PHARMACY 
air may escape From them, and then invert- 
ing them with their mouths downwards. 
For filling them with convenience, a trough 
or cistern is commonly used. This should 
either be hollowed out of a solid block of 
wood or marble ; or, if it be constructed of 
w'ood simply, be well painted or lined with 
lead or tinned copper. Its size may vary 
■very much; but it must contain a sufiicient 
depth of fluid to cover the largest transverse 
diameter of the vessels to be filled in it. 
At one end or side, there should be a shelf 
for holding the vessels after they are filled. 
This shelf should be placed about an inch 
and a half below the surface of the fluid, 
and should be perforated with several holes, 
forming the apices of corresponding conical 
excavations on the lower side, through 
which, as through inverted funnels, gaseous 
fluids may be more easily introduced into 
the vessels placed over them. In general 
the vessels used with a mercurial apparatus 
should be stronger and smaller than those 
for a water- cistern, and we must have a 
variety of glass and elastic tubes for convey- 
ing the gases from the vessels in which they 
are formed to the funnels under the shelf. 
The repeated distillation of any fluid is 
denominated rectification. When distilla- 
tion renders the fluid stronger, or abstracts 
water from it, it is termed dephlegmation. 
When a fluid is distilled off from any sub- 
stance, it is called abstraction ; and if the 
product be redistilled from the same sub- 
stance, or a fresh quantity of the same sub- 
stance, it is denominated cohobation. 
The difference between distillation and 
sublimation is only in the form of the pro- 
duct. When it is compact, it is termed a 
sublimate ; when loose and spongy, it for- 
merly had the appellation of flowers. Sub- 
limation is sometimes performed in a cru- 
cible, and the vapours are condensed in a 
paper cone, or in another crucible inverted 
over it ; sometimes in the lower part of a 
glass flask, cucurbit, or phial, and the con- 
densation is effected in the upper part or 
capital, and sometimes in a retort with a 
very short and wide neck, to which a coni- 
cal receiver is fitted. The heat is most 
commonly applied through the medium of a 
sand-bath; and the degree of heat, and the 
depth to which the vessel is inserted in 
it, are regtilated by the nature of the sub- 
limation. 
Congelation is the reduction of a fluid to 
a solid form, in consequence of the abstrac- 
tion of caloric. The means employed for 
abstracting the caloric, are the evaporation 
of volatile fluids, the solution of solids, ami 
the contact of cold bodies. 
Coagulation is the conversion of a fluid 
into a solid of greater or less consistence, 
merely in consequence of a new arrange- 
ment of its particles, as during the process 
there is no separation of caloric or any 
other substance. The means of producing 
coagulation are, increase of temperature, 
and the addition of certain substances, as 
acids and rennets. 
Chemical Combination, is the intimate 
union of the particles of at least two hetero- 
geneous bodies. It is the effect resulting 
from the exertion of the attraction of afli- 
nity, and is therefore subjected to all the 
laws of affinity. 
To produce the chemical union of any 
two or more bodies, it is necessary, that 
they possess an affinity for each other ; that 
their particles come into actual contact ; 
that the strength of the affinity be greater 
than any counteracting causes which may 
be present. 
The principal counteracting causes are, 
the attraction of aggregation ; and affinities 
for other substances. The means to be em- 
ployed for overcoming the action of other 
affinities, will be treated of under Decom- 
position. The attraction of aggregation is 
overcome by means of mechanical division ; 
or the action of caloric. 
Combination is facilitated by increasing 
the points of actual contact, by the means 
of mechanical agitation ; by condensation 
and compression ; and the processes em- 
ployed for producing combination may be 
considered, with regard to the nature of the 
substances combined ; and to the nature of 
the compound produced. Gases combine 
with gases, and dissolve fluids or solids, or 
are absorbed by them. Fluids are dissolved 
in gases, or absorb them; they combine 
with fluids, and dissolve solids, or are ren- 
dered solid by them. Solids are dissolved 
in fluids and in gases, or absorb gases, and 
solidify fluids. 
The combination of gases with each 
other, in some instances, takes place when 
simply mixed together: thus nitrous aud 
oxygen gases combine as soon as they come 
into contact ; in other instances, it is neces- 
sary to elevate their temperature to a de- 
gree sufficient for their inflammation, either 
by means of the electric spark, or the con- 
tact of an ignited body, as in the combina- 
tion of oxygen gas with hydrogen or nitro- 
gen gas. 
When gases combine with each other 
