COMMON OBJECTS WORTH EXAMINING. 291 



may be made to crystallize by preparing a strong solu- 

 tion and allowing it to slowly evaporate, and the forma- 

 tion of the crystals may be watched with the micro- 

 scope. A small drop is placed on the slip and allowed 

 to evaporate while on the stage. Sugar crystals can be 

 prepared in this way. Common salt is very easily made 

 to crystallize, and scarcely anything can be more beau- 

 tiful than salt crystals viewed as opaque objects with a 

 strong light reflected on and from them. The follow- 

 ing are also noteworthy :* 



Tartaric Acid. Make a strong solution and place a 

 large drop on the slide. Evaporate with a gentle heat 

 by holding the slide several inches above the top of the 

 lamp chimney. 



Gallic Acid. A. small drop of a strong solution in al- 

 cohol should be allowed to evaporate very slowly. 



Pyrogallic Acid. A strong cold solution in water 

 forms long needle-shaped crystals, " but if a very minute 

 shower of some insoluble foreign substance be allowed 

 to fall upon the solution when on the slide the effect is 

 grand each minute speck forming a nucleus around 

 which the needle-shaped crystals gather, forming, if ex- 

 amined with a selenite slide, so resplendent an object 

 that no words of mine can adequately describe it." * 



Chlorate of Potash. Make a strong solution in hot 

 water and allow a small drop to spread evenly over the 

 cell and evaporate slowly. To form dendritic or tree- 



* American Monthly Microscopical Journal, August, 1883. 



