"cutting the soap." The soap separates out in the solid form as a curdy
mass, which can be easily separated. Certain soaps are able to absorb a
large quantity of water, and yet appear quite solid, and in purchasing
large quantities of soap it is necessary, therefore, to determine the
amount of water present. This can be easily done by weighing out ten or
twenty grams of the soap, cut in small pieces, into a porcelain dish and
heating over a gas flame, whilst keeping the soap continually stirred,
until a glass held over the dish no longer becomes blurred by escaping
steam. After cooling, the dry soap is weighed, and the loss of weight
represents the amount of moisture. I have known cases where soap
containing about 83 per cent. of water has been sold at the full market
price. Some soaps also contain more alkali than is actually combined
with the fatty acids of the soap, and that excess alkali is injurious in
washing silks and scouring wool, and is also not good for the skin. The
presence of this free or excess alkali can be at once detected by
rubbing a little phenolphthalein solution on to the freshly-cut surface
of a piece of soap; if free alkali be present, a red colour will be
produced.




LECTURE VII

SHELLAC, WOOD SPIRIT, AND THE STIFFENING AND PROOFING PROCESS


_Shellac._--The resin tribe, of which shellac is a member, comprises
vegetable products of a certain degree of similarity. They are mostly
solid, glassy-looking substances insoluble in water, but soluble in