224 Microscopical Examination of Rocks. [April, 
as to allow a further treatment on glass plate C with the fine 
emery C. Due precaution should be employed so as not to grind 
' the section uneven. To avoid this the position of the section 
should frequently be changed in grinding. The section is ready 
as soon as it is thin enough to allow a complete study of its 
texture and its component parts, of which a preliminary examina- 
tion under the microscope will be the best test. 
Process of Covering and Remounting—The section is well 
rinsed and brushed to remove any emery ‘which might have 
remained on the glass or which may be accumulated in the pores 
or fissures of the slice. It is then laid in a vessel with turpentine 
in order to dissolve the excess of Canada balsam around the slice. 
In a few minutes it will be softened enough so as to be easily 
removed by a gentle brushing with turpentine, after which it is 
well washed and then dried with chamois leather. In order to 
protect the section and also to increase its pellucity, it is usually 
imbedded in balsam and covered with a thin glass, the thickness of 
which should not exceed 0.25 mm., to allow the use of a high 
magnifying power. 
Usually the glass slide on which the mineral slice has been 
cemented to grind it thin, becomes partly ground during 
the various operations. It may be replaced with a clean slice on 
which the mineral slide is mounted as already described. 
The separation of the section from the original glass is done 
by gently heating it till the Canada balsam b ftened enoug 
so as to allow the removal of the section by a slow sliding to 4 
vessel with turpentine. The heating should be done very gently, 
otherwise a crust of hard Canada balsam will form around the 
sections, the removal of which by aid of turpentine or any other 
dissolving medium will be most difficult. 
Another method consists in laying the glass with its slice in a 
dish with turpentine and to leave it there till the balsam 'S 
entirely dissolved, after which the slice of rock may be separated 
from its glass without any difficulty. The thin slice is transferred 
to another dish with turpentine and left there till it proves to be 
entirely free of any foreign matter. It is then taken from the vessel 
with the point of a knife, rinsed with alcohol and dried, after- 
wards mounted ona glass which has been warmed, when ue 
slice may be placed upon it with a few drops of Canada balsam. 
‘he whole operation of transferring needs great care, as 
