MICROSCOPIC OBJECTS. 94 



Fig. 187. Plumose Crystals of Quinidine, x 20. 



Quinidine is an alkaloid or vegetable alkali, found in Peru- 

 vian bark, and usually associated with quinine, which it 

 closely resembles. It is not readily soluble in water, but 

 freely in alcohol. The solution, when evaporated, yields the 

 plumose crystals, the great beauty of which, under polarized 

 light, has caused me to draw the reader's attention to the same. 



The crystals show best when mounted in balsam. 



Fig. 188. Crystals of Salicine, x 12. 



These crystals present the same appearance of rotating 

 crosses as the crystals of boracic acid, mentioned at page 93. 

 The method of preparation is, to evaporate from a hot solu- 

 tion in alcohol, or to fuse a small quantity of the salicine 

 over a gas-jet or spirit-lamp until it dissolves, then to run 

 the semifluid mass over the slide; and generally the disks 

 will appear upon the cooling of the glass. If deposited from 

 a solution, it is often found to be the best plan to confine the 

 drop with a wall of varnish or thick gum previously dried. 

 Other forms of interesting crystals which exhibit the cross 

 are boracic acid, sulphate of cadmium, oxalurate of am- 

 monia, Sec. 



Some of the crystals which exhibit the cross have been 

 drawn in fig. 181. The crystals of salicine are best seen 

 when mounted in balsam. 



