CHEMISTRY. 
have tlieir parts separated from each other 
by this treatment. 
When bodies of different kinds are brought 
into contact, tliey produce very little of the 
change called chemical, while they continue 
in the solid state. Mechanical trituration 
will forward their mutual action by multi- 
plying the surfaces of contact ; but still the 
masses continue too large to be moved 
amongst each other by the peculiar attrac- 
tions they may be capable of exerting. It 
has been considered as an axiom, in che- 
mistry that bodies do not act on each other 
unless one or both be in the fluid state ; and 
though this is not strictly and universally 
true, yet it is requisite for almost every 
operation of chemistry that this condition, 
either of dense or of elastic fluidity, should 
obtain. The facility with which tlie parts 
of fluids move amongst each other, is no 
doubt the principal cause of this increased 
effect. 
The practical part of chemistry may be 
therefore said to consist almost entirely in 
separating or changing the order of the 
parts of bodies by heat, or of placing bodies 
in such situations with regard to each otlier 
as that, with the assi, stance of heat, if need- 
ful, to produce fluidity, changes or separa- 
tions of the same kind may take place 
among their parts. The actions of electri- 
city, galvanism, and light, will probably be 
soon combined among the leading resources 
of chemistry. 
No change could take place by this or 
any other treatment, if the attractions of the 
parts of bodies to each other were all per- 
fectly the same. It is manifest from the 
facts, that the attraction between some 
bodies is stronger than between others, 
and from tliis remarkable variety in the 
habitudes of bodies, the attractions of che- 
mistry have been called elective attractions. 
A distinction has been made between 
those processes in which water is present, 
and those in which the requisite fluidity 
is produced by strong heat. The first me- 
thod is called the humid way, and the 
other the dry way. 
Tlie practice of chemistry requires in 
most cases of solid bodies, previous to the 
application of heat, or of one body to ano- 
ther, for the exercise of the attractions, that 
some mechanical means should be taken 
to divide their parts from each other. 
These are, 1, chopping or cutting; 2, rasp- 
ing, filing, or shaving; 3, pulverizing or 
grinding ; 4, granulation, as when shot is 
formed by pouring lead into water, or a 
powder of the metal is obtained by shaking 
it in a box, in the fused state, til! it congeals ; 
5, elutriation, or washing, to separate the 
finer or lighter parts of bodies from the 
coarser or larger, as when earthy matters 
are washed from the heavier metallic ones., 
or when a fine pow'der, such as that of 
poundeH emery, is suspended by agitation 
in water which is decanted off, and then 
set to subside while the coarser particles, 
which settle immediately, are left behind ; 
6, hammering, or forging, as in the making 
of tin foil, or leaf gold, or in the extension 
of other metals whether hot or cold ; 7, la- 
minating, as when the metals are passed 
between steel rollers, or when wax is 
poured upon a wooden cylinder, turned 
round in cold water; and, 8, wire draw'- 
ing, as when the metals are drawn through 
an hole in a plate to make wire, or forced 
through an engine, such as that employed 
for glazier’s lead, &c. 
Bodies are distinguished, with regard to 
heat, into fixed, volatile, and refractory. 
The first can scarcely, if at all, be evapo- 
rated ; the second are easily raised or driven 
off; and the third undergo no change. 
The simple application of heat is distin- 
guished by various terms, according to 
the nature of tlie operation, or of the effects 
produced. These are, 1, roasting, which 
consists in exposing minerals to an open 
fire, to drive off their volatile contents ; 2, 
Calcination is the exposure of a body to 
strong heat, in an open vessel, till it under- 
goes no farther change. This word, which 
was formerly used in a general way, is now 
confined to earths and some of the salts, 
and is indeed seldom used ; 3, oxydation 
is the like process with metallic bodies ; 
4, fusion or melting, is the production of 
the state of dense fluidity ; 5, cementa- 
tion is a process wherein solid bodies of 
different kinds, one or more of them being 
in powder, are exposed to heat in a vessel 
nearly closed, with the intention that the 
more volatile parts of the one may unite 
with the other, or its fixed parts ; 6, eli- 
quation is the exposure of a compound 
body, usually metallic, to heat, sufficient 
to fuse one of its ingredients, which runs 
out and leaves the other solid and porous; 
7, digestion consists in keeping bodies for a 
considerable time immersed in a fluid more 
or less heated, in order to effect some com- 
bination between them ; 8, evaporation is 
the dissipation of a fluid by heat ; 9, con- 
centration consists in diminishing the pro- 
portion of water in any solution of saline 
