UTAH ACADEMY OF SCIENCES 209 
disseminated in small grains and particles through the 
gangue matter. In occurances of this nature the grain 
sizes may be measured and their average size determined 
either by a study of polished sections of the ore or the 
same information may be obtained by the microscopic 
examination of representative thin sections. This latter 
procedure is indicated in the case of the disseminated 
ores, since it permits the determination of the non-metal- 
lic minerals composing the gangue and these minerals 
may have an important bearing on the after treatment 
of the ore. As a matter of fact the study of thin sections 
should constitute a preliminary method of analysis almost 
as essential as that of the study of polished sections. 
It is a recognized fact that all sulphide minerals do 
not respond to like conditions of flotation treatment to 
an equal degree, some of them being much more readily 
floated than others which require the application of 
special methods of treatment together with the use of 
certain combinations of oils and other reagents which 
apparently render them more amenable to treatment and 
increases their recovery. Taking for example a copper 
ore in which the copper exists in the sulphide condition 
and is carried by the three minerals, chalcopyrite, chal- 
cocite, and bornite. Each of these minerals contain cop- 
per in a different amount and it may be desired to ascer- 
tain the relative amounts in which these minerals occur 
in the ores, both from a mineralogical standpoint and also 
from a basis of copper content so represented. It may be 
desired to obtain these data for use in experimental test- 
ing, having for its aim the improvement of the flotation 
practice in use. In addition to the copper sulphides the 
ore may also contain pyrite and it is obvious that the 
application of chemical methods in this instance do not 
offer a direct or satisfactory method of obtaining the 
desired data. Since the questions involved have a direct 
bearing on the physical character of the sulphide minerals 
in the ore visual examination by means of the microscope 
and the use of microscopic methods of analysis appears 
to offer the most satisfactory means to obtain the inform- 
ation required. 
A modification of the Rosiwal (*) method can be 
‘Methods of Petrographic Research, Johannesen pp. 291-2. 
