832 University Geological Survey of Kansas. 
THEORY OF ORE CONCENTRATION. 
Concentration may be effected with little or no sizing, as 
in the English-American method, or with close sizing, ac- 
cording to the continental method. The former method is 
the more closely adhered to in the Galena district. 
The three fundamental operations constituting ore con- 
centration are: Reduction, sizing, and sorting. 
Reduction. 
Reduction is accomplished by means of crushers and rolls. 
THE BLAKEK CRUSHER. 
The Blake crusher and its modifications are the forms used, 
and do the preliminary crushing, with the exception of a cer- 
tain amount of sledge work done on the larger masses of ore 
and gangue brought to the crusher room. The Blake crusher 
is well adapted to the crushing of large sizes, as the maximum 
power is applied at the top of the jaw. The power then di- 
minishes with the size of the material crushed as it passes. 
through the crusher. 
ROLLS. 
The rolls receive the partially crushed material and com- 
plete the reduction. They furnish an excellent form of re- 
duction machinery, as they are inexpensive and give fairly 
uniform results, while the wearing surface is small. 
The size of the roll should vary somewhat with the size of 
the material crushed, but this is rarely done; rather, the 
pressure holding the rollers together is increased. This is. 
probably the reason why so many shells are broken. Theo- 
retically, the size is limited by the coefficient of friction of 
rolls and mineral, but it varies with the shape and character 
of material crushed, also the degree of hardness of the iron 
or metal forming the shells of the roll, and, finally, the speed 
or rate of driving. 
The capacity of rolls varies with the diameter, width of 
face, the distance between rollers, and the speed. There: 
are, however, certain limiting conditions, such as size and. 
