118 ELEMENTARY CHEMICAL MICROSCOPY 
the liquid to be examined is contained in a special quartz 
cell Q which in turn is held in position upon the stage in a 
cylindrical brass mounting B. This mounting may be leveled 
or slightly adjusted in height with respect to the condenser by 
means of the screws S. The objective 0 of the microscope 
must be specially corrected for use with the quartz cell cover 
and must have a numerical aperture of less than 0.9. This 
latter requirement is accomplished by introducing into the 
objective a funnel diaphragm. As set up for use, the cardioid 
condenser receives substantially parallel rays from the micro¬ 
scope mirror m. The source of these rays must be some power¬ 
ful radiant, most conveniently an arc lamp R. Parallel rays 
are obtained by means of a plano-convex lens L mounted by 
means of short brass bars r, r, three in number, attached to 
the metal screen E. A glass cell W filled with water acts as a 
cooling trough. A black carboard or metal diaphragm D serves 
to cut down the light beam to the proper size for just filling 
the aperture of the condenser. For convenience in adjust- 
B 
<1 o 
Fig. 58. Cell for holding Liquids for Study with the Cardioid Ultramicroscope. 
ment as to distance and height, microscope, cell and lens are 
placed upon adjustable stands with saddle base resting upon 
an optical bench of triangular section. The screen E is tipped 
at such an angle as to project the rays from R upon the properly 
inclined mirror m, when the latter is at a distance of approxi¬ 
mately 60 centimeters from the lens L. The crater of R should 
be about 8 centimeters from L. 
The liquid to be studied is placed in a quartz cell Q, Fig. 58, 
consisting of a grooved quartz disk and cover. With the cover 
in place the liquid forms a thin film q, the excess of liquid being 
forced into the groove 0. The quartz cell is held in position 
upon the stage of the microscope by means of a brass chamber B 
consisting of a bed-piece into which the cell fits, a funnel-shaped 
