114 PREPARATION AND MOUNTING 



temperature during crystallization the character of the 

 crystals is affected. If the fused salt is very hot, the crystals 

 run in straight lines from a common centre. If the heat is 

 (what I may term) medium, the crystals show concentric 

 waves of very decided form. If the slide is cool, the crystals, 

 still concentric, are exceedingly minute. The most beautiful 

 crystals for the microscopist are those formed at a tem- 

 perature betwixt the second and third above mentioned, as 

 the minute and wavy forms are then combined, and long 

 feathery crystals are the result. As this method requires 

 some little practice, many crystallize the s.alt in a simpler 

 manner, which I will give ; but the variations obtainable 

 by fusion give that mode the precedence. Dissolve a few 

 grains of santonine in a drachm of chloroform, and drop the 

 solution upon a glass slide. Allow the liquid to evaporate, 

 and beautiful crystals will be the result. Mount as above. 



In fear of being somewhat uninteresting to part of my 

 readers, I feel as though I should not be fulfilling my desire 

 of giving every information, if I omitted to show another 

 method of crystallization, which a novice would cast away 

 as a failure before he had completed his experiment. Tartrata 

 of soda, made by neutralizing a strong solution of tartaric 

 acid by the addition of carbonate of soda, is spread in solu- 

 tion over a glass slide, and must be then warmed, but net 

 boiled. It must now be laid in a dry place, protected from 

 all chance of dust. In time from one or two days to as 

 many weeks some of the slides will prove beautiful objects, 

 showing the cross form surrounded by rays. Some of these 

 slides never crystallize, though I can find no reason for this, 

 and even the application of heat to these calls out no decided 

 form. 



Hippuric acid will be found most interesting to those who 

 are fond of beautiful polariscopic effects, inasmuch as this 

 salt is capable of giving an astounding variety in the forms 

 of its crystals. Make a saturated solution in absolate 

 alcohol, and use it warm ; by dropping a small quantity 

 from a warm pipette on to a warm slide a film will spread 



