METHOD OP ASCERTAINING THE QUALITY OP SOAPS. 109 
ART. XXVII.— METHOD OF ASCERTAINING THE QUALI- 
TY OF SOAPS. 
To determine the quantity of water, thin slices are cut 
from the edges and the centre of the bars. A portion is 
then weighed, about 4 or 5 grms. (60 to 75 grs.,) and expos- 
ed in a current of air heated to 212° F., or in an oil-bath, 
until it ceases to lose weight. The dry substance is then 
weighed; the difference between the first and last weighing 
will indicate the quantity of water evaporated. If it be a 
soft soap, it is weighed in a counterpoised shallow capsule. 
In good soap the amount of water varies from 30 to 45 per 
cent., in mottled and soft soaps from 36 to 52 per cent. 
The purity of soap may be ascertained by treating it with 
hot alcohol ; if the soap be white and without admixture, 
the portion remaining undissolved is very minute, and a 
mottled soap of good quality does not leave, when operating 
on 5 grms., more than 5 centigrms., or about 1 per cent. 
If there should be a sensible amount of residue from 
white soap, or more than 1 per cent, from mottled soap, 
some accidental or fraudulent admixture may be suspected, 
silica, alumina, gelatine, &c, the quantity and nature of 
which may be determined by analysis. 
The quantity of alkali contained in the soap is easily de- 
termined by means of the alkalimeter. 
10 grms. in thin slices are taken, for instance, and dissolv- 
ed in 150 grms. of boiling water; and this solution is sa- 
turated with a normal liquor containing in a quart of water 
100 grms. of sulphuric acid, spec. grav. 1-848, or with 1 
atom of water. 
The volume of this liquor required for complete satura* 
tion will indicate the corresponding weight of sulphuric 
acid, which is itself nearly equivalent to an equal weight of 
10* 
