c. of water.
~Ammonic Sulphide~ may be purchased in the state of a strong solution.
It is yellow, and contains the disulphide, S_{2}Am_{2}. It serves the
same purpose as is obtained by passing a current of sulphuretted
hydrogen through an ammoniacal solution; but has the disadvantage of
loading the solution with sulphur, which is precipitated when the
solution is subsequently acidified. It is useful for dissolving the
lower sulphide of tin (SnS).
~Baric Carbonate~ (BaCO_{3}) is sometimes used for precipitating the
weaker bases. It should be prepared when wanted by precipitating a
solution of baric chloride with ammonic carbonate and washing. The moist
precipitate is used without drying.
~Baric Chloride~, BaCl_{2}.2H_{2}O.--A crystallised salt, soluble in
2-1/2 parts of water. It is used for the detection and separation of
sulphates. Make a 10 per cent. solution.
"~Black Flux.~"--A mixture of finely divided carbon with carbonate of
potash or with carbonates of potash and soda. It is prepared by heating
tartar or "rochelle salt" until no more combustible gas is given off.
One gram will reduce about 2 grams of lead from litharge.
~Borax~, Na_{2}B_{4}O_{7}.10H_{2}O.--It is chiefly used as a flux in dry
assaying, as already described. It is also used in testing before the
blowpipe; many metallic oxides impart a characteristic colour to a bead
of borax in which they have been fused.
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