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.
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