CrANE.| Prospecting, Mining and Milling Machinery. 229 
working the very hard flint should be about as hard as pos- 
sible, that is, beyond the beginning of the straw color into 
the white of drab, if it may be so called. The temper for 
limestone should be sky blue. , 
The miner must, however, use his own judgment as to 
what is the best temper for tools cutting rocks with hardness 
varying between these two extremes by means of the effect of 
the rock cut upon the drill. If the tool batters or cuts, it 
should be tempered harder—that is, the temper should be set 
nearer the yellow or straw color; if it breaks, it must be 
softer, and the temper should be set nearer the blue. 
Signaling Apparatus. 
The signaling apparatus employed is very simple, consist- 
ing in most cases of a gong, which is operated by a cord reach- 
ing to the foot of the shaft. Steel triangles are often used, 
and, in still rarer cases, an iron lever is made to strike a 
plate of metal. In fact, any means is employed by which a 
sound may be made which is sufficiently loud to attract at- 
tention amid the other noises attendant upon a shaft, mine, 
or mill. 
Top and Concentrating Machinery. 
MILL BUILDINGS. 
The buildings containing the concentrating machinery are 
light, being constructed mainly to protect the men and machin- 
ery from the weather; more substantial mill buildings are 
being erected as the mining industry grows. Up to the past 
year the mill buildings have been built according to one 
plan, namely, a large room containing most of the ma- 
chinery, as jigs, rolls, crushers, etc., and is called the jig 
room, which, together with several smaller rooms, as engine, 
boiler, crusher, storage rooms, and coal bunkers, constitute the 
main part of a mill. The crusher room is nearly always on 
the side of the building opposite the boiler room, and is ele- 
vated from 8 to 30 feet above the floor of the jig room; and 
although the room is called the crusher room, the crusher is 
seldom located within it. The boiler and engine rooms are 
generally a foot or so below the floor of the jig room; 7. e., 
the floor of the jig room is elevated several feet above the 
