CONVICT LABOR FOR ROAD WORK. 83 
pump method. Those who favor this method claim as an additional 
advantage the fact that the water is not stored in a closed tank or in 
contact with stale air. On the other hand, the equipment necessary 
is more expensive than that required for the operation of the hydro- 
pneumatic tank method, and the mechanism of the pneumatic pump 
is somewhat delicate and demands careful attention to keep it in good 
running order. In particular, the pump must be protected from the 
action of sand or grit in the water. 
PUMPS. 
There are two general types of pumps, namely, suction -lift pumps 
and force pumps. The former depend for their action on the creation 
of a partial vacuum in the pump cy Under, which permits the water 
in the pump to rise above the water in the well. The maximum 
practical suction lift is about 20 feet, though it varies somewhat 
with the elevation above sea level, the greater the elevation the 
smaller the suction lift. This means that the pump cylinder which 
raises the water by suction in lift pumps should never be more than 
20 feet above the water level in the well or other source. In force 
pumps the water is raised mechanically and the height to which the 
water can be raised is not limited as in the case of the suction pumps. 
Pumps of this type are necessary for use in connection with elevated- 
tank or hydropneumatic systems, and, unless a special air pump or 
compressor be used, it is necessary that a combination air-and-water 
force pump be employed for the hydropneumatic systems, especially 
in pumping from deep wells. 
Frequently the two types of pumps are combined, the water being 
raised partly by suction and partly by force. This is accomplished 
either by the use of two cylinders, one for each of the operations, or 
by a combined suction and force cylinder. 
Pumps are manufactured suitable for operation with any kind of 
power — hand, gasoline, steam, or electric. The most suitable form of 
power for the use of convict camps is that of the gasoline engine. 
For the purposes of camps of ordinary size from 2--J to 3 horsepower 
is all that is required, and a gasoline engine of such rating will not 
only pump all the water necessary but will furnish sufficient power 
to run a clothes-washing machine or other small machinery which may 
be useful around the camp. The horsepower necessary for pumping 
purposes in any case may be estimated by the following method: 
Divide the number of gallons which it is desired to pump per 
minute by 7.48 (the number of gallons in a cubic foot), to determine 
the number of cubic feet of water to be pumped per minute. Multi- 
ply the number of cubic feet by 62.5 (the weight in pounds of a cubic 
foot of water) to get the weight of the water to be pumped per min- 
ute. Multiply this weight by the total lift in feet. The total lift 
will be equal to the vertical distance from the surface of the water 
