254. ANNUAL REPORT 
dried are charged at the stack end and discharged, hot, at the furnace 
end. The capacity of such a machine is from 5 to Io tons per hour, de- 
pending on the condition of the material and the amount of moisture con- 
tained by it. It requires from 4 to 6 horsepower for operation. Owing to 
the fact that this machine discharges the dried material when still hot and 
the gases leave the machine far from saturation it is not the most economi- 
cal type of dryer. Other systems, like the Cummer dryer and others, 
make better use of the heat, but at the same time are more troublesome to 
operate. The dryer shown by the accompanying illustration is a simple 
and, mechanically, an efficient machine, though not the most economical 
type. It is, however, to be preferred to any complicated system in which 
the heat efficiency is counteracted by mechanical difficulties. 
ROUGH CRUSHING MACHINES. 
The dry materials require three kinds of preparing machinery: 
1. Rough crushing machines, 
2. Intermediate grinding machines, 
3. Fine grinding machines. 
These three operations must be clearly kept in mind, as they cannot 
be carried on successfully at one and the same time. 
Of the rough grinding machines two types are employed, known gen- 
erally as the jaw and spindle crusher respectively. In addition another 
type is employed, as far as the writer knows, only in one instance, namely 
the roll crusher. 
Jaw Crusher.—Under the type of jaw crusher we understand a 
number of machines, which though they differ in regard to the move- 
ment of the jaw, or in the number of jaws employed, yet employ 
the one general principle. Thus, we know the Dodge breaker, the Bu- 
chanan, the Duplex breaker, the Forester, the Kron, the Sturtevant and 
others. The Blake crusher is considered typical. Its action is simply 
the opening and closing of steel-faced iron jaws, moved by toggles which 
are set in motion by a vertical eccentric motion. A seven inch by ten inch 
Blake crusher has a movement at the mouth of 0.78 inch, at the throat 
of 0.25 inch, and makes 275 revolutions per minute. As a piece of rock 
is seized by the jaw, it is gradually crushed to a smaller and smaller size 
and worked down towards the throat, the width of which governs the 
size to which the rock is broken. The fixed and the swing jaw plates are 
often made of the hardest. steel obtainable, chrome or manganese steel ; 
if these are not used, chilled iron is found to be the cheapest. In work of 
this sort the most essential requirement is, of course, that the machine 
be amply strong enough for the strains it has to withstand, even if this 
should be accomplished at the cost of some of the capacity. They should 
be able to take the largest lump and reduce it without the necessity of 
breaking up with a sledge. The cost of crushing with a jaw crusher has 
