_--If to a water you suspect to be hard from presence of carbonate
of lime or carbonate of iron in solution in carbonic acid, _i.e._ as
bicarbonates, you add some clear lime-water, and a white precipitate is
produced, you have a proof of carbonate of lime--hardness. If the
precipitate is brownish, you may have, also, carbonate of iron. I will
now mention a very delicate test for iron. Such a test would be useful
in confirmation. If a very dilute solution of such iron water be treated
with a drop or two of pure hydrochloric acid, and a drop or so of
permanganate of potash solution or of Condy's fluid, and after that a
few drops of yellow prussiate of potash solution be added, then a blue
colour (Prussian blue), either at once or after standing a few hours,
proves the presence of iron.
_Copper._--Sometimes, as in the neighbourhood of copper mines or of some
copper pyrites deposits, a water may be contaminated with small
quantities of copper. The yellow prussiate once more forms a good test,
but to ensure the absence of free mineral acids, it is first well to add
a little acetate of soda solution.
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