add the
plaster gradually to the water, instead of the contrary, says the
Master Painter. Do not stir it, just sprinkle it in until you have
a creamy mass without lumps. Equal parts of plaster and water is
approximately the correct proportion. The addition of a little
vinegar or glue water will retard the setting of the plaster, but
will not preserve its hardening. Marshmallow powder also retards
the setting. In this way the plaster may be handled a long time
without getting hard. If you wish the plaster to set extra hard,
then add a little sulphate of potash, or powdered alum.

** Enlarging with a Hand Camera [111]

Everyone who owns a hand camera has some pictures he would like
enlarged. It is not necessary to have a large camera to do this,
as the process is exceedingly simple to make large pictures from
small negatives with the same hand camera.

A room from which all light may be excluded and a window through
which the light can enter without obstruction from trees or nearby
buildings, with a shelf to hold the camera and a table with an
upright drawing-board attached, complete the arrangement. The back
is taken out of the camera and fitted close against the back of
the shelf, which must be provided with a hole the same size and
shape as the opening in the back of the camera. The negative used
to make the enlarged print is placed in the shelf at A, Fig. 1.
The rays of the clear, unobstructed light strike the mirror, B,
and reflect through the negative, A, through the lens of the
camera and on the board, as shown in Fig. 2. The window must be
darkened all around the shelf.

After placing the negative and focusing the lens for a clear image
on the board, the shutter is set and a bromide paper is placed on
the board. The paper is exposed, developed and fixed by the
directions that are enclosed in the package of bromide papers.

[Illustration: Making Large Pictures with a Small Camera]

** Positioning A Hanging Lamp [111]

Don't pull a lamp hung by flexible cord to one side with a wire
and then fasten to a gas pipe. I have seen a wire become red hot
in this manner. If the lamp hung by a cord must be pulled over,
use a string.

A Curious Compressed Air Phenomenon [111]

Push a pin through an ordinary business card and place the card
against one end of a spool with the pin inside the bore, as shown
in the sketch. Then blow through the spool, and it will be found
that the card will not be blown away, but will remain suspended
without any visible support. This phenomenon is explained by the
fact that the air radiates from the center at a velocity which is
nearly constant, thereby producing a partial vacuum between the
spool and the card. Can the reader devise a practical application
of this contrivance?

[Illustration: Experiment with Spool and Card]

** Simple Switch for Reversing a Current [111]

Take two strips of copper or brass and fasten them together by
means of gutta-percha (Fig. 1); also provide them with a handle.
Saw out a rectangular block about one and one-half times as long
as the brass strips and fasten to it at each end two forked pieces
of copper or brass, as in Fig. 2. Fasten on the switch lever, as
at A and B, Fig. 2, so that it can rotate about these points.
Connect the wires as shown in Fig. 3. To reverse, throw

[Illustration: Simple Current-Reversing Switch]

the lever from one end of the block to the other.
--Contributed by R. L. Thomas, San Marcos, Tex.

** Novel Mousetrap [112]

A piece of an old bicycle tire and a glass fruit jar are the only
materials required for making this trap. Push one end of the tire
into the hole, making sure that there is a space left at the end
so that the mice can get in. Then

[Illustration: A Baitless Trap]

bend the other end down into a fruit jar or other glass jar. Bait
may be placed in the jar if desired, although this is not
--Contributed by Geo. Go McVicker, North Bend, Neb.

** Polishing Nickel [112]

A brilliant polish may be given to tarnished nickel by immersing
in alcohol and 2 per cent of sulphuric acid from 5 to 15 seconds.
Take out, wash in running water, rinse in alcohol, and rub dry
with linen cloth.

** Homemade Arc Light [112]

By rewinding an electric-bell magnet with No. 16 wire and
connecting it in series with two electric-light carbons, as shown
in the sketch, a small arc will be formed between the carbon
points when the current is applied. In the sketch, A is the
electric-bell magnet; B, the armature; C C, carbon sockets; D,
carbons, and E E, binding posts. When connected with 10 or 12 dry
batteries this lamp gives a fairly good light.
--Contributed by Morris L. Levy, San Antonio, Tex.

[Illustration: Arc Light]

** Lighting an Incandescent Lamp with an Induction Coil [112]

An incandescent lamp of low candlepower may be illuminated by
connecting to an induction coil in the manner shown in the sketch.
One wire is connected to the metal cap of the lamp and the other
wire is fastened to the glass tip. If the apparatus is then placed
in the dark and the current turned on, a peculiar phosphorescent
glow will fill the whole interior of the lamp. The induction coil
used for this purpose should give a spark about 1/2 in. long or
--Contributed by Joseph B. Bell, Brooklyn.

[Illustration: Geissler Tube]

How to Make a Jump-Spark Coil [113]

The induction coil is probably the most popular piece of apparatus
in the electrical laboratory, and particularly is it popular
because of its use in experimental wireless telegraphy. Ten years
ago wireless telegraphy was a dream of scientists; today it is the
plaything of school-boys and thousands of grown-up boys as well.

Divested of nearly all technical phrases, an induction coil may be
briefly described as a step-up transformer of small capacity. It
comprises a core consisting of a cylindrical bundle of soft-iron
wires cut to proper length. By means of two or more layers of No.
14 or No. 16 magnet wire, wound evenly about this core, the bundle
becomes magnetized when the wire terminals are connected to a
source of electricity.

Should we now slip over this electromagnet a paper tube upon which
has been wound with regularity a great and continuous length of
No. 36 magnet wire, it will be found that the lines of force
emanating from the energized core penetrate the new coil-winding
almost as though it were but a part of the surrounding air itself,
and when the battery current is broken rapidly a second electrical
current is said to be induced into the second coil or secondary.

All or any of the parts of an induction coil may be purchased
ready-made, and the first thing to do is to decide which of the
parts the amateur mechanic can make and which would be better to
buy ready-made. If the builder has had no experience in
coilwinding it would probably pay to purchase the secondary coil
ready-wound, as the operation of winding a mile or more of fine
wire is very difficult and tedious, and the results are often
unsatisfactory. In ordering the secondary it is always necessary
to specify the length of spark desired.

The following method of completing a 1-in. coil illustrates the
general details of the work. The same methods and circuits apply
to small and larger coils. The ready-made secondary is in solid
cylindrical form, about 6 in. long and 2-5/8 in. diameter, with a

[Illustration: Jump-Spark Coil]

through the winding 1-1/4 in. in diameter, as shown in Fig. 1. The
secondary will stand considerable handling without fear of injury,
and need not be set into a case until the primary is completed.
The primary is made of fine annealed No. 24 iron wire cut 7 in. or
8 in. in length, as the maker prefers, and bundled to a diameter
of 7/8 in. The wires may be straightened by rolling two or three
at a time between two pieces of hard wood. If the amateur has
difficulty in procuring this wire, the entire core may be
purchased ready-made.

After the core wires are bundled, the core is wrapped with one or
two layers of manila paper. The straighter the wire the more iron
will enter into the construction of the core, which is desirable.
Beginning half an inch from one end, No. 16 cotton-covered magnet
wire is wound from one end to the other evenly and then returned,
making two layers, and the terminals tied down to the core with
twine. Core and primary are then immersed in boiling paraffine wax
to which a small quantity of resin and beeswax has been added.
This same wax may be used later in sealing the completed coil into
a box. Over this primary is now wrapped one layer of okonite tape,
or same thickness of heavily shellacked muslin. This completed
primary will now allow of slipping into the hole in the secondary.

Should the secondary have been purchased without a case, a wooden
box of mahogany or oak is made, large enough to contain the
secondary and with an inch to spare all around, with room also for
a small condenser; but if it is not convenient to do this work, a
box like that shown in Fig. 2 may be purchased at a small cost. A
7/8-in. hole is bored in the center of one end, through which the
primary core projects 1/8 in. This core is to be used to attract
magnetically the iron head of a vibrating interrupter, which is an
important factor of the coil. This interrupter is shaped as in
Fig. 4, and is fastened to the box in such a way that the vibrator
hammer plays in front of the core and also that soldered
connections may be made inside the box with the screws used in
affixing the vibrator parts to the box. The condenser is made of
four strips of thin paper, 2 yd. long and 5 in. wide, and a
sufficient quantity of tinfoil. When cut and laid in one
continuous length, each piece of tin-foil must overlap the
adjoining piece a half inch, so as to form a continuous electrical
circuit. In shaping the condenser, one piece of the paper is laid
down, then the strip of tin-foil, then two strips of paper and
another layer of foil, and finally the fourth strip of paper. This
makes a condenser which may be folded, beginning at one end and
bending about 6 in. at a time. The condenser is next wrapped
securely with bands of paper or tape, and boiled in pure paraffine
wax for one hour, after which it is pressed under considerable
weight until firm and hard. One of the sheets of tin-foil is to
form one pole of the condenser, and the other sheet, which is
insulated from the first, forms the other pole or terminal. (This
condenser material is purchasable in long strips, ready for

The wiring diagram, Fig. 3, shows how the connections are made.
This method of connecting is suitable for all coils up to 1-1/2
in. spark, but for larger coil better results will be obtained by
using an independent type of interrupter, in which a separate
magnet is used to interrupt the circuit. Besides the magnetic
vibrators there are several other types, such as the mercury
dash-pot and rotary-commutator types, but these will become better
known to the amateur as he proceeds in his work and becomes more
experienced in coil operation.

** Combined Door Bell and Electric Alarm [114]

This device consists of a battery and bell connection to an alarm
clock which also acts as a door bell, the whole being mounted on a
board 18 in. long and 12 in. wide. Referring to the sketch
accompanying this article, the letters indicate as follows: A,
bell; B, battery ; C, switch; D, V-shaped copper strip; E, copper
lever with 1-in. flange turned on one side, whole length, 4 in.;
F, spring to throw lever E down in V-shaped piece to make
connection; G, lever to hold out E when device is used as a door
bell; lines H, go, one from bell, A, and one from battery, B, to
the door; I, shelf for clock.

See that the ring in the alarm key of the clock works easily, so
that when it is square across the clock it will drop down. Fasten
a piece of copper about

[Illustration: Wiring Disgram]

1 in. long to key, then wind the alarm just enough so that the key
stands straight up and down. Place the clock on the shelf and the
key under the flange of lever E. Pull lever G down out of the way
and close the lever on the switch. The alarm key will turn and
drop down, letting lever E drop into the V-shaped piece D and make

For the door-bell connection close lever on switch C, and put G up
so that D and E do not come in contact. If anyone is ill and you
do not want the bell to ring, open switch C.

The wiring for this device may all be on the back of the board.
The switch and levers are fastened with small screw bolts, which
allows wiring at the back. Saw two spools in half and fasten the
halves to the four corners of the board at the back, and the
apparatus may be put up where one likes.

**v To Build a Small Brass Furnace [115]

Bend a piece of stout sheet iron 23 in. by 12 in. round so that
the inside

[Illustration: Furnace]

diameter is 7 in., and then rivet the seam. Fit in a round piece
of sheet iron for the bottom. Make a hole about the size of a
shilling in the side, 2 in. from the bottom. This is for blowing.

Line the furnace, bottom and sides with fire-clay to a depth of
1/2 in. Use charcoal to burn and an ordinary bellows for blowing,
says the Model Engineer, London. The best blast is obtained by
holding the nozzle of the bellows about an inch from the hole,
instead of close to it.

** Avoid Paper Lamp Shades [115]

Don't wrap paper around a lamp for a shade. You might go away and
forget it and a fire might be started from the heat. Use a glass
or metal shade. That is what they are for.

** Why Gravity Batteries Fail to Work [115]

Many amateur electricians and some professionals have had
considerable trouble with gravity batteries. They

[Illustration: Setting Up a Gravity Battery]

follow directions carefully and then fail to get good results.
The usual trouble is not with the battery itself, but with the
circuit. A gravity battery is suitable only for a circuit which is
normally closed. It is therefore undesirable for electric bells,
induction coils and all other open-circuit apparatus. The circuit
should also have a high resistance. This makes it impractical for
running fan motors, as the motor would have to be wound with fine
wire and it would then require a large number of batteries to give
a sufficiently high voltage.

To set up a gravity battery: Use about 3-1/2 lb. of blue stone, or
enough to cover the copper element 1 in. Pour in water sufficient
to cover the zinc 1/2 in. Short-circuit for three hours, and the
battery is ready for use. If desired for use immediately, do not
short-circuit, but add 5 or 6 oz. of zinc sulphate.

Keep the dividing line between the blue and white liquids about
1/2 in. below the bottom of the zinc. If too low, siphon off some
of the white liquid and add the same amount of water, but do not
agitate or mix the two solutions. This type of battery will give
about 0.9 of a volt, and should be used on a circuit of about 100

** A Skidoo-Skidee Trick [116]

In a recent issue or Popular Mechanics an article on "The Turning
Card Puzzle" was described and illustrated. Outside of the
scientific side involved, herein I describe a much better trick.
About the time when the expression "skidoo" first began to be used
I Invented the following trick and

[Illustration: How to Cut the Notches]

called it "Skidoo" and "Skidee," which created much merriment.
Unless the trick is thoroughly understood, for some it will turn
one way, for others the opposite way, while for others it will not
revolve at all. One person whom I now recall became red in the
face by shouting skidoo and skidee at it, but the thing would not
move at all, and he finally from vexation threw the trick into the
fire and a new one had to be made. Very few can make it turn both
ways at will, and therein is the trick.

Take a piece of hardwood 3/8 in. square and about 9 in. long. On
one of the edges cut a series of notches as indicated in Fig. 1.
Then slightly taper the end marked B until it is nicely rounded as
shown in Fig. 2. Next make an arm of a two-arm windmill such as
boys make. Make a hole through the center or this one arm. Enlarge
the hole slightly, enough to allow a common pin to hold the arm to
the end B and not interfere with the revolving arm. Two or three
of these arms may have to be made before one is secured that is of
the exact proportions to catch the vibrations right.

To operate the trick, grip the stick firmly in one hand, and with
the forward and backward motion of the other allow the first
finger to slide along the top edge, the second finger along the
side, and the thumb nail will then vibrate along the notches, thus
making the arm revolve in one direction. To make the arm revolve
in the opposite direction--keep the hand moving all the time, so
the observer will not detect the change which the hand makes
--allow the first finger to slide along the top, as in the other
movement, the thumb and second finger changing places: e. g., In
the first movement you scratch the notches with the thumb nail
while the hand is going from the body, and in the second movement
you scratch the notches with the nail of the second finger when
the hand is coming toward the body, thus producing two different
vibrations. In order to make it work perfectly (?) you must or
course say "skidoo" when you begin the first movement, and then,
no matter how fast the little arm is revolving when changed to the
second movement you must say "skidee" and the arm will immediately
stop and begin revolving in the opposite direction. By using the
magic words the little arm will obey your commands instantly and
your audience will be mystified. If any or your audience presume
to dispute, or think they can do the same let them try it. You
will no doubt be accused of blowing or drawing in your breath, and
many other things in order to make the arm operate. At least it is
amusing. Try it and see.
--Contributed by Charles Clement Bradley Toledo, Ohio.

** Effects of Radium [116]

Radium acts upon the chemical constituents of glass, porcelain and
paper, imparting to them a violet tinge; changes white phosphorus
to yellow, oxygen to ozone, affects photograph plates and produces
many other curious chemical changes.

** Naval Speed Record [116]

On its official trial trip the British torpedo boat destroyer
"Mohawk" attained the record speed of a little over 39 miles an

** How to Enlarge from Life in the Camera [117]

Usually the amateur photographer gets to a point in his work where
the miscellaneous taking of everything in sight is somewhat
unsatisfying: There are many special fields he may enter, and one
of them is photomicrography. It is usually understood that this
branch of photography means an expensive apparatus. If the worker
is not after too high a magnification, however, there is a very
simple and effective means of making photomicrographs which
requires no additional apparatus that cannot be easily and quickly
constructed at home.

Reproduced with this article is a photograph of dandelion seeds --
a magnification of nine diameters or eighty-one times. The
apparatus which produced this photograph consisted of a camera of
fairly long draw, a means for holding it vertical, a short-focus
lens, and, if possible, but not essential, a means for focusing
that lens in a minute manner. On top of the tripod is the folding
arrangement, which is easily constructed at home with two hinged
boards, an old tripod screw, an old bed plate from a camera for
the screw to fit in, and two sliding brass pieces with sets crews
that may be purchased from any hardware store under the name of
desk sliding braces. To the front board is attached a box,
carrying the lens and the bed of the sliding object carrier, which
can be moved forward and back by the rack and pinion, that also
can be obtained from hardware stores. If the bed for the object
carrier be attached to the bed of the camera instead of to the
front board, the object carrier need have no independent movement
of its own, focusing being done by the front and

[Illustration: Enlargement with a Camera]

back focus of the camera; but this is less satisfactory,
particularly when accurate dimensions are to be determined, says
the Photographic Times. This outfit need not be confined to seeds
alone, but small flowers, earth, chemicals, insects, and the
thousand and one little things of daily life--all make beautiful
subjects for enlarged photographs. These cannot be made by taking
an ordinary photograph and enlarging through a lantern. When a
gelatine dry plate is magnified nine diameters, the grains of
silver in the negative will be magnified also and produce a result
that will not stand

[Illustration: Magnified Nine Diameters]

close examination. Photographs made by photomicrography can be
examined like any other photographs and show no more texture than
will any print.

** Steel Pen Used in Draftsman's Ink Bottle Cork [117]

A steel pen makes an ideal substitute for a quill in the stopper
of the draftsman's ink bottle. The advantage of this substitute is
that there is always one handy to replace a broken or lost pen,
while it is not so with the quill.
--Contributed by George C. Madison, Boston, Mass.

** How to Make a Pilot Balloon [118]
By E. Goddard Jorgensen

Unusual interest is being displayed in ballooning, and as it is
fast becoming the favorite sport many persons would like to know
how to construct a miniature balloon for making experiments. The
following table will give the size, as well as the capacity and
lifting power of pilot balloons:

Diameter. Cap. in Cu. Ft Lifting Power.
5 ft. 65 4 lb.
6 ft. 113 7 lb.
7 ft. 179 11 lb.
8 ft. 268 17 1b.
9 ft. 381 24 lb.
10 ft. 523 33 lb.
11 ft. 697 44 lb.
12 ft. 905 57 lb.

The material must be cut in suitable shaped gores or segments. In
this article we shall confine ourselves to a 10-ft. balloon. If
the balloon is 10 ft. in diameter, then the circumference will be
approximately 3-1/7 times the diameter, or 31 ft. 5 in. We now
take one-half this length to make the length of the gore, which is
15 ft. 7-1/2 in. Get a piece of paper 15 ft. 7-1/2 in. long and 3
ft. wide from which to cut a pattern, Fig. 1. A line, AB, is drawn
lengthwise and exactly in the middle of the paper, and a line, CD,
is drawn at right angles to AB and in the middle of the paper
lengthways. The intersecting point of AB and CD is used for a
center to ascribe a circle whose diameter is the same as the width
of the paper, or 3 ft. Divide one-quarter of the circle

[Illustration: Pattern for Cutting the Segments]

into 10 equal parts and also divide one-half of the line AB in 10
equal parts. Perpendicular lines are drawn parallel with the line
CD intersecting the division points made on the one-half line AB.
Horizontal and parallel lines with AB are drawn intersecting the
division points made on the one-quarter circle and intersecting
the perpendicular line drawn parallel with CD. A line is now drawn
from B to E and from E to F, and so on, until all the intersecting
lines are touched and the point C is reached. This will form the
proper curve to cut the pattern. The paper is now folded on the
line AB and then on the line CD, keeping the marked part on the
outside. The pattern is now cut, cutting all four quarters at the
same time, on the curved line from B to C. When the paper is
unfolded you will have a pattern as shown in Fig. 2. This pattern
is used to mark the cloth, and after marked is cut the same shape
and size.

The cloth segments are sewed together, using a fine needle and No.
70 thread, making a double seam as shown in Fig. 3. When all seams
are completed you will have a bag the shape shown in Fig. 4. A
small portion of one end or a seam must be left open for
inflating. A small tube made from the cloth and sewed into one end
will make a better place for inflating and to tie up tightly.

It is now necessary to varnish the bag in order to make it retain
the gas. Procure 1 gal. of the very best heavy body, boiled
linseed oil and immerse the bag in it. The surplus oil is squeezed
out by running the bag through an ordinary clothes wringer several
times. The bag is now placed in the sun for a thorough drying. Put
the remaining oil in a kettle with 1/8 lb. of beeswax and boil
well together. This solution is afterward diluted with turpentine
so it will work well. When the bag is dry apply this mixture by
rubbing it on the bag with a piece of flannel. Repeat this
operation four times,

[Illustration: Sewing Segments Together]

being sure of a thorough drying in the sun each time. For indoor
coating and drying use a small amount of plumbic oxide. This will
dry rapidly in the shade and will not make the oil hard.

Fill the bag with air by using a pair of bellows and leave it over
night. This test will show if the bag is airtight. If it is not
tight then the bag needs another rubbing. The next operation is to
fill the bag with gas.

Hydrogen gas is made from iron and sulphuric acid. The amounts
necessary for a 10-ft. balloon are 125 lb. of iron borings and 125
lb. of sulphuric acid. 1 lb. of iron, 1 lb. of sulphuric acid and
4 lb. of water will make 4 cu. ft. of gas in one hour. Secure two
empty barrels of about 52 gal. capacity and connect them, as shown
in Fig. 5, with 3/4-in. pipe. In the barrel, A, place the iron
borings and fill one-half full of clear water. Fill the other
barrel, B, with water 2 in. above the level of the water in barrel
A. This is to give a water pressure head against foaming when the
generator is in action. About 15 lb. of lime should be well mixed
with the water in the barrel B. All

[Illustration: FIG. 5; The Hydrogen Generator]

joints must be sealed with plaster of Paris. Pour in one-half of
the acid into the barrel, A, with the iron borings. The barrels
are kept tight while the generation is going on with the exception
of the outlet, C, to the bag. When the action is stopped in the
generator barrel, A, let the solution run out and fill again as
before with water and acid on the iron borings. The outlet, C,
should be always connected with the bag while the generator is in
action. The 3/4-in. pipe extending down into the cooling tank, B,
should not enter into the water over 8 in. When filled with gas
the balloon is ready for a flight at the will of the operator.

** How to Clean a Clock [119]

It is very simple to clean a clock, which may sound rather absurd.
For an amateur it is not always necessary to take the clock to
pieces. With a little care and patience and using some benzine, a
clean white rag, a sable brush and some oil a clock can be cleaned
and put into first-class running order. The benzine should be
clean and free from oil. You can test benzine by putting a little
on the back of the hand; if it is good it will dry off, leaving
the hand quite clean, but if any grease remains on the hand, it is
not fit to use.

The oil should be of the very best that can be procured. Vegetable
oils should never be used. Clock oil can be procured from your
druggist or jeweler.

All loose dirt should be removed from the works by blowing with
bellows, or a fan, or dusting with a dry brush; in the latter case
great care should be exercised not to injure any of the parts. Dip
the brush in the benzine and clean the spindles and spindle holes,
and the teeth of the escapement wheel. After washing a part, wipe
the brush on the rag and rinse in the benzine; this should be
repeated frequently, until no more dirt is seen.

When the clock has dried, oil the spindle holes carefully; this
may be done with a toothpick or a sliver of woodcut to a fine
point. Oil the tooth of the escapement wheel slightly, using a
fine brush.

** How to Make Blueprint Lantern Slides [120]

Lantern slides of a blue tone that is a pleasing variety from the
usual black may be made from spoiled or old plates which have not
been developed, by fixing, washing well and then dipping five
minutes in the following solution:

A. Green Iron ammonium citrate 150 gr.
Water 1 oz.

B. Potassium ferrocyanide 50 gr.
Water 1 oz.

Prepare the solutions separately and mix equal parts for use, at
the time of employment. Dry the plates in the dark, and keep in
the dark until used. Printing is done in the sun, and a vigorous
negative must be used, says the Moving Picture World. Exposure, 20
to 30 minutes. Wash 10 minutes in running water and dry. Brown or
purple tones may be had by sensitizing with the following solution
instead of the above:

Distilled water 1 oz.
Sliver nitrate 50 gr.
Tartaric or citric acid 1/2 oz.

Bathe the plates 5 minutes, keeping the fingers out of the
solution, to avoid blackened skin. Dry in the dark. Print to
bronzing under a strong negative; fix in hypo, toning first if

** A Substitute for a Ray Filter [120]

Not many amateur photographers possess a ray filter. A good
substitute is to use the orange glass from the ruby lamp. This can
be held in position in front of the lens with a rubber band. A
longer exposure will be necessary, but good cloud effects can be
procured in this manner.

** Electric Lamp Experiments [120]

Incandescent electric lamps can be made to glow so that they may
be seen in a dark room by rubbing the globe on clothing or with a
paper, leather or tinfoil and immediately holding near a 1/2-in.
Ruhmkorff coil which is in action but not sparking. The miniature
16 cp., 20 and 22-volt lamps will show quite brilliantly, but the
110-volt globes will not glow. When experimenting with these
globes everything should be dry. A cold, dry atmosphere will give
best results.

* * * * * * *

[Illustration: Annual Regatta, Port Melbourne, Australia]

** How to Make a Simple Wireless Telegraph [121]

An efficient wireless-telegraph receiving apparatus for distances
up to 1,000 ft. may be constructed in the following manner: Attach
a watchcase telephone receiver to a dry cell, or battery, of any
make. The negative pole, or zinc, of the cell is connected to a
ground wire. This is done by attaching to a gas or water pipe. The
positive pole, or carbon, of the cell is connected to the aerial
line. This aerial collector can be made in various ways, either by
using a screen wire or numerous wires

[Illustration: For Distances up to 1000 Feet]

made in an open coil and hung in the air. File a V-shaped groove
in the upper end of the carbon of the cell. Attach a small bent
copper wire in the binding post that is attached to the zinc of
the cell. In the bend of this wire and the V-shaped groove filed
into the carbon, lay a needle. This will complete the receiving
station. Use a spark coil in connection with a telegraph key for
the sending station, making a ground with one wire, and have the
other connected with another aerial line.

By connecting the telephone receiver to the cell and at the same
time having a short circuit a receiving station is made. As the
telephone offers a high resistance, part of the current will try
to take the shorter high resistance through the needle. If the
waves strike across the needle, the resistance is less, and thus
less current travels through the telephone receiver. If the wave
ceases, the resistance between the needle and the carbon is
increased, and as less current will flow the short way, it is
compelled to take the longer metallic way through the windings of
the receiver, which will cause the clickings that can be heard.

** To Preserve Putty [121]

Putty, when left exposed to the air, will soon become dry and
useless. I have kept putty in good condition for more than a year
by placing it in a glass jar and keeping it entirely covered with

** How to Make a Small Storage Battery [121]

The cell of a storage battery consists of two plates, a positive
and a negative, made of lead and placed in a dilute solution of
sulphuric acid. Large batteries made of large cells have a great
number of plates, both positive and negative, of which all
positive plates are connected to one terminal and the negative
plates to the other terminal. The storage cell, as described
below, is the right size to be charged by a few gravity cells and
is easily made.

Secure a piece of 1-3/4-in. lead pipe, 5 in. long, and cut both
ends smooth and square with the pipe. Solder a circular disk of
lead to one end, forming a cup of the pipe. As this cup must hold
the sulphuric acid it must be perfectly liquid-tight. It is also
necessary to get another lead pipe of the same length but only
3/4-in. in diameter. In this pipe should be bored as many 1/8-in.

[Illustration: Battery]

as possible, except for about 1 in. on each end. One end of this
tube is hammered together as shown at A in the sketch to make a
pocket to hold the paste. This, of course, does not need to be

A box of wood is made to hold the larger tube or cup. This box can
be square, and the corners left open around the cup can be filled
with sawdust. A support is now made from a block of wood to hold
the tube, B, in place and to keep it from touching the cup C. This
support or block, D, is cut circular with the same diameter as the
lead cup C. The lower portion of the block is cut away so it will
just fit inside of the cup to form a stopper. The center of this
block is now bored to make a hole the same size as the smaller
lead pipe. Place the lead pipe in the hole and immerse it in
smoking hot paraffine wax, and leave it until the wood has become
thoroughly saturated with the hot wax. Use care to keep the wax
from running on the lead at any place other than the end within
the wood block. Two binding-posts should be attached, one to the
positive, or tube B, and the other to the negative, or tube C, by
soldering the joint.

A paste for the positive plate is made from 1 part sulphuric acid
and 1 part water with a sufficient amount of red lead added to
make of thick dry consistency. When mixing the acid and water, be
sure to add the acid to the water and not the water to the acid.
Also remember that sulphuric acid will destroy anything that it
comes in contact with and will make a painful burn if it touches
the hands. Stir the mixture with a stick and when a good dry paste
is formed, put it into the smaller tube and ram it down until the
tube is almost filled. The paste that may have come through the
holes is scraped off and the tube set aside to dry. The large tube
or cup is filled with a diluted solution of sulphuric acid. This
solution should be about one-twelfth acid. The cell is now
complete and ready for storing the current.

The cell may be charged with three gravity cells. These are
connected in series and the positive terminal binding-post on the
storage cell is connected to the wire leading from the copper
plate in the gravity cell. The other plate is connected to the
zinc. The first charge should be run into the cell for about one
week and all subsequent charges should only take from 10 to 12

** Fitting a Plug in Different Shaped Holes [122]

A certain king offered to give the prince his liberty if he could
whittle a plug that would fit four different shaped holes, namely:
a square hole, a round one, an oblong one and a triangular one,
says the Pathfinder. A broomstick was used to make the plug and it
was whittled in the shape shown

[Illustration: Fits Four Different Shaped Holes]

in Fig. 1. The holes in the different places as shown in Fig. 2,
were fitted by this one plug.

** How to Make a Lightning Arrester [122]

Secure a piece of wood about 3-1/2 in. square that will furnish a
nice finish and round the corners and make a small rounding edge
as shown in the sketch. From a piece of brass 1/16 in. thick cut
two pieces alike, A and B, and match them together, leaving about
1/16 in. between their upper edges and fasten them to the wood
with binding-posts. The third piece of brass, C, is fitted

[Illustration: Lightning Arrester]

between the pieces A and B allowing a space of 1/16-in. all around
the edge. One binding-post and a small screw will hold the piece
of brass, C, in place on the wood. The connections are made from
the line wires to the two upper binding-posts and parallel from
the lower binding-posts to the instrument. The third binding-post
on C is connected to the ground wire. Any heavy charge from
lightning will jump the saw teeth part of the brass and is
grounded without doing harm to the instruments used. --Contributed
by Edwin Walker, Chicago, Ill.

** A Home-Made Punt [123]

A flat bottom boat is easy to make and is one of the safest boats,
as it is not readily overturned. It has the advantage of being
rowed from either end, and has plenty of good seating capacity.

This punt, as shown in Fig. 1, is built 15 ft. long, about 20 in.
deep and 4 ft. wide. The ends are cut sloping for about 20 in.
back and under. The sides are each made up from boards held
together with battens on the inside of the boat near the ends and
in the middle. One wide board should be used for the bottom piece.
Two pins are driven in the top board of each side to serve as

The bottom is covered with matched boards not over 5 in. wide.
These pieces are placed together as closely as possible, using
white lead between the joints and nailing them to the edges of the
side boards and to a keel strip that runs the length of the punt,
as shown in Fig. 2. Before nailing the boards place lamp wicking
between them and the edges of the side boards. Only galvanized
nails should be used. In order to make the punt perfectly
watertight it is best to use the driest lumber obtainable. At one
end of the punt a skag and a rudder can be attached as shown in
Fig. 3.

[Illustration: Easy to Build and Safe to Use]

** Photographers' Printing Frame Stand [123]

When using developing papers it is always bothersome to build up
books or

[Illustration: Adjustable to Any Height]

small boxes to make a place to set the printing frame in front of
the light. Details for making a small stand that is adjustable to
any desired height are shown in the sketch. In Fig. 1 is shown the
construction of the sliding holder. A piece of 1/4-in. gas pipe,
A, is cut 1 in. long and fitted with a thumbscrew, B. The piece of
pipe is soldered to the middle on the back side of a piece of
metal that is about 4 by 4-1/2 in. with its lower edge turned up
to form a small shelf as shown at C. The main part of the stand is
made by inserting a 5/16-in. rod tightly into a block of hard
maple wood that is 1 in. thick and 3-1/2 in. square (Fig 2). The
pipe that is soldered to the metal support will slide up and down
the rod and the thumbscrew can be set to hold it at the desired

** Heat and Expansion [124]

Take an electric light bulb from which the air has not been
exhausted and immerse it in water and then break off the point. As
there is a vacuum in the bulb it will quickly fill with water.
Shake the bulb gently until a part of the water is out and then
screw the bulb into a socket with the point always downward. Apply
the current and the heated air inside will soon expand and force
the water out with great rapidity. Sometimes this experiment can
be done several times by using the same bulb.
--Contributed by Curtiss Hill, Tacoma, Wash.

** Photographing a Streak of Lightning [124]

The accompanying illustration is a remarkable photograph of a
streak of lightning. Many interesting pictures of this kind can be
made during a storm at night. The camera is set in a place where
it will not get wet and left standing with the shutter open and
the plate ready for the exposure. Should a lightning streak appear
within the range of the lens it will be made on the plate, which
can be developed in the usual manner. It will require some
attention to that part of the sky within the range of the lens so
as to not make a double exposure by letting a second flash enter
the open lens.
--Contributed by Charles H. Wagner.

* * * * *

Borax may be used as a solvent for shellac gum.

* * * * *

** How to Make a Small Single-Phase Induction Motor [124]
By C. H. Bell

The following notes on a small single-phase induction motor,
without auxiliary phase, which the writer has made, may be of
interest to some of our readers, says the Model Engineer. The
problem to be solved was the construction of a motor large enough
to drive a sewing machine or very light lathe, to be supplied with
110-volt alternating current from a lighting circuit, and to
consume, if possible, no more current than a 16-cp. lamp. In
designing, it had to be borne in mind that, with the exception of
insulated wire, no special materials could be obtained.

[Illustration: Motor]

The principle of an induction motor is quite different from that
of the commutator motor. The winding of the armature, or "rotor,"
has no connection with the outside circuit, but the current is
induced in it by the action of the alternating current supplied to
the winding of the field-magnet, or "stator." Neither commutator
nor slip rings are required, and all sparking is avoided.
Unfortunately, this little machine is not self-starting, but a
slight pull on the belt just as the current is turned on is all
that is needed, and the motor rapidly gathers speed provided no
load is put on until it is in step with the alternations of the
supply. It then runs at constant speed whether given much or
little current, but stops if overloaded for more than a few

The stator has four poles and is built up of pieces of sheet iron
used for stove pipes, which runs about 35 sheets to the inch. All
the pieces are alike and cut on the lines with the dimensions as
shown in Fig. 1, with the dotted line, C, to be filed out after
they are placed together. Each layer of four is placed with the
pointed ends of the pieces alternately to the right and left so as
to break joints as shown in Fig. 2. The laminations were carefully
built up on a board into which heavy wires had been driven to keep
them in place until all were in position and the whole could be
clamped down. In the middle of the pieces 1/4-in. holes, B, were
then drilled and 1/4-in. bolts put in and tightened up, large
holes being cut through the wood to enable this to be done. The
armature tunnel was then carefully filed out and all taken apart
again so that the rough edges could be scraped off and the
laminations given a thin coat of shellac varnish on one side.
After assembling a second time, the bolts were coated with shellac
and put into place for good. Holes 5-32 in. in diameter were
drilled in the corners, A, and filled with rivets, also varnished
before they were put in. When put together they should make a
piece 2 in. thick.

This peculiar construction was adopted because proper stampings
were not available, and as every bit of sheet iron had to be cut
with a small pair of tinners' snips, it was important to have a
very simple outline for the pieces. They are not particularly
accurate as it is, and when some of them got out of their proper
order while being varnished, an awkward job occurred in the magnet
which was never entirely corrected. No doubt some energy is lost
through the large number of joints, all representing breaks in the
magnetic circuit, but as the laminations are tightly held together
and the circuit is about as compact as it could possibly be,
probably the loss is not as great as it would appear at first

The rotor is made of laminations cut from sheet iron, as shown in
Fig. 3, which were varnished lightly on one side and clamped on
the shaft between two nuts in the usual way. A very slight cut was
taken in the lathe afterwards to true the circumference. The shaft
was turned from 1/2-in. wrought iron, no steel being obtainable,
and is shown with dimensions in Fig. 4. The bearings were cast of
babbitt metal, as shown in Fig. 5, in a wooden mold and bored to
size with a twist drill in the lathe. They are fitted with
ordinary wick lubricators. Figures 6 and 7 are sections showing
the general arrangement of the machine.

The stator is wound full with No. 22 double cotton-covered copper

[Illustration: Motor]

about 2-1/2 lb. being used, and the connections are such as to
produce alternate poles--that is, the end of the first coil is
joined to the end of the second the beginning of the second to the
beginning of the third, and the end of the third to the end of the
fourth, while the beginnings of the first and fourth coils connect

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