itself is found in California and Nevada, U.S.A., and also in Peru,
Ceylon, China, Persia, and Thibet. The commercial product is obtained
from the native borax (known as "tincal") by dissolving in water and
allowing the solution to crystallise. The Peruvian borax sometimes
contains nitre. For testing the purity of refined borax the following
simple tests will usually suffice. A solution of the borax is made
containing 1 part of borax to 50 parts of water, and small portions of
the solution are tested as follows: _Heavy metals_ (_lead_, _copper_,
etc.).--On passing sulphuretted hydrogen into the solution, no
coloration or precipitate should be produced. _Calcium Salts._--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