PHARMACY. 
from saline fluids, concentration ; and from 
viscid fluids, inspissation ; or it may be 
total and produce exsiccation. Concentra- 
tion is employed to lessen the quantity of 
diluting fluids, which is called dephlegma- 
tion ; or as a preliminary step to crystalli- 
zation. Inspissation is almost confined to 
animal and vegetable substances; and as 
these are apt to be partially decomposed by 
heat, or to become empyreumatic, it should 
always be performed, especially towards 
the end of the process, in a water or vapour 
bath. Exsiccation is here taken in a very 
limited sense ; for the terra is also with 
propriety used to express the drying of ve- 
getables by a gentle heat, the efflorescence 
of salts, and the abstraction of moisture from 
mixtures of insoluble powders with water, 
by means of chalk-stones, or powdered 
chalk pressed into a smooth mass. At pre- 
sent, we limit its meaning to the total ex- 
pulsion of moisture from any body by 
means of caloric. The exsiccation of com- 
pound oxides should always be performed 
in the w’ater bath. Salts are deprived of their 
water of crystallization by exposing them 
to the action of heat in a glass vessel or iron 
ladle. Sometimes they first dissolve in their 
water of crystallization, or undergo what is 
called the watery fusion, and are after- 
wards converted into a dry mass by its total 
expulsion ; as in the calcination of borax or 
burning of alum. When exsiccation is at- 
tended with a crackling noise, and splitting 
of the salt, as in muriate of soda, it is 
termed decrepitation, and is performed by 
throwing into a heated iron vessel, small 
quantities of the salt at a time, covering it 
up, and waiting until the decrepitation be 
over, before a fresh quantity is thrown in. 
Exsiccation is performed on saline bodies, 
to render them more acrid or pulverulent, 
or to prepare them for chemical operations. 
Animal and vegetable substances are ex- 
siccated to give them a solid form, and to 
prevent their fermentation. 
Condensation is the reverse of expansion, 
and is produced either by mechanical 
pressure forcing out the caloric in a sensible 
form, as water is squeezed out of a sponge, 
or, by the chemical abstraction of caloric, 
which is followed by an approximation of 
the particles of the substance. This fatter 
kind alone is the object of our investigation 
at present. In this way we may be sup- 
posed to condense substances existing na- 
turally as gases or vapours ; or substances, 
naturally solid or fluid, converted into va- 
pours by adventitious circumstances. The 
VOL, V. 
former instance is almost supposititious ; for 
we are not able, by any diminution of tem- 
perature, to reduce the permanently elastic 
fluids, to a fluid or solid state. The latter 
instance is always preceded by vaporization, 
and comprehends those operations in which 
tlie substances vaporized are condensed in 
proper vessels. 
When the product is a fluid, it is termed 
distillation ; when solid, sublimation. Dis- 
tillation is said to be performed, xM, humU 
dH, when fluids are the subjects of the ope- 
ration. Fid siccd, when solids are subject- 
ed to the operation, and the fluid product 
arises from decomposition, and a new ar- 
rangement of the constituent principles. 
The objects of distillation are, to separate 
more volatile fluids from less volatile fluids 
or solids. To promote the union of ditfer- 
ent substances ; and to generate new pro- 
ducts by the action of fire. 
In all distillations, the heat applied should 
not be greater than what is necessary for 
the formation of the vapour, and even to 
this degree it should be gradually raised. 
The vessels also in which the distillation is 
performed should never be filled above 
one-half, and sometimes not above one- 
fourth, lest the substance contained in them 
should boil over. 
As distillation is a combination of evapo- 
ration and condensation, tiie apparatus con- 
sists of two principal parts : the vessels in 
which the vapours are formed ; and tliose 
in which they are condensed. The vessels 
employed for both purposes are very va- 
rious in their shapes, according to the man- 
ner in which theoperation is conducted. The 
first difierence depends on the direction of 
the vapour after its formation. It either 
descends, ascends, or passes oflf by the side, 
constituting a distillation per descensum, per 
ascensum, or per latus. 
Ill the distillation per descensum, a perfo- 
rated plate of tinned iron, or other mate- 
rials, is fixed within any convenient vessel, 
so as to leave a space beneath it. On this 
the subject of the operation is laid, and 
over it is placed another plate, accurately 
closing the mouth of the vessel, and suffi- 
ciently strong to support the fuel : thus the 
heat is applied from above, and the vapour 
is forced to descend into the inferior cavitv, 
where it is condensed. In this way the oil 
of cloves is prepared, and on the same prin- 
ciples tar is manufactured, and mercury 
and zinc are separated from their ores. 
In the distillation per ascensum, the va- 
pour is allowed to arise to some height, 
