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 Imay term) imediwm, 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 salt 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, Tartrate 
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 not 
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. Someof 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 absolute 
alcohol, and use it warm; by dropping a small quantity 
from a warm pipette on to a warm slide a film will spread 
