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 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 rilling 

 the aperture of the condenser. For convenience in adjust- 



<J 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 



