CONVICT LABOR FOR ROAD WORK. 81 
The following table gives commercial sizes of pneumatic tanks: * 
Table 11. — Commercial sizes of pneumatic tanks. 
Diam- 
eter. 
Length. 
Weight. 
Volume. 
Diam- 
eter. 
Length. 
Weight. 
Volume. 
Inches. 
Feet. 
Pounds. 
Gallons. 
Inches. 
Feet. 
Pounds. 
Gallons. 
24 
6 
445 
140 
42 
10 
1,650 
720 
24 
8 
560 
195 
42 
12 
1,900 
865 
24 
10 
675 
245 
42 
14 
2,200 
1,000 
30 
6 
560 
220 
42 
16 
2,400 
1,150 
30 
8 
700 
295 
48 
10 
2,066 
1,000 
30 
10 
870 
365 
48 
12 
2,320 
1,130 
30 
12 
900 
440 
48 
14 
2,610 
1,300 
36 
6 
750 
315 
48 
16 
2,900 
1,500 
36 
8 
900 
420 
48 
18 
3,600 
1,700 
36 
10 
1,050 
525 
48 
20 
3,950 
1,880 
36 
12 
1,200 
630 
48 
24 
4,650 
2,260 
42 
8 
1,450 
575 
60 
20 
5,900 
2,940 
As stated above, the water capacity of the tanks given in Table 11 
will be not greater than three-fourths of the volume of the tank. 
Therefore, for the camp of 40 convicts, assumed above, for which a 
daily supply of 1,800 gallons is necessary, it is evident that a tank 48 
inches in diameter and 14 feet long would be required and it would be 
necessary to pump up this tank twice a day, starting with an initial 
air pressure of at least 11 pounds. 
Pneumatic tanks usually are constructed to withstand safely a 
pressure of 100 pounds per square inch. 
THE PNEUMATIC-PUMP METHOD. 
By the pneumatic-pump method the water is delivered direct from 
the source. As it is not stored in a tank, storage capacity of other 
form must be provided, either a special reservoir or a sufficiently 
large dug well. The necessary apparatus consists of a small gasoline 
engine, an air compressor, an air-tight steel pressure tank, and a pneu- 
matic pump. The operation of the method is as follows: The gaso- 
line engine supplies power to run the air compressor which pumps the 
air in the tank up to any desired pressure. From this reservoir air 
under pressure is supplied to the pneumatic pump which is immersed 
in the water at its source in the well, lake, or brook. The pump con- 
sists of two small metallic chambers; when a faucet is opened these 
fill with water automatically and discharge alternately, owing to the 
alternate application of the air pressure from the tank to the surface 
of the water in each, and a continuous supply of fresh water is thus 
forced through the pipes. 
Plate III shows a front and side view of a pneumatic pump and 
the arrangement of a pneumatic-pump system. 
Each pump requires an air-pressure reducer, shut-off and release 
cocks, and pressure gauge. The air-pressure reducer is necessary to 
reduce the high pressure carried in the tank to the uniform low pres- 
1 Bulletin No. 57, U. S. Department of Agriculture. 
