PHARMACY, 
from the useless ; the modes of intermixing 
them. 
Weights and Pleasures. The quantities 
of substances employed as medihines are 
determined with the greatest accuracy by 
weighing. The scales should balance with 
the utmost precision, and turn with tlie ut' 
most facility. Balances should be defended 
as much as possible from acid and other 
corrosive vapours, and not be unnecessarily 
suspended, as their delicacy of decision is 
hereby much impaired ; and to guard against 
this last evil in another way, they slionld 
never be over loaded. 
The want of an uniformity of weights 
and measures which is felt in every coun- 
tty, and in every branch of trade and com- 
merce, is of peculiar inconvenience in phar- 
macy. All our college pharmacopoeias 
command the use of troy weight; yet the 
wholesale druggists in every instance, except- 
ing where a very small portion of an article 
is bought by grains, scruples, or drachms, 
sell by ayoirdupoise weight ; and' there is 
reason to fear that, both amongst apothe- 
caries and druggists, most of the pharma- 
ceutic compositions are prepared by this 
last division ; in consequence of which it is 
impossible for the physician to know the 
exact strength of the dose he prescribes, 
and if he do, he cannot often obtain it in 
the proper proportions of its respective in- 
gredients. The difficulty is still increased 
by a promiscuous use of weights and mea- 
sures, in determining the quantities of fluids, 
on which account, though the London col- 
lege still authorises both for distinct pur- 
poses, the colleges of Edinburgh and Dub- 
lin have rejected measures altogether. 
For measuring fluids, the graduated glass 
Pleasures are always to be preferred : they 
should be of different sizes, according to the 
quantities they are intended to measure. 
Elastic fluids are also measured in glass 
tubes, graduated by inches and their deci- 
mals. 
Specific gravity is the weight of a deter- 
Diinate bulk of any body. For a standard 
of comparison distilled water has been as- 
sumed as unity. The specific gravity of 
solids is ascertained by comparing the 
weight of the body in the air with its weight 
when suspended in vvater. The quotient 
obtained by dividing its weight in air by 
the difference between its weight in air and 
its weight in water, is its specific gravity. 
The specific gravity of fluids may be ascer- 
tained by comparing the loss of weight of a 
solid body, such as a piece of crj-stal, when 
immersed in distilled lyater, with its loss 
when immersed in the fluid we wish tp exa- 
mine ; by dividing its loss of weight in the 
fluid by its loss of weight in the water, the 
quotient is the specific gravity of the fluid ; 
or a small phial, containing a known weight 
of distilled water, may be filled with the 
fluid to bp examined and weighed, and by 
dividing the weight of the fluid by the 
weight of the water, the specific gravity is 
ascertained. 
Although these are the only general prin- 
ciples by which specific gravities are ascer- 
tained, yet as the result is always influenced 
by the state of the thermometer and baro- 
meter at the time of the experiments, and 
as the manipulation is a work of great nicety, 
various ingenious instruments have been 
contrived to render the process and calcu- 
lation easy. Of all these, the gravimeter of 
Morveau seems to deserve the preference. 
It would be of material consequence, to 
science and the arts, if specific gravities 
were always indicated by the numerical 
term expressing their relation to the specific 
gravity of distilled water. This, however, 
is unfortunately not the case. The excise, 
officers in this country collect the duties 
paid by spiritous liquors, by estimating the 
proportion which they contain of a standard 
spirit, about 0.933 in specific gravity, which 
they call hydrometer proof, and they ex- 
press the relation which spirits of a different 
strength have to the standard spirit by say- 
ing that they are above or under hydrometer 
proof. Thus one to six, or one in seven 
below hydrometer proof means that it is 
equal in strength to a mixture of six parts 
pf proof spirit with one of water. 
The only other mode of expressing specific 
gravities which it is necessary to notice, is 
that of Baume’s areometer, as it is often 
used in the writings of the French chemists, 
and is little understood in this country. For 
substances heavier than water he assumes 
the specific gravity pf distilled water as zero, 
and graduates the stem of his instrument 
downwards, each degree being supposed 
by him to express the number of parts of 
muriate of soda contained in a given solu- 
tion, which however is not at all the case. 
For substances lighter than water the tube 
is graduated upwards, and this zero is af- 
forded by a solution of 10 of salt in 90 wa- 
ter. 
Mechanical Division. By this process 
substances are reduced to a form better 
