the process named EvaPoraTrion is employed. The 
: € diquor is ex- 
to heat in a vessel of such a form as to present a wi 
face to the atmosphere; the fluid is converted into vapor, and the - 
matter that had beén dissolved is thus obtained in a solid s 
The heat employed in evaporation should always be as moderate 
as possible, as the flavor of the solid residuum is otherwise apt to 
be injured, its composition changed, or part of it carried off with 
the vapour. In many cases, the heat afforded by placing the vessel 
containing the fluid to be evaporated over boiling water is sufficient. 
This forms the water bath. fice 
There are many substances, especially those belonging to : 
of salts, which, when their solutions are evaporated to a ce. 
eoncrete in masses of regular forms, hard and trans ] S 
are termed crystals, and the operation itself crystaLtizaTion. The 
first step in this process is to evaporate part of the fluid till the solu- 
tion while at its boiling point is saturated, or retains in solution the 
largest quantity of the body which at that temperature it can hold 
dissolved. On allowing it to cool, the portion which the high tem- 
perature enabled the fluid to hold in solution, will Separate, and crys- 
tals will be formed; and by successive evaporation, the whole of the 
solid matter may be obtained in the crystalline form. In like man- 
ner, crystals are formed by the slow or spontaneous evaporation 
which takes place when a fluid is exposed to the atmospher , and 
these being formed more slowly, are even harder and more perfect i 
their figure than those obtained by hasty evaporation. s 5 a 
In crystallizing, the figure which the body assumes, is regular and 
peculiar to itself, and hence is established the arrangement of crys- 
tals into prismatic, rhomboidal, and other forms; these, how 
are frequently varied by external circumstances. 8 z 
Water is essential to the formation of crystals, and gives them 
their transparency. The crystals of different bodies contain very 
different quantites of this fluid. It is termed their Water of Crystal- 
lization ; and by whatever means it is expelled, the transparency, 
density, and figure of the crystal is lost. If crystals lose their wa- 
-ter of crystallization on exposure to the air, they are said to efflo- 
resce ; if, on the. contrary, water is absorbed, so that the substanee 
mes moist or fluid, it is said to -deliguesce. Ct ae 
- Crystallization is promoted by the access of the « erie air 
to the fluid, and by affording a nucleus or solid point at which the 
crystallization may commence. Some substances have so strong an 
attraction to the fluid in which they are dissolved, that they do not 
separate in the erystalline form, even when the solution has been 
considerably evaporated. They either remain dissolved, forming a 
Jiquor more or less glutinous ; or if the evaporation be carried toa 
greater extent, they are recovered in the solid form, but destitute of 
any regular figure. Some of these bodies, when dissolvud in water, 
may be made to crystallize by the addition of a-small quantity of 
alcohol, which, by exerting a still stronger attraction to the water, 
7 a8 gum, starch, &c. can by management be made to u 
* 
weakens their combination with it. Other substances soluble im 
