$9* C H E M I 
The operatioft of volatilizing by beat, fucli fubftances 
as are in a dry, folid, and often cryftall'ine ftate, is called 
fublimation. The lublimatory veffels are of glazed 
earthen ware, or earthen cucurbits, with glafs heads, or 
pots of earthen ware, or porcelain, called aludels, ma- 
traffes, &c. Sulphur, arfenic, cinnabar, and many mer¬ 
curial preparations, home vegetable matters, and in par¬ 
ticular camphire and benzoin, are the chief fubftances 
which are raifed in. fublimation. In this procefs, the 
condenfed vapours, which generally aflume.a powdery 
form, are called flowers : fuch are the flowers of brim- 
■ftone, of benjamin', of zink. &c. Solid products obtain¬ 
ed in this way are called fublimates. 
Evaporation is the aCtion of heat upon liquids, in or¬ 
der to diminifli the fluidity and quantity of the refiduum, 
and to obtain the fixed bodies it may hold in folution. 
In this way the water of the fea or fait fprings is driven 
off, and the fait is left. This operation is made in broad 
veffels of earth, glafs, filver, or other metals, according 
to the nature of the liquids under examination. Eva¬ 
poration is performed by an open fire, or with accefs of 
■air, in order that the fluid intended to be driven off may 
be at liberty to expand and be diflipated, and that this 
may be effefted more quickly by virtue of the diflolvent 
•power of the air on fluids in a ftate of vapour. 
Diftillation is a procefs nearly of the fame nature as 
the preceding, but performed in clofed veffels ; which 
are either alembics, or retorts, calculated to feparate the 
volatile from the fixed principles,- by means of heat. Dif¬ 
tillation is improperly diftinguifhed into three kinds, by 
afcent, per afeenfum ; by defeentr, per deccnfuvi ; and lide- 
■vvays, per latus. Thefe diftinCtions, which are but futile, 
feem to have been taken from the form of the veflels. 
Matter in a date of vapour always tends to rife, but dil- 
tiilation by alembics has been called per afeenfum, becaufe 
■the capital being immediately above the body, the va¬ 
pours rife in an obvious manner. The diftillation by 
retorts has been called per latus, becaufe the neck of the 
retorts come out at the fide of the apparatus, though the 
•roof of the retort be higher than its neck, and though 
•the vapours pafs over only after having been condenfed 
by the external cold in the roof, or highefi part of the 
retort. As to the diftillation per defeerifum, it is an un¬ 
skilful and ill-contrived operation, which is no longer 
tifed, becaule its produCts are for the molt part loft, and 
■thole which are obtained are in a foul and imperfect 
Hate. It was performed by placing fome vegetable fub- 
ftance on a cloth extended over the mouth of a glafs vel- 
fel containing fome water ; on this was-laid a metal dilh 
containing live coals. In this way-cloves, and feveral 
“odoriferous matters w.ere in the ancient pharmacy, and 
rfor perfumers’ ufe, diftilled to obtain their effential oil. 
The produCt palled through the linen, and was condenf¬ 
ed by the water ; but the greateft part made its efcape be¬ 
tween the metallic dilh cover and the cloth. A diftinc- 
-tion relating to the manner of heating bodies intended 
'to be diftilled, is much more neceffary to be made than 
■thole we have been (peaking of. The water bath, the 
vapour bath, the land bath, the bath of allies, ccnflft of 
thefe fubftances contained in proper veffels over the fire. 
In thele the diftillatory veffels are plunged, and are by 
that means kept at a more certain and equal heat. The 
jiaked lire is alfo ufed in diftillations, as is alfo the flame 
of a lamp, or of fpirit of wine. 
Rectification is a fecond diftillation, in which fub¬ 
ftances are purified by their moft volatile parts being 
trailed by heat carefully managed. Thus fpirit of .wine, 
ether, &c. are rectified by their feparation from the lets 
-volatile and foreign matter, which altered or debafed 
itheir properties. 
Concentration is the inverfe of rectification, aWt is 
Untended to deprive fixed fluids of the water which 
'weakens them. This operation implies, it is evident, 
.that the matter to be concentrated is heavier than water, 
•and is ufed for-certain acids, particularly the fulphuric, 
•i 
S T R Y. 
phofphoric, and alfo for folutions of alkaline and neu¬ 
tral falts. 
Digeftion is an operation in which fuch matters, as 
are intended to aft flowly on each other, are expofed to 
a flow heat continued for a long time. It is particularly 
ufed in the extraction of luch parts from vegetables as 
are Ibluble in fpirit of wine, or other fluids uled for this 
purpofe. The ancient chemifts held this procefs in great 
eftimation. Though this confidence feems well founded, 
in confideration of the change which, after ftriCt exami¬ 
nation, it is found that moft vegetable and animal fub¬ 
ftances undergo by a too powerful heat, yet it is not 
carried to that entbufiafm which the alchemifts Ihewed 
in their purfuits. Thefe men, with more afliduity and 
labour than their pretended art delerved, made digef- 
tions of many years duration, and believed, by that 
means, that it would be in their power to work a great 
number of miracles. Digeftion is now confined to the 
preparing of tinClures, elixirs, cordials, &c. and it is 
fuccefsfully uled in the extractions of vegetable or ani¬ 
mal principles without alteration. It is likewife ufed to 
advantage in feveral proceffes with minerals 
Infufion is a procefs well known. It conlifts in pour¬ 
ing water of any required degree of temperature on fucli 
fubftances as have a loofe texture, as thin bark, wood in 
lhavings or fmall pieces, leaves, flowers, &c. It is very 
ufeful in feparating the moft loluble parts of thefe, and 
is applied in a great number of chemical operations. 
DecoCtion, or continued ebullition with water, is em¬ 
ployed to feparate fuch parts of bodies as are only foluble 
at this degree of heat. It greatly alters vegetable and 
animal matters, coagulates the lymph, melts the fat and 
refills, hardens fibrous parts ; and is advantageoufiy ufed 
in chemical operations, by fuch as are acquainted with 
its effeCls. 
Lixiviation is the operation of diffolving or extract¬ 
ing, by the help of hot water, the Inline and foluble mat¬ 
ter contained in the allies of plants, or the relidues of 
diftillation, or combuftion, or of coals, or natural earths, 
intended to be analyfed. As, by this operation, halts of 
the kind termed lixivial are generally obtained, it was 
natural to give it the name which it bears: the fynony- 
mous word leffive, is, at prefent, more frequently uled in 
France, than even the term lixiviation. This operation, 
therefore, is nothing more than a folution by the aflift- 
ance of heat, and does not differ from infufion, except 
in the particular application of the latter to vegetable 
and animal matters, while the former is applied to fub¬ 
ftances that have the properties of minerals. 
Such are the different operations performed in clie- 
miftry, by the afliftance of fire.: and as nothing was for¬ 
merly done -without this agent, this fcience was then no 
more than an art, and was called Pyrotechnia. At pre¬ 
fent it is much lei's ufed, in conlequence .of the difeovery 
of more certain methods of analyling natural fubftances. 
The aCtion of folvents, or menftruums, employed with¬ 
out the application of any heat beyond the temperature 
of the air, is fufficient to effect the moft lingular changes, 
and is productive of clear and valuable deductions. This 
method is purfued with luccefs in the examination of falts, 
earth, vegetable matters, &c. Heat is now regarded only 
as an auxiliary agent, by which combinations are for¬ 
warded. As it is employed in different degrees, it would 
be a valuable acquifition if we knew bow to apply it 
with uniform intenfity, A furnace of this kind has long 
been a defideratum among chemifts, and the manipula¬ 
tions of artifts have hitherto been the only guide to the 
chemift; but it is impofiible by this means to have the 
degree of precifion fo much to be defired. The late Dr. 
JBlack. feems to have fucceeded bell in contriving fur¬ 
naces proper to produce a regular and uniform heat, and 
is therefore much recommended. 
As the whole of the praClical part of chemiftry conlifts 
in placing bodies in contaCl with each other, fo that they 
may exert their refpeCtive attractions or powers of com • 
hinatkut 
