134 



THE ART OF PROJECTING. 



Starch, 



Tartaric Acid, 

 Urea, 

 Human hair, 



Petals of flowers, as of the 



Geranium, 

 Scales of Fishes. 



Fig. 1 01 represents 

 the appearance of 

 starch grains of the 

 potato, as seen in 

 common light with 



Fig. wi. Fig. io2. the microscope, and 



Fig. 102, the same seen by polarized light. 



The following method of preparing double salts for 

 examination with polarized light is given by Mr. Davies 

 in the " Quarterly Journal of Microscopic Science " : 



" To a nearly saturated solution of sulphate of cop- 

 per and sulphate of magnesia add a drop on the glass 

 slide, and dry quickly. To effect this, heat the slide so 

 as to fuse the salts in its water of crystallization, and 

 there remains an amorphous film on the hot glass. 

 Put the slide aside and allow it to cool slowly. It will 

 gradually absorb a certain amount of moisture from 

 the air, and begin to throw out crystals. If now 

 placed in the microscope, numerous points will be seen 

 to start out here and there. The starting-points may 

 be produced at pleasure by touching a film with a 

 fine needle point so as to admit of a slight amount of 

 moisture being absorbed by the mass of the salt " 



A slide of salicine crystals makes a splendid object 

 for such projection, and should be in every collection. 

 Make a saturated solution of the crystals in distilled 

 water, and place a drop carefully upon a slide that has 

 been carefully cleaned. Evaporate over a lamp until 

 it is dried to an amorphous mass. Upon cooling, a 



