SCIENCE FOR THE PLAY-HOUR
$A Home-Made Electrical Machine.$--To make a really first-class machine
of the modern type would require a good deal of mechanical skill, even
supposing my readers to be the happy possessors of the necessary tools
and materials; but the older type of machine--though of course not so
powerful--will probably do quite well enough for most of their purposes.
I will, therefore, describe one of the simplest forms of these
machines, such as any one, with a little care and patience, can make
for himself.
The first thing to do is to get a general idea of what you are going to
construct, which may be had from the illustration, and from the actual
machines you may sometimes see in a shop window or in a scientific
collection, like the Science Departments of the South Kensington
Museum. It is the making of the cylinder machine we are going to
work out, and, therefore, to begin with, the glass cylinder must be
procured. This can be had from a dealer in chemical apparatus and costs
only a few pence for the smaller size--about 3 inches by 6 inches. At
the same time purchase a round glass rod, 3/8 inch diameter by 5 inches
long; a sheet or two of tinfoil, and sixpennyworth of amalgam. From
a carpenter or timber-merchant you will require a base-board for the
machine, say 13 inches by 8 inches, by 1 inch thick, and of heavy wood;
also two uprights, which are to stand on the base-board to support the
cylinder. These may be 6 inches tall, by 2 inches by 3/4 inch.
Having now the principal parts of the frame, the work of fitting
together can be begun by making a circular hole (centre about
1-1/4 inches from the end) in one wooden upright, to take easily
one of the projecting glass pieces, or pivots, at the ends of the
cylinder--probably 3/4 inch diameter will do. This hole may be
made with a brace and suitable bit, or failing that, with a round
chisel--taking care not to split the wood. In one end of the other
upright cut a slot of same width as the hole, the bottoms of both being
on the same level. Then rest the two glass pivots in the hole and slot,
holding the uprights vertically on the base-board, when the cylinder
should be quite horizontal. If it is not so, deepen the slot, or
shorten either upright, as required. Drill a hole through the two sides
of the slot at the top, and insert a round nail to keep the pivot from
having too much play.
It will next be necessary to secure these supports to the board, which
may be done by driving stout screws from below, together with the aid
of some strong glue. If you have the skill it will be better to sink
the supports 1/2 inch into the surface.
The position should be such, that the cylinder is not quite over the
middle of the board. (See illustrations.) Next remove the cylinder by
a little side working, and screw a piece of wood, 1-1/2 inches by 1/4
inch by about 7 inches, to the supports and base. This is to act as a
brace to the supports, and also for holding tightening screws for the
rubber.
We now come to the preparation of the rubber, which is an important
detail. Get a wooden block 1-1/4 inches by 1/2 inch and 1 inch shorter
than the cylinder. Smoothe off all the corners, and glue on one long
edge, a piece of thin leather (chamois will do); fold over the flat
side, and then glue it again at the other long edge; double it back
_loosely_, and glue again in original place. This should make a sort of
bag on one side of the block, which should now be stuffed with _dry_
wool or hemp, and the two ends fastened down. A piece of black silk,
about 5 inches by 9 inches, must be attached to the bottom edge.
[Illustration: FRONT VIEW, SHOWING RUBBER SEEN THROUGH CYLINDER;
CONDUCTOR REMOVED. A A Supports; R Rubber; B Brace Board; C C Adjusting
Screws; F Rubber Stand.]
[Illustration: END VIEW. H Handle; D Conductor; E Glass Support.
RUBBER, SILK FLAP AND SUPPORT. A HOME-MADE ELECTRICAL MACHINE.]
Now place the cylinder on its bearings, and press the rubber against
the middle of one side, which will show what length to make the rubber
stand. The thickness may be 1/4 inch, and the breadth 2 inches; one end
being screwed to the rubber block at the back, and the other resting
on the base-board, but attached to the brace piece by two bolts with
adjustable nuts. These you can get at an ironmonger's--thumb nuts are
preferable, as they can be tightened up without pliers.
As this board will be on a slope, the cushion block must be bevelled
off with a chisel, so that it may rest "squarely" against the glass.
The adjusting screws will enable the pressure on the glass to be
regulated. Be careful to see that the silk flap (attached to the bottom
edge of the rubber) comes _between_ the leather and the cylinder, and
then folds over the cylinder to about the middle of the opposite side.
We next come to the "prime conductor," which is a piece of rounded
wood, 2 inches in diameter and 1 inch less than the length of the
cylinder. The end corners must be made round with a knife and
sandpaper, so the whole surface may be quite smooth. Then lay on
_evenly_ with paste, a sheet of tinfoil, notching it so that it may
fold nicely over the spherical ends, and take out any ridges by rubbing
with the knife handle.
An insulating support must be given to the conductor, as it is to
hold the accumulated electric energy, and for this the glass rod
above mentioned is required. Make a suitable hole in one side of the
conductor, and in it fix one end of the rod with cement. The other end
can be fixed to the base-board in the same way; or a separate stand
may be used; but before doing this, drive a horizontal row of strong
pins along a side of the conductor, at right angles with the rod. These
should be 1/4 inch apart, starting and finishing 1/4 inch from where
the surface becomes spherical at the two ends; the heads should be cut
off previously with pliers, and the external length, when driven into
the wood, should not exceed 1/2 inch. Now erect the conductor, and see
that the rod brings it level or thereabouts with the centre line of the
cylinder-side. The points should not quite touch the latter; and the
silk flap must not hang down far enough to come between.
There remains now but one piece of mechanism to construct--the
handle. This is apt to give trouble at first, but with care may be
successfully completed. A short piece of hard wood (say 2-1/2 inches
long), half of circular and half of square section, must be procured,
and the rounded half cemented into one of the glass pivots. This
must be done with good cement and both the glass and wood warmed,
and cleaned first of all. Be careful not to crack the glass by too
rapid heating. A thin layer of cement is best, while, of course, the
wooden rod ought to fit closely. The square end now projecting must
be provided with a handle, the making of which will serve to pass the
time during which the cement is drying. Cut a square hole to fit the
end in a piece of wood say 1/4 inch by 2-1/2 inches by 1 inch, which
is the handle shaft. Pass a bolt through the lower part and secure
the handle-bobbin itself by a nut. If nothing else can be got, a
cotton-reel makes a fair handle when the flanges are cut off. If the
nut works loose, pinch the threads at the end of the screw, or add a
"lock nut"--_i.e._ an extra nut. Dry the cylinder and put a wooden
stopper in the other glass pivot to keep out damp.
Take care to have the handle on the right-hand end of the machine when
the rubber is closest to you and the conductor opposite; notice also
that of the supports the _slotted_ one should now be on the _left_-hand
side.
All the woodwork, as well as the ends and pivots of the cylinder,
and the glass rod should be painted with shellac varnish, which may
generally be had ready mixed from paint merchants, or may be made
at home by dissolving shellac in methylated spirits. A stick of red
sealing-wax gives a more pleasing colour for the glass work if added to
the shellac solution.
All through the construction of the machine must be borne in mind the
fact that rough edges or points "attract" away the electricity, and,
therefore, all the edges and corners must be well rounded off and
smoothed with sandpaper, and everything must be kept clean and free
from dust.
When the shellac is dry, let all the parts, especially the rubber,
cylinder, and rod, have a good warming before the fire. Then fixing
the cylinder in its place, press the rubber firmly against it by means
of the adjusting screws. After turning for a few minutes, the handle
should become stiffer, and a small spark be obtained on touching the
conductor. If not, tighten up the screws a little more. It is also
advisable to lay a little amalgam with tallow on the rubber, _between_
the silk and the leather: a piece of tinfoil is also said to be of
advantage when amalgam is not handy. Sometimes, too, a wire connection
from the back of the cushion to a neighbouring gas or water pipe helps
the success of the machine, but if proper attention be paid to warming
and cleaning and the avoiding of edges and corners, success is almost
certain after a short time. A delicate test is to observe whether a
thread is attracted by the conductor, and if so, a spark may be soon
looked for.
An iron clamp or two will be found of great assistance for holding down
the base-board to the corner of a table.
$The Indestructible Candles.$--When a candle burns, the matter of
which the candle is composed, is not lost nor destroyed. It is simply
changing its form, and every part of it may be accounted for.
If we take a cold clean tumbler and hold it over the flame of the
candle (Fig. 1) we shall see that the inside becomes moist with water,
and on touching it our fingers are made wet. On the tumbler becoming
warm, this moisture disappears. If we could surround the tumbler
with an ice jacket, we should see the water from the flame of the
candle dripping down, and if this were caught in a vessel we could
obtain from an ordinary candle about a wine-glassful of water. We may
therefore produce water from a burning candle. The cause of the water
being formed is that there is in the fat of the candle, as one of its
constituents, hydrogen, and as the candle burns, this unites with the
oxygen of the air to form water. Wherever water is found it always
consists of hydrogen and oxygen in combination, and of nothing else.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
[Illustration: FIG. 7.]
[Illustration: FIG. 6.]
[Illustration: FIG. 8.]
$Presence of Hydrogen Proved.$--We may prove the presence of hydrogen
gas by bringing a lighted taper within two or three inches of the
wick of a candle just after it has been extinguished. On holding the
lighted taper in the stream of smoke coming from the wick, we shall see
a tiny flame run down the smoke and re-light the candle. The hydrogen
gas coming from the hot fat is being carried off in the smoke. It is
very inflammable, and the flame from the taper ignites it, and in turn
rekindles the candle. When the stream of smoke has ceased, it does
not matter how near we hold the taper to the wick without actually
touching, it will not be re-lighted. (See Fig. 2.)
$The Hydrogen Located.$--A still better way of showing the presence of
this gas is by bending a piece of glass tubing of small-bore, into the
shape shown in Fig. 4.
Glass tubing may be bent easily to any shape by holding it in the flame
of an ordinary gas burner. The tube becomes covered with soot, and this
prevents its getting hot too rapidly, and so enables the tube to bend
easily and evenly. The bending must never be forced, but very gently
done as the glass softens. (See Fig. 3.) A little practice will enable
any boy to make a first-rate bend.
On carefully observing the flame of the candle we shall see that it
really consists of three distinct parts. Round the wick it looks black,
this is really a hollow chamber filled with unconsumed hydrogen. Next
to this is a bright luminous cone, and outside of that is an almost
invisible covering of blue flame. In the black space gas is unconsumed,
in the luminous part the combustion is only partial, but outside of
all, where there is most oxygen, the combustion is complete, and the
flame can hardly be discovered. Now when the flame is quite steady the
tube must be gently inserted at an angle into the black cone; after a
few minutes, on applying a light at the end of the tube, although the
candle is still burning, we shall see that this free hydrogen will burn
there too with a small bluish flame.
$The Candle's Carbon.$--As the candle burns, another part of its
constituents is passing off into the air as soot or carbon, and this
can be shown by holding a sheet of white paper or cardboard in the top
of the flame, or better still, a cold saucer, on which there will be a
copious deposit of black soot. This is another proof that as a candle
burns it is not destroying matter, but only changing its form; from
the white fat of the candle, black sooty carbon is liberated by the
process of incomplete combustion that is going on. (See Fig. 5.)
$Carbonic Acid Gas.$--When substances containing carbon are burnt, one
of the products is an invisible gas, commonly called carbonic acid
gas. After an explosion in a mine, all the workings are filled with
a deadly gas, which often kills more men than the explosion. This is
called choke damp, and is the same as carbonic acid gas. Whenever a
fire burns--gas, lamp, coal fire, or candle, this gas is one of the
products. Let us fasten a piece of wire round our candle, and, after
lighting it, lower it down into a glass bottle with a wide mouth.
At first the candle burns dimly, and then, when a current of air is
established, brightens. Now cover the mouth of the jar with a piece of
card or the hand, and we shall see that the candle again burns dimly
and quickly goes out. The jar now contains a considerable quantity of
this carbonic acid gas. We may prove its presence by pouring into the
jar a little clear lime-water and shaking it up. The carbonic acid gas
will turn the lime-water milky. (See Fig. 6.)
Lime-water can be purchased at any chemist's very cheaply, or it can
be made by pouring water on a piece of quicklime, well shaking it, and
then allowing it to settle. The clear lime-water may then be poured
off. The lime may be used again and again until it is all dissolved.
$Our Use of Oxygen.$--We are breathing out carbonic acid gas; and
on breathing through a piece of glass tubing into some of the clear
lime-water we shall see that it will be turned milky in just the same
way as when the candle burned. We are using up oxygen to support
life, the candle uses up oxygen to support life, and in both cases
the product is carbonic acid gas, as we have proved by means of the
lime-water test. (See Fig. 7.)
$Convincing Proof.$--All that we have done up to the present supports
our statement that the matter of the candle is not destroyed. In fact
we have accounted for all its parts excepting that of a little mineral
ash which will be left after the candle has burned away. We may,
however, show in a very convincing way that our contention is true. An
ordinary gas chimney is obtained, and at about three inches from one
end a piece of wire gauze is placed, and the open end filled up with
quicklime, at the lower end a cork is fixed upon which a short piece
of candle is placed. There must also be a hole in the cork for the
admission of air; when all is ready, carefully counterpoise the scales.
Then remove the cork and light the candle and quickly replace. After
burning a short time it will be found that the chimney glass bears
down the beam because of increased weight. The products of the burning
candle have united with the oxygen of the air, and these products,
consisting chiefly of carbonic acid gas and water, have been caught by
the quicklime. Because of the added oxygen they are heavier than the
original candle. (See Fig. 8.)
$Capillary Attraction.$--There is still one interesting thing to
illustrate about the burning candle, and that is the way in which
the particles of fat ascend the wick to reach the flame. This is
accomplished by what is known as capillary attraction. A very good
illustration of this is afforded by a piece of salt standing upon a
plate, on which is poured some salt water coloured blue with indigo or
ink. The liquid will rise up the pillar of salt, and eventually reach
the top. It rises by the force of capillary attraction. Let the pillar
of salt represent the wick of the candle, and the coloured water, the
fat, and the illustration is complete.
$Analysis of Candle Flame.$--Our candle can still give us some useful
and suggestive illustrations of flame and combustion. We have seen that
unconsumed gaseous vapours can be obtained from the flame by means
of a bent glass tube. In the candle flame (Fig. 9) we see that this
is because of the way the flame is built. The part marked _o_ is the
gaseous chamber, _i_ is the luminous part, and _e_ is where combustion
is complete. On taking a sheet of clean white paper and pressing it
down on the candle flame for a moment or two we shall get the fact of
this hollow chamber demonstrated by the smoke ring upon the paper,
which will appear thus--
The paper is left clean at the hollow chamber, but marked with smoke at
the luminous part of the flame. (See Fig. 10.)
[Illustration: FIG. 9.]
[Illustration: FIG. 10.]
[Illustration: FIG. 11.]
[Illustration: FIG. 14.]
[Illustration: FIG. 13.]
[Illustration: FIG. 12.]
Now we must find the differences between the non-luminous outer
flame and the luminous inner flame. To do this thoroughly we must
have a Bunsen burner to afford the best illustration. This is not an
expensive item. A cheap and simple form of it can be obtained for 1s.
3d. To understand the nature of the flame we must first understand the
principles of the Bunsen. It is a burner in which a mixture of air and
gas is consumed. A is a brass tube, mounted on a solid foot K, with a
small tube C to admit the gas. There are two holes at the bottom of the
brass tube to admit air in the direction of the arrows, and a movable
brass collar fits over these holes, so that the air can be admitted or
excluded at will. On igniting the gas, with the holes of the Bunsen
open, we shall see that it burns with a non-luminous but exceedingly
hot flame. On closing the holes we shall notice that the flame becomes
luminous, much more languid, and does not give off nearly so much heat.
(See Fig. 11.)
We must ask ourselves the question, What is the cause of this
difference? The answer is a simple but very instructive one. Coal-gas,
like the fat of the candle, contains carbon, and in the luminous flame,
owing to the limited supply of oxygen, these particles of carbon are
made white hot, and so emit light, but are not entirely consumed till
they reach the outer edge of the flame, where combustion is more
complete, owing to the contact of the flame with the air, and even then
many of them escape; and so where gas is burnt the ceilings after a
time become blackened.
In the non-luminous flame, owing to the air being admitted and mixed
with the gas, the increased supply of oxygen renders combustion more
complete, greatly increases the heat of the flame, but renders it
incapable of giving light. Now, the reasons for the differences of the
two flames are made clear.
A very clever modification of this principle has been utilised in what
is known as the Argand burner, in which the gas and air are not mixed
as in a Bunsen, but the burner is made circular, and the air is made to
pass up the centre of the flame, so that it gets its supply of oxygen,
burns steadily, and presents a very large surface of luminous flame.
(See Fig. 12.)
$A Pretty Experiment.$--Let us now go back to our candle flame. We
see that it gives light, emits smoke, and does not yield a very
large amount of heat. We have learnt that it gives light because the
particles of carbon are heated to a white heat, but not entirely
consumed. These particles in the flame are held very closely together,
and so present a continuous surface. If we could get inside the flame
and scatter them we should have a pretty shower of glowing sparks.
We can illustrate this by the following experiment. Take as much
gunpowder as will rest on a sixpence, and a like quantity of iron
filings, mix them together on a small tin dish. (See Fig. 13.)
This must be done carefully and without friction. Then ignite with a
taper. The gunpowder burns, makes the particles of iron red hot, and
scatters them in a beautiful shower of glowing sparks. This is a fair
representation of pulling a candle flame to pieces, the only difference
is that the glowing particles are of iron instead of carbon.
$Artificial Lightning.$--This may be further illustrated by putting
a flame together. We may accomplish this by passing any very fine
particles of carbonaceous matter through a non-luminous flame, and we
shall see that whilst these particles pass through the flame it will
give light owing to their presence.
We require a little lycopodium, a piece of glass tubing one foot long,
and about a quarter-inch bore, and the non-luminous flame of the Bunsen
burner or a spirit lamp. Insert into one end of the tube a little of
the lycopodium powder, and then, pea-shooter fashion, apply the mouth
to the other end of the tube, and blow the contents into the flame.
There will be a great flash of light whilst these infinitely small
particles are passing through the flame, thus establishing the fact
that luminosity is due to the presence of unconsumed solid matter in
the flame. This experiment is sometimes called "making artificial
lightning," and in a dark room it is very effective. (See Fig. 14.)
$Flames that Laugh.$--What makes the candle flame burn steadily is the
next problem before us, and we shall see that it is very simple and at
the same time most philosophical. It tells us the reason why candles
are made round, and not square. The section of a candle being circular,
with the wick in the centre, it can, as it burns, get its supply
of oxygen from all directions at an equal distance; thus it burns
regularly and steadily. If the candle were square, the four corners
being at a greater distance from the wick than the sides, we should
have four columns of fat standing up at the corners, and as the air
rushed in to feed the flame it would come into contact with these, and
so the current would be broken and the flame would become unsteady. We
can show this by placing some cotton wool on tin dishes, and saturating
it with methylated spirits and igniting it. This will give us what are
known as laughing flames, because they burn so unsteadily. The air
rushing in to feed the flame comes into contact with the wool, which
impedes it, and so the flame has a dancing or laughing appearance. This
experiment may be made very pretty by rendering the flames coloured.
To do this add to the cotton wool, before pouring on the methylated
spirit, chloride of copper; this will give a green flame; to another,
chloride of strontium; this will colour the flame red; to another,
common salt; this will give a yellow coloration. All these should be
shown in a dark room.
$The Importance of Oxygen.$--By previous experiment we have seen that
oxygen is necessary to a flame, and our ingenious readers may now make
a piece of apparatus to prove this. (See Fig. 15.) It consists of two
pieces of glass tube standing upright near the two ends of a board, in
which there is a covered channel communicating with the two. A small
candle is lighted and placed in one of the tubes. The air heated by the
flame rises in the tube and causes a corresponding descent of cold air
down the other tube. This gives us a good illustration of ventilation
produced by artificial heat. So great is the down draught, that if we
hold a lighted taper over the mouth of the cold tube the smoke and the
flame will be carried down, with the result that the candle is soon
extinguished. The reason for this is that the smoke and burnt air
from the taper contain insufficient oxygen to feed the candle flame,
and it dies. To make this apparatus, obtain a piece of deal board
about ten inches long and four inches wide, cut along the middle a
groove about three quarters of an inch deep, and about the same width,
leaving about half an inch at each end uncut. Cover this groove with
a tightly-fitting slip. Over the two ends of the groove are fastened
two small blocks of cork pierced with apertures, into which fit the
vertical glass tubes; these should be about ten inches high and about
three-quarters of an inch bore. Fig. 16, which is a section of one end
of the apparatus, shows how a small candle like those used on Christmas
trees is held erect by a wooden socket at the end of the groove so as
not to impede the current of fresh air.
$Rates of Combustion.$--We must remember that all things do not burn
at the same rate. Iron rust is a product of very slow combustion. In
using up food to maintain the heat of the body, combustion goes on more
quickly than in rusting iron, the candle burns more quickly still, gas
still faster, the Bunsen burner faster still. We may get an idea of
the different rates of combustion by the two following experiments. On
a tin dish place half a thimbleful of gunpowder and lay on it a tiny
piece of gun-cotton. Ignite the gun-cotton; it burns so fast that it
has no time to set fire to the gunpowder, which may now be ignited in
its turn by the taper. Another example is the laying of two long trains
of gunpowder, one fine grain and the other coarse. It will be found
that the two flames travel at very different rates along the same path.
$The Egg and Bottle Trick.$--An ordinary water-bottle, a hard-boiled
egg, divested of its shell, and a piece of thin paper are all that is
requisite. How can we make this egg get inside the bottle? Light the
paper, quickly thrust it into the bottle, and immediately place the egg
over the mouth of the bottle, gently pressing it closely down to the
glass. The burning paper consumes some of the air, a partial vacuum is
formed, and air pressure will force the egg into the bottle with a loud
detonation. (See Fig. 17.)
$Making Water Boil by Means of Coldness.$--Heat some water to boiling
in a glass flask over a spirit lamp. After the water has boiled for a
minute or two, quickly insert a well-fitting cork, and remove the flask
from the flame. Wrap a duster or towel round the neck of the flask,
and, holding it over a basin (in case of breakage), pour gently a
stream of cold water on to the flask. The steam inside is condensed, a
partial vacuum is formed, and as long as any heat remains in the water,
it will boil, whilst the stream of cold water is continued on the
outside. When ebullition no longer occurs, it will be found that the
cork is held in so tightly by air pressure that it is very difficult to
draw it. (See Fig. 18.)
$Fire Designs.$--This is very simple, amusing, and effective. Make a
saturated solution of nitrate of potash (common nitre or saltpetre), by
dissolving the substance in warm water, until no more will dissolve;
then draw with a smooth stick of wood any design or wording on sheets
of white tissue paper, let it thoroughly dry, and the drawing will
become invisible. By means of a spark from a smouldering match ignite
the potassium nitrate at any part of the drawing, first laying the
paper on a plate or tray in a darkened room. The fire will smoulder
along the line of the invisible drawing until the design is complete.
(See Fig. 19.)
$The Magic Wine Glass.$--The holding of a wine-glass to a substance
mouth upwards without its falling off, may be accomplished thus. Obtain
a wine-glass with a very even edge (this may be done by grinding on a
flat stone), a square of blotting-paper, and a piece of glass. About
half fill the glass with water, place upon its rim the blotting paper,
and then the piece of glass. Whilst pressing them closely down invert
the glass. The blotting-paper absorbs some of the water, a partial
vacuum is formed, and on holding the sheet of glass, the wine-glass
will remain suspended, being held on by atmospheric pressure. (See Fig.
20.)
[Illustration: FIG. 15.]
[Illustration: FIG. 17.]
[Illustration: FIG. 16.]
[Illustration: FIG. 18.]
[Illustration: FIG. 19.]
[Illustration: FIG. 20.]
$The Floating Needle.$--The idea of making a needle float upon water
at first sight seems an impossibility but it can be done, and that
with comparative ease. Take a fine needle, and rub the fingers over
it gently to grease it. Now lay it very carefully on a piece of thin
tissue paper on the surface of the water, as shown. Presently the paper
will sink, and leave the needle floating on the water. The thin coating
of grease serves to protect the needle from actual contact with the
water, and thus enables it to float. (See Fig. 21.)
$A Glass of Water Turned Upside Down.$--A tumbler is filled with water,
a piece of paper laid on, and the surface and the tumbler deftly
inverted, the atmospheric pressure being unable to enter the glass,
the water is kept in, so long as the paper holds. The effect of the
experiment is very greatly increased, if, instead of using paper, a
piece of thin mica, cut to the size of the glass, is used. The audience
cannot then discover what prevents the water from running out. Any
gasfitter will supply a piece of mica.
$The Inexhaustible Bottle.$--This wonderful bottle, from which five
separate liquids can be poured, owes its marvellous qualities to the
application of the simple law of atmospheric pressure. It is made of
tin, and encloses five internal cylinders, each of which has a tube
from the upper end running into the neck of the bottle, and another
tube from the lower end opening into the side. The cylinders are filled
with different liquids--water, milk, tea, coffee, lemonade. Whilst the
fingers are kept over the holes the bottle may be inverted, and nothing
will run out. On opening the holes one by one the liquid may be poured
out, according to the wishes of the audience, and greatly to their
astonishment. (See Fig. 22.)
$The Magic Writing.$--Fill a deep tumbler with water, and add a few
crystals of iodide of potassium and a few drops of sulphuric acid. The
liquid will remain perfectly clear like water. On some strips of white
cardboard write various names with starch paste; when dry these will
be invisible. On dipping the cardboard into the liquid the name will
appear in blue writing, owing to the formation of starch iodide, which
is blue. By previously preparing the names of those present at the
experiment, by a little manipulation you can, to the astonishment of
the audience, produce any name called for.
[Illustration: FIG. 21.]
[Illustration: FIG. 22.]
[Illustration: FIG. 25.]
[Illustration: FIG. 23.]
[Illustration: FIG. 24.]
$Producing Smoke at Will.$--Two glass cylinders are the best for this,
but ordinary tumblers will do. With a separate feather make the inside
of each tumbler quite wet, one with hydrochloric acid, and the other
with liquid ammonia. Both glasses appear to be quite empty, and nothing
occurs. But on bringing the mouths of the two vessels together, a thick
white smoke is at once developed. The hydrochloric acid gas and the
ammonia gas unite chemically, and form the solid white powder known as
sal-ammoniac. (See Fig. 23.)
$A Novel Fountain.$--This is a pretty experiment, and owes its action
to the fact that ammonia gas is very soluble in water. In a basin place
some water. Fit up a flask with a small-bore glass tube, about eighteen
inches long, as shown. The end entering the flask should be drawn
out so that there is only a small opening. In the flask place about
a teaspoonful of liquid ammonia, and heat it over a spirit lamp. As
soon as the liquid boils a large amount of ammonia gas is disengaged,
and fills the flask and the tube. Now close the tube by means of the
finger, and invert the flask over the basin of water. When the end of
the tube is under the water remove your finger, and then, as the water
dissolves the gas, it will rise in the tube, and will presently play
into the flask like a fountain until the flask is full. (See Fig. 24.)
$To Boil Water in a Paper Bag.$--"Here is a sheet of note-paper; can
you boil me a little water in it?" This would appear to be a thorough
puzzler, yet it is exceedingly easy to do. Fold a piece of paper so
that it will hold water, now suspend it above the flame of a lamp. The
water will so readily take up all the heat that there is none left with
which to burn the paper, and presently it will bubble and give off
steam. (See Fig. 25.)
$Illuminated Water.$--Wet a lump of loaf sugar with phosphorized ether,
and throw it into a basin of water in a dark room. The surface of
the water will become luminous. Blow on the water, and you will have
phosphorescent waves, and the air, too, will be illuminated. In winter
the water should be warmed a little. If the phosphorized ether be
applied to the hand or to other warm bodies these will become luminous.
The ether will not injure the hand.
$Brilliant Crystals.$--Spread upon a plate of glass or upon a smooth
slate, a few drops of nitrate of silver, previously diluted with double
its quantity of soft water. Place at the bottom of it, flat upon the
glass, and in contact with the fluid, a copper or zinc wire, bent
to any figure, and let the whole remain undisturbed in a horizontal
position. In a few hours a brilliant crystallization of metallic silver
will make its appearance around the wire upon the glass, and this
arrangement of crystals will extend gradually till the whole quantity
of fluid has been acted on by the wire.
$A Well of Fire.$--Add gradually one ounce, by measure, of sulphuric
acid, to five or six ounces of water in an earthenware basin; and add
to it also, gradually, about three quarters of an ounce of granulated
zinc. A rapid production of hydrogen gas will instantly take place.
Then add, from time to time, a few pieces of phosphorus of the size of
a pea. A multitude of gas bubbles will be produced, which will fire on
the surface of the effervescing liquid; the whole surface of the liquid
will become luminous, and fire balls, with jets of fire, will dart from
the bottom through the fluid with great rapidity and a hissing noise.
$The Writing on the Wall.$--Take a piece of phosphorus from the bottle
in which it is kept, and, while the room is lighted write upon a
whitewashed wall any word or sentence, or draw any object. Now put out
the light, and the writing will appear in illuminated letters. Care
must be taken to dip the pencil of phosphorus in cold water frequently
while you are using it. Otherwise it will burn.
$To Make a Ghost.$--Put one part of phosphorus into six of olive oil,
and let it dissolve in a slightly warm place. Shut your eyes tightly
and rub the mixture upon your face. In the dark your face will be
luminous, your eyes and mouth like dark spots. Altogether you will have
a very ghastly appearance. There is no danger in the experiment, and
the effect might be useful in charades or home theatricals.
$A Seeming Conflagration.$--Take half an ounce of sal-ammoniac, one
ounce of camphor, and two ounces of aqua vitae. Put them into an
earthen vessel that is small at the top. Set fire to the contents, and
the room will seem to be on fire.
$Three Haloes.$--One of the pleasing experiments of Dr. Brewster was to
take a saturated solution of alum, and having spread a few drops of it
over a plate of glass, it will crystallize rapidly though the crystals
are so small you may scarcely see them. When this plate of glass
is held between you and the sun or artificial light, with the eyes
very near to the smooth side of the glass, there will be seen three
beautiful haloes of light.
$Beautiful Crystals.$--Pour three ounces of diluted nitric acid into
a glass vessel, and add gradually to it two ounces of bismuth, broken
by a hammer into small pieces. The metal will be attacked with great
energy, and nitrate of bismuth will be formed. Crystallize the solution
by a gentle heat, and preserve the crystals, which possess great
beauty, under a glass.
$The Centre of Gravity.$--A shilling may be made to balance on the
point of a needle with very simple apparatus. Put a bottle on the
table with a cork in its neck; into the cork stick a middle-sized
needle in an upright position. In another cork cut a slit, and insert
the shilling, then into this cork stick a couple of forks, one on
each side, with the handles inclining outwards. Now poise the rim of
the shilling upon the point of the needle, and it will rotate without
falling. So long as the centre of gravity is kept within the points
of support of a body it cannot fall. The balancing shilling may be
transposed to the edge of a bottle, and it will still perform, even as
the bottle is being tilted.
$What a Vacuum Can Do.$--Take a new or nearly new penny and rub it
briskly upon your coat sleeve until it is warm. Then slide it up and
down upon a door panel, pressing it closely to the wood. Now hold it
in one place for a few seconds and you will find it will stick there,
because between the penny and the surface of the door there is a layer
of air which was slightly heated. As it became cool a partial vacuum
was formed, and the pressure of the outer air held the penny to the
door.
$An Experiment in Leverage.$--It would seem almost impossible that a
column of iron or a plank or a spar of any kind could be so placed
that one end of the spar needs support only, whilst the other end
would extend from, say the edge of a precipice, horizontally into
space; but that such can be done is very easily demonstrated, by very
simple materials almost always at hand. By adopting the principle we
may easily perform an interesting scientific parlour experiment, which
always causes difficulty to the non-studious section of humanity, until
the apparent mystery is explained.
In illustrating this experiment the prongs of two ordinary table forks
are fastened together, one over the other--net fashion--thus causing
the handles of the forks to form the termini of an angle of about 45
degrees. Now take an ordinary lucifer match and place one end between
the network of the prongs firmly. Then place the other end of the match
upon the edge of an elevation, such as a tumbler or cup, when the
match, acting as a lever, with the forks giving a hundred or a thousand
times additional weight to the lever, will rest (or apparently float in
the air) without further support.
Ask your friends to try the experiment, after placing the materials
before them, and find how many can perform it without guidance.
$Coloured Fires.$--It is perilous to make some coloured fires,
especially those in which there is sulphur, and even if they do not
explode their fumes are harmful, so that their use in the house
for charades or other home purposes is objectionable and at times
positively dangerous. We give, however, a number of coloured fires
that are free from these drawbacks, though all the same it is wiser
to reduce the ingredients to powder quite separately before they are
mixed, and if a pestle and mortar are used all traces of one powder
should be removed before another is introduced. Each ingredient should
be reduced to a fine powder.
RED FIRE.
Parts.
Strontia 18
Shellac 4
Chlorate of Potash 5
Charcoal 4
GREEN FIRE.
Nitrate of Barytes 18
Shellac 4
Calomel (Chloride of Mercury) 4
Chlorate of Potash 2
GREEN FIRE.
Nitrate of Barytes 9
Shellac 3
Chlorate of Potash 12
Charcoal 4
BLUE FIRE.
Parts.
Chlorate of Potash 14
Salpetre 6
Ammonia Sulphate of Copper 6
Arsenite of Copper 6
Shellac 2
BLUE FIRE.
Ammonia Sulphate of Copper 8
Chlorate of Potash 6
Shellac 1
Charcoal 2
RED FIRE.
Nitrate of Strontia 9
Shellac 3
Chlorate of Potash 1-1/2
Charcoal 4