EXCAVATING MACHINERY USED IN LAND DRAINAGE. 5 
The following formula? for determining the latent heat of steam 
at various gage pressures is based on experiments made by M. Reg- 
—nault: 
L (nearly) =965.7—0.7 (¢—212°) 
in which ¢ is the steam temperature in degrees Fahrenheit to be ob- 
tained from the preceding table. 
It is convenient to remember that 1 horsepower per hour is equiva- 
lent to 2,545 British thermal units. Assuming 13,000 British thermal 
units in a pound of coal, the latter is equivalent to 5 horsepower- 
hours. From 18 to 20 pounds of bituminous coal per hour is burned 
with natural draft on 1 square foot of fire grate. 
Very frequently too small a boiler is used on a machine, and the 
boiler must be worked to its utmost capacity to furnish the necessary 
amount of steam. This results in great waste of fuel, which could 
easily be avoided by using a boiler of the proper capacity. On a 
certain 1-yard steam-operated drag-line excavator with a 50-foot 
boom the coal consumption per cubic yard was found to be 10 pounds. 
The boiler was replaced later with another of 35 per cent greater 
capacity, for which the fuel consumption was only shghtly over 7 
pounds per cubic yard. 
ELECTRIC POWER. 
The United States Reclamation Service used electrically operated 
drag-line excavators with 14-yard buckets and 50-foot booms, 
mounted on caterpillars, in the excavation of 3,800,000 cubic yards. 
The ditches varied from 5 to 10 feet in base width, had 14 to 1 and 2 
to 1 side slopes, and averaged 10 feet deep. The excavation per mile 
was approximately 40,000 cubic yards. Eighty-horsepower motors 
were used to move the machines while 40-horsepower motors operated 
the swinging drums. The average amount of current used was 0.88 
kw. h. per cubic yard, including all line and transformer losses. In 
sandy-loam soil only 0.4 kw. h. per cubic yard was required. The 
transmission lines consisted of three No. 4 copper wires on 30-foot 
poles carrying current at 4,000 volts. This was transformed to 440 
volts at the machines. The lines were torn down and rebuilt as the 
work progressed. 
2 Kent's Mechanical Engineer’s Pocketbook, 7th ed., p. 462. 
