Part 2

A most interesting class of experiments can be made with an air pump, a piece of apparatus unfortunately beyond the pocket-money supply of the average boy. Nevertheless, if the following instructions are exactly followed and carefully carried out, a very excellent air pump can be made at a comparatively small cost. Some pretty, as well as interesting results will amply repay you for the trouble you take to make the pump. Although the air seems so light in comparison with water or a heavy metal like iron, you must remember that it really presses upon every square inch of the earth’s surface, aye, on every square inch of your own bodies, with a force of fourteen and a half pounds. In other words, the weight of the air at the sea level resting on each square inch of surface weighs fourteen and a half pounds.

Don’t be frightened, boys, at the explanation of one word that must be used in connection with air experiments. The word is vacuum. Vacuum really means an empty space, devoid of all matter, even of air. Although it seems easy to think of an empty space, it is quite impossible to exhaust a space of all matter, even of air. For this reason, the alchemists of the middle ages used to say: “Nature abhors a vacuum.” This was only their way of saying how impossible it was to make a space, such as the inside of a vessel, quite empty. Yet it is possible to reduce the amount of air in a vessel almost to nothing.

Now for the pump. In the first place obtain three pieces of gutta-percha tubing of the following lengths:

No. 1.--A tube twelve and a half inches long, measuring outside two and a half, inside one and a half inches in circumference.

No. 2.--This must be seven and a half inches long, one and a half inches outside, and an inch inside.

No. 3.--This is a length of tubing about sixty inches long, two and a half inches in outside circumference, and at least an inch thick. If an inch and a half thick all the better, as it will be more air-tight.

Divide tube No. 2 into two equal parts, cutting from right to left at an angle of 45 degrees. Into one of the parts fit a plug of hard wood pierced lengthwise by a red hot wire (fig. 1); the figure shows the shape of it sufficiently. In the hollow side cut a small opening, and over this tie very tightly a band of flexible india-rubber (fig. 3). This band will serve as the valve of the piston of the pump. Figs. 3 and 4 give a side and front view of this valve. Great care must be taken neither to split the plug in boring the hole nor to cut the tube.

This valve must now be inserted in the large tube No. 1, as seen in fig. 2.

At the other end of the large tube, which will serve as the body of the pump, at B fig. 2, fix a similar valve to the above, but the india-rubber band must be fixed on the other side of the valve as at B fig. 2. The fitting A will serve for escape, the second for withdrawing the air from the space to be exhausted. Finally fix tube No. 3 on valves A or B, fig. 2, according to your wish to produce a vacuum or to compress the air.

By means of a pedal made simply with two boards put together on hinges (fig. 5), one pressed with the foot, the air contained in the body of the pump (fig. 2) tends to escape. It therefore lifts the valve of the fitting fixed at A, and escapes through the flexible elastic band tied over the hole in the hollow side of tube No. 2. If the pressure ceases the big tube, on account of its own elasticity, takes its former form and sucks in the air. This time it is the valve at B which is lifted and lets pass the air which fills the body of the pump. If one has fixed on to the fitting at B, the long india-rubber tube No. 3, which is plunged in a receiver--a receiver is any vessel in which the air is exhausted, or into which it is forced--it is easily understood that after a few moves of the pedal, the air is drawn out, and a vacuum is obtained.

If one wishes to have a force-pump one has only to modify slightly the construction of the valve. Instead of a band of india-rubber fixed as shown in fig. 3, it is altered as in fig. 4, that is to say the valve is formed by a band of supple india-rubber fastened by two tacks only on one side of the opening in the side of the plug. For this object it is also necessary to take stronger tubes.

Let us now review the few experiments that can be made with this machine.

In order to conduct experiments a receiver must be obtained. The best vessel for your purpose is a large bell-jar with a ground glass stopper and neck to insure absolute tightness. Such a jar may be cheaply obtained at a scientific instrument maker’s for about seventy-five cents. If you cannot get a bell-jar procure a 4-lb. jam pot and a tightly-fitting bung. In the middle of the latter bore a hole to admit a glass tube, some six inches long and an inch in diameter, and then sealing-wax the whole of the upper surface of the bung so that air cannot enter. Over the projecting end of the glass tube, bind very tightly the free end of the long tubing affixed to the pump. To ensure tight binding, waxed thread should be used.

Asphyxia.

Put a mouse--it is necessary to catch him first--into the receiver, and work the pump. Soon the animal will show all the signs of being choked, and eventually will die. This is proof sufficient that animals cannot live without air.

Balloon in Vacuum.

Place in the receiver a small bladder, such as are sold in the streets for a few cents. Wet it a little to make it more supple. Now, in the ordinary way the air inside the bladder exerts the same pressure on the skin of the bladder as does the air on the outside. Now work the pedal so that the air in the receiver is gradually exhausted. The bladder will be seen to gradually swell and finally burst. It bursts because as the air in the receiver is exhausted by the pump, the air outside the bladder exerts a less force than the air inside. But the air inside is confined by the bladder skin, a not very strong material, as you know, so as soon as the difference between the inside and outside pressures is greater than the strength of the bladder, the latter bursts. This experiment also shows the expansible power of air.

Boiling Cold Water.

Place in the receiver a tumbler of cold water and work the pump as before. In a few minutes, as soon as the air is sufficiently exhausted, the water will apparently boil. Yet you know the water does not boil in a kettle unless heated to 212 degrees. This phenomenon is thus explained: The vacuum causes the air-bubbles contained in the water to escape. They easily do so, because there is scarcely any reserve on the surface of the liquid (see fig.).

A Sucking Tube.

This force, the pressure of the air which you have just ascertained, supplies various experiments in its illustration.

Take a tin tube, for example, the tin holder of a penny pen, which you may procure at any stationer’s. Put a little water in it and make it boil so that the steam takes the place of the air.

When steaming furiously stop the mouth of the tube with a small cork, sealing the opening hermetically. Oil it a little, so it may glide with ease. If you cool the tube by plunging it in a basin of cold water, for example, the steam is condensed, forming a vacuum in the interior, and under the atmospheric pressure the cork will glide down. Fasten a string to the cork and you can withdraw it and begin the operation again. As the water gets hot, steam is reformed; you will see the cork come up again.

A capital way of making this cork is to stick the tube in a piece of potato, cutting out of the latter a perfectly-fitting cork.

Cupping.

Instead of a jar-receiver, take a long-necked bottle open at both ends. If you place the hand on one of the open ends and exhaust the air, by attaching the long tube of the pump to the other you cannot remove the hand easily. Do not try to pump the air out entirely, as the suction may be too strong and draw blood. It is by the rarefaction of the air that the cupping-glass is applied to people who require bleeding. In the antiquated surgical operation of cupping, the doctor burned a few pieces of paper in small glass cups, which are then applied to the skin; the air, in getting cold, contracted and produced a partial vacuum, thus acting as the bottle did in the above experiment.

The Barometer.

Now you shall learn something about the pressure exercised by the atmospheric layer which surrounds the earth to the height of about forty miles. This is done with the aid of a very well-known instrument called the barometer.

You may construct one yourselves. Procure a glass tube closed at one end, about a yard long and one tenth of an inch in diameter. Fill it with mercury, then turn it upside down into a bowl filled with the same metal, taking care that the air does not enter the tube. The column will stop at a height between 29 and 30 inches.

This, therefore is the measure of the force of the air’s pressure, for in the upper part of the tube there is an absolute vacuum and nothing would prevent the mercury from going higher up. The weight of the air layer corresponds, therefore, to a height of nearly 30 inches of mercury.

This weight has been before stated, viz., fourteen and a half pounds, such a weight being supported by every single square inch of the globe’s surface. A marvelous pressure is thus exerted on the whole earth. In other words, the weight of the air that surrounds the earth on all sides is no less than the following enormous number of 5,184,740,000,000,000 tons.

A man of average height, himself supports the enormous pressure of 34,171 pounds, or over 15 tons, and yet does not feel the least inconvenience in his movements. It is because this pressure is exercised in all directions, and a human body carries within it elastic fluids that counterbalance that tremendous weight.

So accustomed do people become to this weight that when the weather is stormy, a feeling of heaviness comes on.

However, it is just the contrary which takes place when the barometer is lower; that is to say, the atmospheric pressure has diminished. Consequently there is less weight to be carried.

You would experience the same sensation when going up in a balloon. As you rise higher and higher the weight of the air is less felt, and this makes people so uncomfortable that at a height of about 9,000 or 10,000 yards the liquids in our body--the blood, the water, the bile--tend to escape outwards. Why? Because they are no longer balanced by an outside pressure equal in force to them. In fact, if you continued to ascend, your fate would be that of the bladder in the first experiment--you would burst. Thus are you and all creatures attached to the face of the earth, and it seems as if great heights were forbidden to our curiosity.

A Novel Barometer.

Construct a toy house of cardboard, painted, and let there be two open doorways in the front, and let it stand on a wooden platform to represent the ground. The two sides and back may come right down to the ground, but there must be a slight space between the front of the house and the ground upon which it stands.

Next make a flat wheel or disc of wood about the thickness of a penny, its diameter or measurement across the center to measure the same as the distance between the two doorways of the house. The wheel disc or turn-table must have a shaft or spindle in the middle, so that it will revolve easily in a hole made for it in the floor or ground which your cardboard house stands on; this pivot-hole should be just within the house and exactly half way between the two doors.

In the next place get two small dolls of such size that they will pass easily through the doorways, or you may cut them out of cork or some light substance. Dress one to represent an old man and the other as his wife, and fix them opposite each other at the edge of the disc or wheel in such a manner, that when it turns on its axle, the figures move in and out of the two doorways provided for their accommodation, for it appears that, although residing in the same house, they are not on very good terms. When the husband goes out the wife remains at home, and as she only ventures abroad in fine weather, her spouse is obliged to look out when rain may be expected.

The motive power has now to be provided and this takes the form of a piece of catgut, such as violin strings are made of; this is a substance very susceptible of atmospheric influences, for dry weather contracts or tightens it, while a damp atmosphere causes it to relax. Double your catgut and twist it, fasten one end of the rope so formed near the back of the house inside and fasten the other to the pivot or axle, with two or three turns round it. As the weather changes the tightening or relaxing of the rope will cause the figures to move in and out of the house. Of course, the figures must be arranged so that the lady comes out when the rope is tightened by the dryness of the atmosphere.

Compressed Air.

To make experiments with compressed air, you must put your wits together to make a reservoir. Air, you know, is a gas consisting of particles called atoms. These atoms are at a certain distance from one another. They can be pushed further from one another as when you heat them, or closer together by cold and compression. So compressed air only means air whose atoms are pressed more closely together than as the case with the air around us.

Now you have heard that a column of air on a square inch weighs fourteen and a half pounds. Also, you know that air in a receiver or any other vessel presses on the vessel inside and out with a force (or weight) of fourteen and a half pounds.

If now into the vessel you push another quantity of air, equal to the vessel’s capacity, you simply push the atoms of air closer together. In fact, they are now only half as far apart as the atoms of an open vessel. But the pressure is doubled and the compressed air, therefore, will press on the inside of the vessel with a force of twenty-nine pounds.

Now to make the reservoir. Get a tin tube about 40 inches long and four in diameter, closed at both ends. Take care that the soldering is well done. Two openings must be made, and a small tube inserted in each. To each of these attach an indiarubber tube, one four feet long, and the other six. (See fig.).

To fill this reservoir with compressed air, apply the air-pump fitted with the valve shown in fig. 4, in the description of an air-pump. Squeeze tightly the upper tube of the reservoir before beginning to pump, and then it will be easy to judge the amount of compression of the air. For the first experiment place a light ball or sheet of paper over the mouth of the tube, and loosen your hold on it. The object will immediately be blown away with considerable force.

Noiseless Bell.

We know that sound is a succession of vibrations which must be transmitted in a medium with weight, as air or water; in other words, in a vacuum there can be no sound at all. To prove this, introduce into the receiver a small bell, and as the air is extracted the sounds become weaker and weaker, and cease altogether when the air is completely rarified.

The Bursting Bladder.

Tie a thin piece of light indiarubber round the top of the bottle, and you will notice that as the air is withdrawn, the indiarubber will stretch, and at length form a round small balloon in the interior of the bottle. (Fig. 1).

If a piece of bladder is tightly stretched and tied round the vessel (fig. 2.) it will burst under the force of the atmospheric pressure which acts upon it, through a vacuum having been made underneath. This is another case of the first experiment with the air pump described above.

Weight of the Air.

Another experiment will still better make you appreciate the value of this factor: the weight of the air.

Put a piece of supple leather in which a ring is attached under the bottle; pump the air out of the latter and you will be astonished at the weight you may hang on this leather without dragging it off.

Should you not have at hand a glass receiver, a wooden reel may serve instead (see fig.). On one of its faces place a piece of strong cardboard, in the middle of which a hook has been fastened; when the rarefaction is made, rather heavy weights must be hooked on before the cardboard is detached from the face of the rest.

Spoons which will Melt in Hot Water.

Fuse together in a crucible, eight parts of bismuth, five of lead and three of tin; these metals will combine and form an alloy, of which spoons may be made, possessed of the remarkable property of melting in boiled water.

Effect of Compression.

Take a wooden reel and hollow out either the top or bottom, beginning at the hole in the center and working towards the edge. In the hollow place a ball. Apply to the other end the indiarubber tube which conducts the forced air, and the ball will be lifted up (see fig.).

To Cover Iron with Copper.

If you are about to perform a conjuring trick, you will, of course take great care that your apparatus is ready. Therefore, clean your piece of iron or steel from dirt. Dip a piece of polished iron--the blade of your knife, for instance--into a solution, either of nitrate or sulphate of copper, when it will assume the appearance of a piece of pure copper.

The Elements.

Before entering into the next series of experiments the young chemist must know that all the substances of which the world and everything in it are made up--_i.e._, the elements are arranged in two classes, the metals and the non-metals. The former are by far the more numerous, altogether numbering more than fifty. Among the better known are such well known substances as iron, mercury, copper, tin, potassium, antimony, strontium, and nickel. The non-metals are more widely distributed and together made up of the bulk of the universe.

They comprise the gases--oxygen, hydrogen, nitrogen, and chlorine, and such substances as sulphur, carbon, phosphorus and iodine. To the latter class also belongs a peculiar element called fluorine, which, when combined with hydrogen, destroys glass. It is the only liquid known which cannot be contained in a glassen or earthenware vessel, and when used for experimental purposes must be kept in a leaden bottle.

Of course it will be understood that the above is not a complete list by any means, but is sufficient to give a clear idea of the difference between the two classes. The metals generally speaking are of a more or less sparkling, lustrous appearance. The metals, too, are good conductors of heat and electricity, and generally heavy. These characteristics are almost entirely wanting in the non-metals. We shall now give some tricks with the metals.

Potassium.

Potassium was discovered by Sir H. Davy, in the beginning of the present century, while acting upon potash with the enormous galvanic battery of the Royal Institution, consisting of two thousand pairs of four inch plates. It is a brilliant metal, so soft as to be easily cut with a penknife, and so light as to swim upon water, on which it acts with great energy, uniting with the oxygen and liberating the hydrogen, which takes fire as it escapes.

Trace some continuous lines on paper with a camel’s-hair brush dipped in water, and place a piece of potassium about the size of a pea on one of the lines, and it will follow the course of the pencil, taking fire as it runs, and burning with a purplish light.

The paper will be found covered with a solution of ordinary potash. If turmeric paper be used, the course of the potassium will be marked with a deep brown color. Hence if you touch potassium with wet fingers you will burn them.

If a small piece of the metal be placed on a piece of ice, it will instantly take fire, and form a deep hole which will be found to contain a solution of potash.

In consequence of its great affinity for oxygen, potassium must be kept in some fluid destitute of it, such as naphtha acid, which has been displaced by the great affinity or liking of the oxygen and acid for the copper.

2. When the copper is no longer coated, but remains clean and bright when immersed in the fluid, all the silver has been deposited, and the glass now contains a solution of copper.

Nearly all the colors used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying color, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. All the various tints, of green, orange, yellow and red are obtained from this metal.

Solutions of most of the metallic salts give precipitates with solutions of alkalies and their salts, as well as with many other substances, such as what are usually called prussiate of potash, hydrosulphret of ammonia, etc. The colors differ according to the metal employed; and so small a quantity is required to produce the color, that the solutions before mixing may be nearly colorless.

Metallic Colors.

To a solution of sulphate of iron add a drop or two of a solution of prussiate of potash, and a blue color will be produced.

2. Substitute sulphate of copper for iron, and the color will be a rich brown.

3. Another blue, of quite a different tint, may be produced by letting a few drops of a solution of ammonia fall into one of sulphate of copper, when a precipitate of a light blue falls down, which is dissolved by an additional quantity of the ammonia, and forms a transparent solution of the most splendid rich blue color.

4. Into a solution of sulphate of iron, drop a few drops of strong infusion of galls, and the color will become a bluish black--in fact ink. A little tea will answer as well as the infusion of galls. This is the reason why certain stuffs formerly in general use for dressing-gowns for gentlemen were so objectionable; for as they were indebted to a salt of iron for their color, buff as it was called, a drop of tea accidentally spilled produced all the effect of a drop of ink.

5. Put into a largish test tube two or three small pieces of granulated zinc, fill it about one-third full of water, put in a few grains of iodine, and boil the water, which will at first acquire a dark purple color, gradually fading as the iodine combines with the zinc. Add a little more iodine from time to time, until the zinc is nearly all dissolved. If a few drops of this solution be added to an equally colorless solution of corrosive sublimate (a salt of mercury), a precipitate will take place of a splendid scarlet color, brighter, if possible, than vermilion, which is also a preparation of mercury.

Crystallization of Metals.

Some of the metals assume certain definite forms in return from the fluid to the solid state. Bismuth shows this property more readily than most others.

EXPERIMENT.

Melt a pound or two of bismuth in an iron ladle over the fire; remove it as soon as the whole is fluid; and when the surface has become solid break a hole in it and pour out the still fluid metal from the interior; what remains will exhibit beautifully formed crystals of a cubic shape.

Sulphur may be crystallized in the same manner, but its fumes, when heated, are so very unpleasant that few would wish to encounter them.