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. A drop or two of the prussiate
solution then gives a brown colour, even if but traces of copper are
present.

_Magnesia._--Suppose lime and magnesia are present. You may first
evaporate to a small bulk, adding a drop of hydrochloric acid if the
liquid becomes muddy. Then add ammonia and ammonium oxalate, when lime
alone is precipitated as the oxalate of lime. Filter through blotting
paper, and to the clear filtrate add some phosphate of soda solution. A
second precipitation proves the presence of magnesia.

_Sulphates._--A solution of barium chloride and dilute hydrochloric acid
gives a white turbidity.

_Chlorides._--A solution of silver nitrate and nitric acid gives a white
curdy precipitate.