ORIGINAL COMMUNICATIONS. 
CRYSTALLIZATION and the Microscorr. 
By Tuomas Daviszs. 
In no branch of science does the microscope prove more 
useful than in the study of the numerous forms of the 
erystallization of salts. The exceeding minuteness of these 
forms constitutes no difficulty in their study; and where 
their tenuity renders them so transparent as to become 
literally invisible, polarized light generally lays them open 
to observation, with the addition of every beauty that colour 
can bestow. Without this aid, who would have suspected 
the rings and cross of nitre, or the gorgeous appearance 
of salicme? Even more than this may be asserted when 
we remember how many valuable facts there are which 
would still remain unknown without the aid of polarized 
light and the microscope. 
But before the subject is entered into, the question may 
be asked, what is crystallization? This may be briefly 
described as the formation of certain substances in shapes 
according to fixed laws, which shapes are always the same 
except under interfering causes. The most frequent ex- 
amples of crystallization occur when a solution of some salt 
has been made, and the liquid is again driven off by the aid 
of heat. If this process is repeatedly performed, on exami- 
nation the crystals will always be found of the same shape, 
provided that no chemical change has taken place. But it is 
not by solution and evaporation alone that this phenomenon 
is displayed. From other causes crystals are formed, of 
which the three following may be termed the principal : 
lst. Simple evaporation (as above), where water is driven 
off by heat, or where the salt is soluble to a greater extent 
in hot water than cold. A saturated solution being made in 
this case in hot water, a certain portion of the salt becomes 
crystallized on the liquor cooling. 
VOL. IV.—NEW SER. 8 
