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.
_Test for Lead in Drinking Water._--I will, lastly, give you a test that
will be useful in your own homes to detect minute quantities of lead in
water running through lead pipes. Place a large quantity of the water in
a glass on a piece of white paper, and add a solution of sulphuretted
hydrogen and let stand for some time.
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