-The
solution should not give a precipitate with ammonium oxalate solution.
_Carbonates._--The solution should not effervesce on addition of nitric
or hydrochloric acid. _Chlorides._--No appreciable precipitate should
be produced on addition of silver nitrate solution and nitric acid.
_Sulphates._--No appreciable precipitate should be produced on adding
hydrochloric acid and barium chloride. _Iron._--50 c.c. of the solution
should not immediately be coloured blue by 0.5 c.c. of potassium
ferrocyanide solution.

_Soap._--Soap is a salt in the chemical sense, and this leads to a wider
definition of the term "salt" or "saline" compound. Fats and oils, from
which soaps are manufactured, are a kind of _quasi_ salts, composed of a
fatty acid and a chemical constant, if I may use the term, in the shape
of base, namely, glycerin. When these fats and oils, often called
glycerides, are heated with alkali, soda, a true salt of the fatty acid
and soda is formed, and this is the soap, whilst the glycerin remains
behind in the "spent soap lye." Now glycerin is soluble in water
containing dissolved salt (brine), whilst soap is insoluble, though
soluble in pure water. The mixture of soap and glycerin produced from
the fat and soda is therefore treated with brine, a process called
"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,