AND CERTAIN METHOD TO DETERMINE THE COMMERCIAL VALUE OF SOAP.

BY DR. ALEXANDER MUeLLER.

In consequence of the ceremonious process by which the fatty acids are
determined in one portion of the soap, and the alkali by the
incineration of another, I consider the following method is not unworthy
of publication, because it appears to afford quicker and more correct
results by reason of the greater simplicity of the manipulation. It is
available principally for soda soaps, which are the most common; but it
may be also employed with corresponding alterations for soaps which have
other bases.

A piece of soap weighing two or three grammes is dissolved in a tared
beaker glass of about 160 cubic centimetres capacity with 80 to 100
cubic centimetres of water, by heat, in a water-bath, and then three or
four times the quantity of diluted sulphuric acid or as much as is
necessary to decompose the soap, added from a burette. When, after
repeated agitation, the fatty acids have separated in a transparent
clear stratum from the aqueous solution, it is allowed to cool, and then
the contents of the beaker glass are placed in a moistened filter, which
has been previously dried at 212 deg. Fahr. and weighed. The contents of the
filter are washed until their acid reaction disappears. In the meanwhile
the beaker glass is placed in a steam-bath, so that, it being already
dry, may support the washed and partly dry filter, which is laid on the
mouth of the glass as if it were in the funnel. The fatty acids soon
pass through the paper, and for the most part flow ultimately to the
bottom of the beaker glass; the increase of weight of which, after
cooling, and the subtraction of the weight of the filter, gives the
quantity of fatty acids present in the soap. A second drying and
weighing is not necessary, if on the cold sides of the interior of the
glass no damp is to be observed, which is occasioned by a trace of water
still present. If the quantity of oxide of iron added to marble the soap
is considerable, it may be easily found by incinerating the filter and
determining the weight of the residue.

The fluid runs from the fatty acids on the filter, which, with the
washings, has been preserved in a sufficiently large beaker glass, is
colored with tincture of litmus, and decomposed with a test alkaline
solution until the blue color appears. The difference of the quantity of
alkali required to neutralize the sulphuric acid, and the quantity o