POLARIZED LIGHT. 115 



Very beautiful results may be obtained by a 

 mixture of two or more salts. Mr. Davies, in the 

 Quarterly Microscopical Journal, Vol. II., N.S., 

 gives the following directions for crystallizing the 

 double sulphate of copper and magnesia. Make 

 nearly a saturated solution of the two salts, place 

 a drop on a slide and dry rapidly, allowing the 

 slide to become hot enough to fuse the salt, 

 which will now appear as an amorphous film on 

 the slide. On slowly cooling, the salt will absorb 

 moisture from the surrounding air, and crystalli- 

 zation will commence from various points, assum- 

 ing the appearance of flowers. As soon as these 

 " flowers " are perfected the slide should be 

 slightly warmed and a little of pure Canada balsam 

 dropped upon it, and covered with the usual thin 

 glass cover. 



Sugar requires a somewhat different treatment 

 to any of the crystals previously described, and 

 the tyro's first attempts will probably result in 

 disappointment. The best for the purpose is the 

 white " stone sugar." Dissolve this in water, 

 using enough to form a thick syrup ; spread a 

 drop on a cover, drying it quickly over a spirit- 

 lamp y when dry place it in a damp cellar or 

 cupboard. In the course of twenty-four hours 

 crystallization will have taken place. The cover 

 should now be mounted in balsam. 



Passing from the inorganic to organic we pro- 

 ceed to give a few hints on the preparation of 

 specimens from vegetable and animal kingdoms. 



The following are a few of the objects from the 

 former which the student will have little difficulty 

 in obtaining : 



Potato starch. 

 Tous les mois ditto. 



