110 METHOD OP ASCERTAINING- THE QUALITY OP SOAPS. 
dry carbonate of soda. The quantity of pure potash or 
soda may be thus deduced. 
There is no difficulty in ascertaining in the same assay the 
quantity of the fatty substance. For this purpose 10 grms. 
of pure white wax free from water are added to the liquid 
after saturation with sulphuric acid, and the whole heated 
to complete liquefaction ; it is then allowed to cool, and 
when it has become solid, the cake of wax and fatty matter 
which have united is removed and washed, dried and 
weighed ; the augmentation in weight beyond the 10 grms. 
employed will give the weight of the fatty matter. 
The liquid decanted from the solidified wax may after- 
wards be tested to ascertain the purity of the base. 
The solution of the sulphate may also be evaporated, 
and by an examination of its crystalline form, or by means 
of chloride of platinum, it may be ascertained whether the 
base be soda or potash, or a mixture of the two. 
As to the nature of the fatty substance it is ascertained, 
with more or less certainty, by saturating the solution of 
the soap with tartaric acid, collecting the fat acids, and tak- 
ing their point of fusion. It is possible, at least, by this to 
prove the identity or the absence of identity with the sam- 
ple in the soap supplied, for instance whether it is made 
from oil or tallow, &c. The odour developed by the fatty 
acids, at the moment of the decomposition of the soap by 
acids, assisted by heat, will often indicate the nature of the 
fatty substance employed in its fabrication, or that at least of 
which the odour may prevail. 
The soap is proved to contain an excess of fatty matter 
not saponified, by separating the fatty acids by means of hy- 
drochloric acid, washing with hot distilled water, then com- 
bining them with baryta, and thoroughly washing the new 
compound with boiling water. The non-saponified fatty mat- 
ter is easily separated from the barytic soap, by treating the 
mass with boiling alcohol, which dissolves the fatty sub- 
stance. We can moreover assure ourselves that it has no 
