CraneE.| ~ Prospecting, Mining ana Milling Machinery. 225 
attached to the drill. The heaviest parts are the tripod 
weights, which weigh 100 to 150 pounds each. 
To operate a drill, the power (air or steam) is turned on, 
when the drill has been properly set, and the cylinder is ad- 
vanced toward the face of the rock by the feed screw as the 
drilling proceeds. The machine is simple and can be changed 
from the tripod to the column in a few minutes. 
The column is extensible, and can be placed horizontally 
and vertically as convenience demands. Blocks of wood are 
placed between the enlarged ends or feet of the column and 
the walls, when, by means of the screw in the extensible 
part, the column can be fastened securely between any two 
points desired. The cylinder and its mount can be slipped 
back and forth upon the column, and has also a vertical and 
horizontal movement, which may be employed, if desired. 
‘Two men are generally employed with‘each drill; one to op- 
erate the drill and the other to loosen{the bit when it becomes 
fastened in the hole. The loosening of the bit is accom- 
plished by means of a few strokes‘of a hammer, bar, or hand 
drill, while the power is on. The man who attends :to the 
drill (the driller’s assistant) bales out the hole and helps the 
driller in keeping it straight. 
_ There is a greater range in the practice of placing holes 
when drilling is done by hand than when machines are em- 
ployed. The usual practice with hand drills is to begin at 
that point of the face of drift which looks most favorable, 
while with power drills the center or bottom positions are 
generally chosen. To accomplish this the column is set ver- 
tically in the drift and the drill set at the required height 
above the floor. Several holes are then drilled to one side of 
the center, but so slanted as to almost meet at the ends of the 
completed holes. Other holes drilled between this first row 
and the wall, on the same side of the drift, in positions rang- 
ing from normal with the face of the drift to an angle, the 
reverse of that of the first set of holes, or slanting outward, 
complete the arrangement for one side, which is repeated on 
the opposite side of the drift, but in reverse order. Holes 
drilled according to such a system require the supporting 
column to be set up twice for each round of holes. When 
