Disconnect the apparatus, and wash the cylinder, first with
cold water, then with alcohol. Dry by placing in the water oven for two
or three minutes. Cool and weigh: the increase in weight gives the
amount of metallic mercury.
It must be remembered that copper will precipitate mercury without the
aid of the battery; but in this case copper will go into solution with a
consequent loss in the weight of the cylinder: this must be avoided by
connecting the battery before immersing the electrodes in the assay
solution. The electrolysed solution should be treated with an excess of
ammonia, when a blue coloration will indicate copper, in which case the
electrolysis is unsatisfactory. With a little care this need not happen.
Gold cylinders may preferably be used instead of copper; but on platinum
the deposit of mercury is grey and non-adherent, so that it cannot be
washed and weighed.
VOLUMETRIC METHODS.
Several methods have been devised: for the details of these the student
is referred to Sutton's "Handbook of Volumetric Analysis."
QUESTIONS.
1. The specific gravity of mercury is 13.596. What volume would 8 grams
occupy?
2. If 3.169 grams of cinnabar gave 2.718 grams of mercury, what would be
the percentage of the metal in the ore?
3. Pour solution of mercuric chloride on mercury and explain what
happens.
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