CRYSTALLIZATION, 
This is a very extensive genus, and consists 
of 268 species. See PI. N. H. figs. 151, 152. 
CRYPTOGAMIA, one of Linnaeus’s 
classes of plants, the organs of fructification 
of which are either concealed within the fruit 
itself, or so minute as to escape observation. 
It embraces 4 orders; lilices, musci, algie, 
and fungi, which see. 
CRYPTOSTOMUM, a genus of the pen- 
tandria class and order. The calyx is five- 
cleft; tube of corolla inserted into the throat 
of the calyx ; borders live-cleft ; nect. five- 
toothed ; berry, seeds scarred. There is 
one species, a shrub of Guiana. 
CRYSTAL, in natural history, the name 
of a very large class of fossils, har'd, pellucid, 
and naturally colourless. 
CRY STALLIZATION. The word crys- 
tal originally signified ice; but it was af- 
terwards applied by the antients to crystal- 
lized silica, or rock crystal ; because, as 
Pliny informs us, they considered that body 
as nothing else than water congealed by tire 
action of cold. Chemists afterwards applied 
the word to all transparent bodies of a regu- 
lar shape ; and at present it is employed to de- 
note in general the regular figures which bo- 
dies assume when their particles have full 
liberty to combine according to the laws of 
cohesion. These regular bodies occur very 
frequently in the mineral kingdom, and have 
long attracted attention on account of their 
great beauty and regularity. By far the 
greater number of the salts assume a crystal- 
line form ; and as these substances are 
mostly soluble in water, we have it in our 
power to give the regular shape of crystals 
m some degree at pleasure. 
All the substances with which we are ac- 
quainted may be divided into solid, liquid, and 
gaseous. Crystals are obviously confined to 
the first set, the fluidity of the two last 
rendering them incapable of retaining a re- 
gular form; but many of them may be made 
to assume a solid state, and in that case they 
usually crystallize. Most solid bodies either 
occur in the state of crystals, or are capable 
of being made to assume that form. Now it 
has long been observed by chemists and mine- 
ralogists, that there is a particular form which 
every individual substance always affects 
when it crystallizes: this indeed is considered 
•as one of the best marks for distinguishing one 
substance from another. Thus common salt is 
observed to assume the shape of a cube ; and 
alum that of an octahedron, consisting of two 
four-sided pyramids, applied base to base. 
Saltpetre affects the form of a six-sided prism ; 
sulphat of magnesia, that of a four-sided 
prism ; and carbonat offline is often found in the 
stateof a rhomboid. Not that every individual 
substance always uniformly crystallizes in 
the same form ;’ for this is liable to consider- 
able variations, according to the circum- 
stances of the case; but there are a certain 
number of forms peculiar to every substance ; 
and the crystals of that substance, in every 
case, adopt one or other of these forms, and 
no other ; and thus common salt, when crys- 
tallized, has always either the figure of a cube 
or octahedron, or some figure reducible to 
these. 
As the particles of bodies must be at li- 
berty to move before they crystallize, it is ob- 
vious that we cannot reduce any bodies to 
the state of crystals, except those which we 
-are able to make fluid. Now there are two ways 
of rendering bodies fluid, namely, solution in a 
liquid, and f usion by heat. These of course 
are the only methods of forming crystals in 
our power. 
Solution is the common method of crystal- 
lizing salts. They are dissolved in water: 
the water is slowly evaporated ; the saline par- 
ticles gradually approach each other, com- 
bine together, and form small crystals ; 
which become constantly larger by the ad- 
dition of other particles, till at last they fall 
by their gravity to the bottom of the ves- 
sel. Or a saturated solution being prepared 
in hot water, it is set by to cool. On the es- 
cape of the caloric, by which, in fact, the 
solution was in great part accomplished, the 
salt crystallizes. Such salts commonly form 
in groups, attached to the sides or bottom of 
the vessel, or depending from a pellicle. 
They usually contain more water of crystal- 
lization than the former class. 
There are many substances, however, nei- 
ther soluble in water nor other liquids, which, 
notwithstanding, are capable of assuming a 
crystalline form. This is the case with the 
metals, with glass, and some other bodies. 
The method employed to crystallize them is 
fusion, which is a solution by means of caloric 
alone. By this method particles are sepa- 
rated from one another; and if the cooling 
proceeds gradually, they are at, liberty to 
arrange themselves in regular crystals. 
To obtain large artificial crystals of a re- 
gular shape requires considerable address and 
much patient attention. This curious branch of 
practical chemistry has been much improved 
by Mr. Leblanc ; who has not only succeed- 
ed in obtaining regular crystals of almost 
any size at pleasure, but has made many in- 
teresting observations on »rystallization in 
general. His method is as follows: The 
salt to be crystallized is dissolved in water, 
and evaporated to such a consistency that it 
shall crystallize on cooling. Set it by, and 
when quite cold pour the liquid part from 
the mass of crystals at the bottom, and put it 
into a flat-bottomed vessel. Solitary crys- 
tals form at some distance from each other, 
and these may be observed gradually increas- 
ing. Pick out the most regular of these, 
and put them into a flat-bottomed vessel at 
some distance from each other, and pour 
over them a quantity of liquid obtained in the 
same way by evaporating a solution of the salt 
till it crystallizes on cooling. Alter the po- 
sition of every crystal once at least every 
day with a glass rod, that all the faces may be 
alternately exposed to the action of the liquid : 
for the face on which the crystal rests never 
receives any increment. By this process the 
crystals gradually increase in size. When 
they have acquired such a magnitude that 
their form can easily be distinguished, the 
most regular are to be chosen, or those having 
the exact shape which we wish to obtain ; and 
each of them is to be put separately in a ves- 
sel filled with a portion of the same liquid, and 
turned in the same manner several times a 
day. By this treatment they may be obtained 
of almost any size we think proper. After 
the crystal lias continued in the liquid for a 
certain time, the quantity of salt held in solu- 
tion becomes so much diminished, that the 
liquid begins to act upon the crystal and re- 
dissolves it. 1 his action is first perceptible on 
the angles and edges of the crystal. They 
become blunted, 'and gradually loso their 
4.6 1 
shape altogether. Whenever this begins to 
be perceived, the liquid must be poured oil', 
and a portion of new liquid put in its place ; 
otherwise the crystal is infallibly destroyed. 
Mr. Leblanc has observed, that this singular 
change begins first at the surface of the 
liquid, and extends gradually to the bot- 
tom ; so that a crystal, if large,’ may be often 
perceived in a state of increase at its lower 
end, while it is disappearing at its upper ex- 
tremity. Mr. Leblanc even affirms that sa- 
line solutions almost always increase in den- 
sity according to their depth from the sur- 
face. 
It has been observed, that those salts which 
crystallize upon cooling, do not assume a 
crystalline form so readily if they are al- 
lowed to cool inclose vessels. If a saturated 
solution of sulphat of soda, for instance, in hot 
water, in put into a phial, corked up closely, 
and allowed to cool without being moved, no 
crystals are formed at all; but the moment 
the glass is opened the salt crystallizes with, 
such rapidity that the whole of the solution 
in a manner becomes solid. It seems then 
that the caloric, or rather the last portions of 
it, cannot be carried oil’ without the air or 
the atmospherical pressure in the liquid. 
Not only salts, but water itself, which com- 
monly crystallizes at 32°, maybe made to exhi- 
bit the same phenomenon : it may be cooled 
much lower than 32 degrees without freezing. 
This, as Dr. Black lias completely proved, 
depends entirely upon the retention of ca- 
loric. 
The phenomena of crystallization seem to 
have attracted but little of the attention of the 
antient philosophers. Their theory, indeed, 
that the elements of bodies possess certain re- 
gular geometrical figures, may have been 
suggested by these phenomena; but we are 
ignorant of their having made any attempt to 
explain them. The schoolmen ascribed the 
regular figure of crystals to their substantial 
forms, without giving themselves much trou- 
ble about explaining the meaning of the term. 
This notion was attacked by Boyle; who 
proved tthat crystals are formed by the mere 
aggregation of particles. But it still remained 
to explain why that aggregation took place ; 
and why the particles United in such a man- 
ner as to form regular figures. 
The aggregation is evidently the conse- 
quence of attraction, but to explain the cause 
of the regular figures is a more difficult task, 
Newton lias remarked, that the particles of 
bodies, while in a stateof solution, are arran- 
ged in the solvent in regular order and at regu- 
lar distances; the consequence of which must 
be, that when the force of cohesion becomes 
sufficiently strong to separate them from the 
solvent, they will naturally combine in groups, 
composed of thee particles which are nearest 
each other. Now all the particles of the 
same body must be supposed to have the 
same figure: and the combination of a deter- 
minate number of similar bodies must pro- 
duce similar figures. Hauy has made it ex- 
ceedingly probable that these integrant par- 
ticles always combine in the same body in 
the same way ; that is to say, that the same 
faces, or the same edges, always attach 
themselves together ; but that these differ 
in different crystals. This can scarcely 
be accounted for, without supposing that 
the particles of bodies are endowed with 
a certain polarity, which makes them attract 
