210 TRANSACTIONS OF THE 
applied to the case under consideration and the infor- 
mation gained from this mechanical analysis, if properly 
conducted, should be sufficiently accurate to be used as a 
basis for conducting the proposed experimental work. 
The Rosiwal method is by no means new and has been 
used by petrographers and others for making mechanical 
analyses of the rock constituents in thin sections and in 
the determination of the relative amounts of coarse 
gravel, sand, and cement in concrete. Briefly stated it 
consists of the measurement or estimation of the respec- 
tive areas of the constituents in the material being studied 
and reducing these figures to terms of 100 which is desig- 
nated as the relative volume percentages of the com- 
ponents as they occur in the areas studied. Multiplying 
these volume percentages by the specific gravities of the 
respective constituents and converting the results into 
terms of 100 gives the relative weights of the constituents 
which is the information required. In order to apply this 
method of mechanical analysis to the study of crushed 
sulphide material or products obtained by screen sizing 
or concentration, it is first necessary to briquette the 
crushed material with sealing wax. The briquette is 
ground and polished in the same manner as an ordinary 
ore specimen and can be examined and studied under 
the microscope and when thus prepared the application 
of various microscopic methods of manipulation to 
crushed sulphide grains is no more difficult than their 
application to solid uncrushed material. 
A detailed discussion of the uses of the microscope 
in ore dressing is beyond the scope of this paper which 
is intended to treat the subject in a general manner only, 
but the emphasis placed on the necessity for a thorough 
understanding of the physical characteristics of the ores 
and the minerals composing them, together with the 
examples given, serve to illustrate its usefulness in this 
field. It may be stated that those engaged in ore dres- 
sing and concentration both from a research standpoint 
and in practice can ill afford to ignore the microscope 
and that the intelligent application of microscopic 
methods in these fields will prove to be a profitable 
investment. 
