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paratus possible for them and that these experiments be made a part of opening exercises. One experiment carefully made and thoroughly understood is enough for a les

son.

Will you kindly gain your own consent right now to start with me in this work? I assure you a pleasant and profitable journey.

THE AIR PUMP. TWENTY-FIVE

EXPERIMENTS.

The most interesting and useful single piece of apparatus for a school is the Air Pump. Twentyfive experiments are here given and as many more may be suggested by ingenious pupils.

7

Fig 1

These you may call your 15 pound experi ments for they all depend upon the 15 pound atmospheric pressure. To understand the philosophy of the air pump it is well that we first make and explain the common lift or "suc

tion" pump such as may be found in wells and cisterns. Pupils here see the action of the valves and the philosophy of the "suction" pump is that of the air pump.

TO MAKE A LIFT OR "SUCTION" PUMP. Secure a heavy Argand lamp. chimney, two good corks, two tacks, two pieces of leather and a

good wire or a forked stick for a piston rod. Bore smooth holes size of a lead pencil through the corks, then place the lower as shown in Fig. 1 with leather valve fastened by tack so that it covers hole through cork. Insert small glass tube or one of rubber to reach water in cistern and arrange cork for piston with valve similar to first. If necessary wrap the piston cork with thread that it may fit neatly, though not tightly. When the piston is raised a partial vacuum is formed between the corks into which the 15 pound atmosphere pressure forces the water from below. When the piston descends the lower valve closes and the upper rises to allow the water to pass above the piston. If desirable a hole may be bored with a broken file as at s and a spout placed in pump. pump. This pump will work perfectly and if your pupils understand the action of the valves they are ready to study the air pump.

TO MAKE AN AIR PUMP.*

The directions here given will enable any school to have this useful piece of apparatus at the most trivial cost. The cost need not be more than your wages for one day but the value to yourself and to your school will be many times such. price. To make this pump is the

*Twining and Gillman of Newark, O., furnish an 81⁄2 inch pump carefully tested for $1.00. They supply pump, plate and connections for $1.50, purchaser to pay expressage.

hardest task I shall ask of you and the better you succeed the greater your cause for just pride. Secure a piece of scrap plate glass seven or eight inches square from a hardware or drug store for the plate of your air pump. Through the center of this bore a smooth round hole about three-eights of an inch in di

FIG. 2. R is a receiver made from lantern globe. It is covered by a small piece of glass.

ameter using for this the rough end of a broken file held in a common

brace such as carpenters use. Keep the end of the file wet with turpentine, camphor or oil. Some emery powder added will hasten the work. It will probably require fifteen minutes to bore the hole. Then place some emery on one face of the plate and with another piece of glass grind the surface perfectly true. You will then have a better plate than if it were iron or brass as it will not corrode or rust nor will it be eaten in holes by acids. For convenience of handling, fit your plate into a little wood frame.

say two or three inches high leaving one side open that you may connect the pump. Fit in the hole of plate an inch section of rubber tubing through which pass a two inch glass tube bent at right angles. These fittings must be air tight. You are now ready for a pump. Select a good bicycle pump and if the piston is held on by a screw remove and invert the leather. You must then secure a bicycle valve, take apart and cut off from the spring enough wire that when put together you can force back the valve by blowing strongly. It is now necessary to get a 30 inch piece of inch diameter heavy rubber tube into which push your valve being careful that the valve lifts toward the piston of the pump. Then attach the pump to the tube and the tube to the glass tube in the plate when, if your fittings are all perfect, and the valves properly arranged you have in your hands a magnificent triumph in apparatus making and an appliance with which you can make many delightful and useful experiments.

TO MAKE RECEIVERS.

Grind all vessels from which you wish to exhaust the air on an extra piece of glass being careful to see that the rim is perfect, or air tight. It is well to have two sizes of emery powder, coarse and fine. Moisten the emery with oil or water when grinding. Place oil or vasaline on plate to prevent air getting under receiver.

[graphic]

Exp. 1. The Hand Glass. Grind the ends of a small lantern globe, then place on plate and exhaust the air. Allow each pupil to experience this 15 pounds downward pressure by placing hand on receiver. Turn the plate sidewise. or invert to show that the air presses equally in all directions. Exp. 2. Bursting Pressure of

Air.

Have a pupil stretch very tightly over the small end of receiver used in Exp. 1 a piece of dental rubber. Exhaust the air quickly and the pressure of the outside air will burst the rubber with a loud report. This rubber may be gotten at any dental office. The dentist will give you waste rubber sufficient for a dozen experiments.

Exp. 3. The Magdeburg Hemispheres.

This famous experiment is beautifully illustrated by making a receiver of a glass tumbler or glass cover from a butter dish or a candy jar. Exhaust the air and have two pupils try to pull the plate and the receiver apart. They are sure to fail. Of course you must remember that the larger the mouth of the receiver the greater the area pressed upon and the greater the effort required to separate the receiver from the plate. You will in all probability have to keep the pump at work to prevent failure from leakage.

Exp. 4. The Mouth as an Air Pump.

Repeat No. 3 using the mouth for

[blocks in formation]

of rubber to end of tube. Exhaust the air from bottle by use of mouth, pinch the rubber tube tightly to prevent air returning to bottle, place tube in water when you will have a good fountain. The amount of water in bottle indicates the percentage of vacuum you produced. Explain carefully the philosophy of the unbalanced pressure of 15 lbs. without, and a lesser pressure within the bottle.

Exp. 6. A Pressure Fountain.

Exp. 7.

The "Lung Tester."

Blow strongly in A when a jet of water will leave B. C is the condensed air above the After blowing

water. remove cork or turn aside the tube A to prevent back-flow of water in your face.

Fig IV.

Reverse the glass tube of No. 5, fill the bottle one-fourth full of water, blow strongly into the jet tube and you will have a pressure fountain the height of which will depend upon your power to condense air with the mouth.

Fig. V

You will have no cause to regret the success of No. 7. It removes conceit from the mind of a smart boy better than can be done in any other way. Arrange jet tube and condensing tube through a large two hole cork using half gallon bottle as shown in figure. The inflowing tube must have much the larger opening. This experiment never fails. Exp. 8. Air Supports Combustion.

Grind a receiver of a half gallon or three quarts capacity. This may be made from a candy jar or by grinding out the bottom of a three quart bottle using first the smooth side of a grindstone, then finish on glass plate with fine emery. Place

lighted candle under receiver and exhaust. Explain.

Exp. 9. Air Supports Life.

Place a live mouse under receiver and exhaust. Better still, place flies under receiver and observe that they cannot fly. The air must be well exhausted however or your experiment will fail. Try an English sparrow under receiver but do not kill the bird. It doesn't matter about the flies. They are plentiful and cheap.

Exp. 10. Air in Wood.

Fasten a block of pine in the bottom of a glass, fill with water, place under receiver and exhaust. Hundreds of bubbles will arise from the wood. Try an egg and note the air bubbles.

Exp. 11. Air in Water.

Place a bottle of water under receiver and exhaust. When the vacuum is good you will see hundreds of bubbles rising through the water. Fishes breathe the air thus dissolved in water. A very interesting experiment is to place a fish in water under receiver. Watch the bubbles leave its mouth. It would soon die for want of air.

(Continued next month.)

Our readers will be sorry to learn that Prof. Mills is, as he expresses it, "Flat on his back with "Grip", and as a result his article on Arithmetic does not appear this month.

THE TEACHING OF DRAWING. At the last session of the Superintendents' Round Table held at Dayton, November 25 and 26, the following questions on the subject of drawing were proposed. One of the leading superintendents of the State suggests that they be republished in this department of the MONTHLY for the consideration of teachers and superintendents in general. If a sufficient number of concise and pointed answers is sent to the editor at an early date a summary of them will be made up and published sometime in the near future. Long drawn-out communications without pith or point cannot be considered.

1- Why is the teaching of drawing so barren of results?

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