fi. Matlet-—Temperature attainable by Rock-crushing. 265 
not time for the surrounding surfaces of the cold stone to carry 
off the heat evolved by conduction, though the dissipation of 
disappears. The temperature at the crushing-point is greater 
as the work done in a unit of time and upon a given weight of 
the material is greater. That the temperature capable of being 
thus produced approaches that of the fusing-point of steel, is 
of a gun-lock by the flint. In the case of small masses of rock, 
evident from the phenomenon of a spark struck from the steel 
such as the 13-inch cubes of the author’s experiments, crushed 
between two opposite surfaces of steel, the actual temperature 
of the crushed particles can never be found to reach that due 
to the work of crushing; for the heat of relatively small mass 
of the crushed cube in close contact with far larger masses of 
cold steel of high conductivity is carried off almost as fast as 
it is evolved ; and as the total amount of heat evolved from the 
crushing of such a cube of the hardest rock experimented upon 
by the author (namely, number 12, Table I, Phil. Trans., part 1, 
1873, p. 186) could raise its own mass only through 217°, if the 
temperature of fusion of the rock may be taken at 2000°, it is 
obvious that such a cube could not be fused by the work of 
crushing alone, even though all the heat due to the crushing 
work remained in the cube, none being dissipated to surround- 
ing objects. Brite 
In the case of a cube such as this losing heat by dissipation, 
the temperature of the crushed mass depends upon the time in 
which the work of crushing is done. In the author's experi- 
ments the crushing of each cube in column 12 occupied a mean 
time somewhat greater than that in which a heavy body could 
fall freely through a space of 0-09 foot (No. 12, Table L é c., col. 
19)—that is, 0-075 of a second; for more rapidly than that the 
crushing surfaces could not approach each other. If, however, 
the conditions had been such that but 7th the above time were 
expended in the crushing, then a proportionately less quantity 
