[Illustration: FIG. 162.—Plan of strength tester.]
[Illustration: FIG. 163.—Grips of strength tester.]
As the pressures on the machine are high, the construction must be
solid throughout. The lever frame, A, and pivot piece, C, should be of
one-inch oak, and the two last be screwed very securely to the
baseboard. The shape of A is shown in Fig. 163. The inside is cut out
with a pad saw, a square notch being formed at the back for the lever
to move in. The handles of an old rubber chest expander come in useful
for the grips. One grip, D, is used entire for attachment to the lever;
while of the other only the wooden part is required, to be mounted on a
1/4-inch steel bar running through the arms of A near the ends of the
horns. If a handle of this kind is not available for D, one may
substitute for it a piece of metal tubing of not less than 1/2-inch
diameter, or a 3/4-inch wooden rod, attached to an eye on the lever by
a wire passing through its centre.
A handle, if used, is joined to the lever by means of a brass plate 3/4
inch wide and a couple of inches long. A hole is bored in the centre
somewhat smaller than the knob to which the rubber was fastened, and
joined up to one long edge by a couple of saw cuts. Two holes for
good-sized screws must also be drilled and countersunk, and a socket
for the knob must be scooped out of the lever. After making screw holes
in the proper positions, pass the shank of the knob through the slot in
the plate, and screw the plate on the lever. This method holds the
handle firmly while allowing it to move freely.
The lever tapers from 1-1/2 inches at the pivot to 5/8 inch at the
balance end. The hole for the pivot—5/16-inch steel bar—should be long
enough to admit a piece of tubing fitting the bar, to diminish
friction, and an important point, be drilled near the handle edge of
the lever, so as to leave plenty of wood to take the strain. The last
remark also applies to the hole for the balance pin at Q.
The balance support, B, and the pivot piece, C, are 2-1/2 and 2-7/16
inches high respectively. 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.