Arsenic is usually estimated either in the form of magnesium pyroarsenate or as arsenic sulphide.
For the pyroarsenate method it is necessary that the arsenic should be in the arsenic condition, if necessary this can be effected by heating with nitric acid; the acid solution is then mixed with "magnesia mixture" and made strongly alkaline by the addition of ammonia.
From the weight of magnesium pyroarsenate obtained the weight of arsenic can be calculated.
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