How to Do Chemical Tricks — Amateur Air Pump, Asphyxia, Balloon in a Vacuum, Boiling Cold Water, A Sucking Tube, Cupping

Amateur Air Pump.

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.

[Illustration: FIG. 1. ] [Illustration: FIG. 2. ] 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.

[Illustration: FIG. 3. ] [Illustration: FIG. 4. ] 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.

[Illustration: FIG. 5. ] 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.

[Illustration: FIG. 6. ] 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.

[Illustration] 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.

[Illustration] 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. ).

[Illustration] 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.

[Illustration] 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.

[Illustration]