Fenner's Complete Formulary - Southwest School of Botanical ...

CALCULATING THE SPECIFIC GRAVITY OF SOLIDS.
The druggist is so seldom required to calculate the specific gravity of
solids, that mere mention, only, of the methods will be given here.
Solids heavier than water are first weighed in the ordinary way, and
then, by suspending them to one side of the balance by a fine thread,
are immersed in water and weighed. The ordinary weight divided by the
loss of weight in water gives the specific gravity of the solids.
Solids lighter than water are first weighed, and then attached or tied to
some heavy metal of known weight and specific gravity; the two
substances are then weighed and immersed in water together and the
loss of weight of the lighter substance found by deducting the loss of
weight of the heavy metal, previously found, from the total loss. The
original weight of the lighter substance is then divided by its loss of
weight in water, as shown by the former operation and the result is the
specific gravity of the substance.
Solids soluble in water are first weighed by the balance and then
weighed suspended in some liquid in which they are insoluble, as
Naphtha, Alcohol or Oil. The weight in the liquid subtracted from the
ordinary weight gives the loss of weight; the ordinary weight is divided
by the loss of weight thus obtained, and the quotient multiplied by the
specific gravity of the liquid in which the solid was weighed—this gives
the specific gravity of the solid.
Powdered substances are first weighed, and their weight added to that
of the specific gravity bottle and 1000 grains of water, as described for
calculating the specific gravity of liquids. The powder is then put in the
bottle and enough distilled water at 15.6° C. (60° F.) added to fill it to
Fenner’s Complete Formulary - Part I-II - MISCELLANEOUS FORMULA - Page 15
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