PHARMACY. 
there is always a considerable diminution 
of bulk, and not unfrequently they are con- 
densed into a liquid or solid form. Hydro- 
gen and oxygen gases form water ; muriatic 
acid and ammonia gases form solid muriate 
of ammonia. But when the combination is 
effected by ignition, a violent expansion, 
which endangers the bursting of the ves- 
sels, previouly takes place, in consequence 
of the increase of temperature. 
Solution is the diminution of aggregation 
in any solid or fluid substance, in conse- 
quence of its entering into chemical combi- 
nation. The substance, whether solid or 
fluid, whose aggregation is lessened, is term- 
ed the solvend; and the substance, by 
whose agency the solution is effected, is of- 
ten called the menstruum or solvent. So- 
lution is said to be performed riii humidd, 
when the natural form of the solvent is 
fluid ; but when the agency of heat is ne- 
cessary to give the solvent its ^nid form, 
the solution is said to be performed vid 
siccd. The dissolving power o^ each men- 
struum is limited, and is determinate with 
regard to each solvend. The solubility of 
bodies is also limited and determinate with 
regard to each menstruum. 
When any menstruum has dissolved the 
greatest possible quantity of any solvend, it 
is said to be saturated with it. But, in 
some cases, althougli saturated with one 
substance, it is still capable of dissolving 
others. Thus a saturated solution of mu- 
riate of soda will dissolve a certain quan- 
tity of nitrate of potash, and after that a 
portion of muriate of ammonia. 
The dissolving power of solvents, and 
consequently the solubility of solvends, are 
generally increased by increase of tempera- 
ture : and conversely, this power is dimi- 
nished by diminution of temperature; so 
that, from a saturated solution, a separation 
of a portion of the solvend generally takes 
place on any reduction of temperature. 
This property becomes extremely useful id 
many chemical operations, especially in 
crystallization. 
Particular terms have been applied to 
particular cases of solution. 
The solution of a fluid in tlie atmosphere 
is termed spontaneous evaporation. It is 
promoted by exposing a large surface, by 
frequently renewing the air in contact with 
the surface, and by increase of temperature. 
Some solids have so strong an affinity for 
water, that tliey attract it from the atmo- 
sphere in sufficient quantity to dissolve 
them ; these are said to deliquesce ; others, 
on the contrary, retain their water of crys- 
tallization with so weak a force, that the 
atmospliere attracts it from them, so that 
they crumble into powder. These are said 
to effloresce. Both operations are promoted 
by exposing large surfaces, and by a cur- 
rent of air ; but the latter is facilitated by 
a warm, dry air, and the former by a cold, 
humid atmosphere. 
Solution is also employed to separate sub- 
stances, (for example, saline bodies), which 
arh soluble in tlie menstruum, from others 
which are not. When our object is to ob- 
tain the soluble substance in a state of pu- 
rity, the operation is termed lixiviation, and 
as small a quantity of the menstnnira as is 
possible is used. Wlien, however, it is em- 
ployed to free an insoluble substance from 
soluble impurities, it is termed edulcoration, 
which is best performed by using a very 
large quantity of the menstruum. 
Organic products being generally com- 
posed of heterogeneous substances, are. only 
partially soluble in the different menstrua. 
To the solution of any of these substances, 
while the others remain midissolved, the 
term extraction is Applied ; and when, by 
evaporation, the substance extracted is re- 
duced to a solid form, it is termed an ex- 
tract, which is hard or soft, watery or spi- 
ritous, according to tlie degree of con- 
sistency it acquires, and the nature of the 
menstruum employed. 
Infusion is employed to extract the vir- 
tues of aromatic and volatile substances, 
which would be dissipated by decoction, 
and destroyed by maceration, and to sepa- 
rate substances of easy solution from others 
which are less soluble. The process con- 
sists in pouring upon the substance to be 
infused, placed in a proper vessel, the men- 
struum, either hot or cold, according to the 
direction, covering it tip, agitating it fre- 
quently, and, after a due time, straining or 
decanting off the liquor, which is now term- 
ed the infusion. 
Maceration differs from infusion, in be- 
ing continued for a longer time, and can 
only be employed for substances wliich do 
not easily ferment or spoil. 
Digestionj on the other hand, differs 
from maceration only in the activity of the 
menstruum being promoted by a gentle de- 
gree of heat. It is commonly performed in 
a glass matrass, which should only be filled 
one-third, and covered with a piece of wet 
bladder, pierced witli one or more small 
