Things To Make - Archibald Williams (the reader ebook .TXT) 📗

Run a hole vertically through C and the baseboard for the pivot, which should be 4-1/2 inches long, so as to project 1 inch when driven right home. Take some trouble over getting the holes in L and C quite square to the baseboard, as any inaccuracy will make the lever twist as it moves. To prevent the pivot cutting into the wood, screw to the top of C a brass plate bored to fit the pivot accurately. The strain will then be shared by the screws.

The horns of A should be long enough to allow the outside of the fixed grip to be 2-1/4 inches from the inside of the handle.

The balance is secured first to the lever by a pin driven through the eye of the hook, and then to B by a 3-inch screw passed through the ring. The balance should just not be in tension.

When the apparatus is so far complete, test it by means of a second balance applied to D. Set the scale-marker at zero, and pull on the D balance till, say, 35 lbs. is attained. If the fixed balance shows 7 lbs. on what is meant to be a 5 to 1 ratio, the setting of R relatively to P and Q is correct. If, however, there is a serious discrepancy, it would be worth while making tests with a very strong balance, and establishing a corrected gradation on a paper dial pasted to the face of E.

For twisting tests we need a special handle (see Fig. 164), which is slipped on to the pivot and transmits the twist to L through a pin pressing on the back of the lever. The stirrup is made out of strip iron, bent to shape and drilled near the ends for the grip spindle. To the bottom is screwed and soldered a brass or iron plate, into the underside of which the pin is driven.

[Illustration: FIG. 164.—Handle for twisting test.]

To prevent the handle bending over, solder round the pivot hole 3/4 inch of brass tubing, fitting the pivot closely.

Tests.—Grip tests should be made with each hand separately. The baseboard should lie flat on a table or other convenient support, and be steadied, but not pushed, by the hand not gripping.

Twisting tests may be made inwards with the right hand, and back-handedly with the left. The apparatus is stood on edge, square to the performer, resting on the horns of A and a support near the balance.

Finger tests are made by placing the thumb on the front face of B, and two fingers on the farther side of the lever, one to the left and the other to the right of the tail of the balance.

XXX. LUNG-TESTING APPARATUS.

The capacity of the lungs, and their powers of inspiration and expiration, can be tested by means of easily constructed apparatus which will interest most people who are introduced to it. The reduction of the capabilities of the lungs to figures affords a not unprofitable form of entertainment, as even among adults these figures will be found to vary widely.

Air Volume Measuring.—The air which the lungs deal with is scientifically classified under four heads:

1. Tidal air, which passes into and out of the lungs in natural breathing. About 30 cubic inches in an adult (average).

2. Reserve air, which can be expelled after a normal expiration. About 100 cubic inches.

3. Complemental air, which can be drawn in after a normal inspiration. About 100 cubic inches.

4. Residual air, which cannot be removed from the lungs under any conditions by voluntary effort. About 120 cubic inches.

The first three added together give the vital capacity. This, as an addition sum will show, is very much greater than the volume of air taken in during a normal inspiration.

The simplest method of testing the capacity of an individual pair of lungs is embodied in the apparatus shown in Figs. 165 and 166. A metal box is submerged, bottom upwards, in a tank of somewhat larger dimensions, until the water is level with the bottom inside and out. A counterweight is attached to the smaller box to place it almost in equilibrium, so that if air is blown into the box it will at once begin to rise.

If we make the container 7-1/16 inches square inside, in plan, every inch it rises will represent approximately 50 cubic inches of air blown in; and a height of 7 inches, by allowing for 325 cubic inches, with a minimum immersion of half an inch, should suffice even for unusually capacious lungs. The outside box need not be more than 8 inches all ways.

[Illustration: FIG. 166.—Section of lung-capacity tester.]

Unless you are an expert with the soldering iron, the making of the boxes should be deputed to a professional tinman, who would turn out the pair for quite a small charge. Specify very thin zinc for the air vessel, and have the top edges stiffened so that they may remain straight.

On receiving the boxes, cut a hole 3/4-inch diameter in the centre of the bottom of the air vessel, and solder round it a piece of tubing, A, 1 inch long, on the outside of the box. In the centre of the larger box make a hole large enough to take a tube, E, with an internal diameter of 1/8 inch. This tube is 8 inches long and must be quite straight. Next procure a straight wire, C, that fits the inside of the small tube easily; make an eye at the end, and cut off about 9 inches. Bore a hole for the wire in a metal disc 1 inch across.

[Illustration: FIG. 166.—Perspective view of lung-capacity tester.]

The air container is then placed in the water box and centred by means of wooden wedges driven in lightly at the corners. Push the small tube through its hole in the water box, and thrust the wire—after passing it through the disc and the projection on the air container—into the tube. The tube should reach nearly to the top of the air container, and the wire to the bottom of the water box. Solder the tube to the box, the wire to the disc, and the disc to the container. A little stay, S, will render the tube less liable to bend the bottom of the box. Plug the tube at the bottom.

The wire sliding in the tube will counteract any tendency of the container to tilt over as it rises.

A nozzle, D, for the air tube is soldered into the side of A, as shown.

The counterweight is attached to the container by a piece of fine strong twine which passes over two pulleys, mounted on a crossbar of a frame screwed to the sides of the water box, or to an independent base. The bottom of the central pulley should be eight inches above the top of the container, when that is in its lowest position.

For recording purposes, make a scale of inches and tenths, and the corresponding volumes of air, on the side of the upright next the counterweight. The wire, W, is arranged between counterweight and upright so that an easily sliding plate, P, may be pushed down it by the weight, to act as index.

[Illustration: FIG. 167.—Apparatus for showing lung power.]

Notes.—The pulleys must work easily, to reduce friction, which renders the readings inaccurate. Absolute accuracy is not obtainable by this apparatus, as the rising of the container lowers the water level slightly, and the air has to support part of the weight of the container which was previously borne by the water. But the inaccuracy is so small as to be practically negligible.

A Pressure Recorder.

[Transcribers note: Even with the precautions used in this project, health standards of 2004 would consider any exposure to mercury dangerous. Water could be substituted and the column lengths scaled up by about 13.5.]

If mercury is poured into a vertical tube closed at the bottom, a pressure is exerted on the bottom in the proportion of approximately one pound per square inch for every two inches depth of mercury. Thus, if the column is 30 inches high the bottom pressure is slightly under 15 lbs. per square inch.

This fact is utilized in the pressure recorder shown in Fig. 167, a U-shaped glass tube half filled with mercury. A rubber tube is attached to the bent-over end of one of the legs, so that the effects of blowing or suction may be communicated to the mercury in that leg. Normally the mercury stands level in both tubes at what may be called the zero mark. Any change of level in one leg is accompanied by an equal change in the opposite direction in the other. Therefore, if by blowing the mercury is made to rise an inch in the left leg, the pressure exerted is obviously that required to support a two-inch column of mercury—that is, 1 lb. per sq. inch. This gives a very convenient standard of measurement, as every inch rise above the zero mark indicates 1 lb. of pressure.

CONSTRUCTION.

The mercury tube should be made first. Take a piece of glass tubing 20 inches long, and bend it at a point 9 inches from one end after heating in a spirit flame. The legs should be kept as parallel as possible. Lay the tube, while the heated part is still pliant, on a flat surface, the bend projecting over the edge, So that the two legs shall be in line. When the glass has cooled, bend over two inches of the longer leg to an angle of about 45 degrees.

A standard for the tube is now made out of one-inch wood. Hollow out a bed in which the tube shall lie and be completely protected. To the right of the tube the standard is notched to take a small bottle. The notch should be slightly narrower than the diameter of the bottle, and have its sides hollowed out to fit.

Halfway up the tube draw a zero mark across the standards, and above this a scale of inches in fractions on both sides. Each inch represents 1 lb. pressure.

The cork of the bottle must be pierced with a red-hot wire for two glass tubes, one of which is bent over for the blowing tube. Both tubes should be pointed at the bottle end so that they may enter the cork easily. Make the top of the cork air tight with sealing-wax. The purpose of the bottle is to catch any mercury that might be sucked out of the tube; one does not wish mercurial poisoning to result from the experiments. Also it prevents any saliva entering the mercury tube.

When the latter has been secured to the standard by a couple of slips of tin nailed to the front, connect it up with the bottle, and fill it up to the zero mark with mercury poured in through a small paper funnel.

The open end of the tube should be provided with an inch of tubing. Clips placed on this and on the rubber connection between tube and bottle will prevent the escape of mercury should the apparatus be upset when not in use.

The average blowing pressure of which the lungs are capable is about 1-1/2 lbs. per square inch; inspiration pressure without mouth suction about 1 lb. per square inch; suction pressure 2-1/2 to 3 lbs. per square inch.

Caution.—Don't ask people with weak lungs to try experiments with the apparatus described in this chapter.

XXXI. HOME-MADE HARMONOGRAPHS.

Have you ever heard of the harmonograph? If not, or if at the most you have very hazy ideas as to what it is, let me explain. It is an instrument for recording on paper, or on some other suitable surface, the figures described by two or more pendulums acting in concert.

The simplest form of harmonograph is shown in Fig. 168. Two pendulums are so suspended on points that their respective directions of movement are at right angles to one another—that is, pendulum A can swing only north and south, as it were, and pendulum B only east and west. On the top of B is a platform to carry a card, and on the upper end of A a lever is pivoted so as to be able to swing only vertically upwards and downwards. At its end this lever carries a pen, which when at rest lies on the centre of the card platform.

[Illustration: FIG. 168.—Simple Rectilinear Harmonograph.]

The bob, or weight, of a pendulum can be clamped at any point on