Antimony (III) salts in the presence of tartrate ions may be quantitatively precipitated with a large excess of aqueous pyrogallol as the dense antimony pyrogallate. The method facilitates a simple separation from arsenic; the latter element may be determined in the filtrate from the precipitation of antimony by direct treatment with hydrogen sulphide.
The solution should contain antimony (III) (0.1-0.2 g). Add a slight excess over the calculated quantity of potassium sodium tartrate to avoid the formation of basic salts upon dilution. Dissolve approximately five times the theoretical quantity of pure pyrogallol in lOOmL of air-free water, add this all at once to the antimony solution, and dilute to 250 mL. After 30-60 seconds
the clear mixture becomes turbid, and then a dense, cloudy precipitate forms which separates out rapidly. Allow to stand for 2 hours, filter through a weighed sintered glass or porcelain filtering crucible, wash several times with cold water to remove the excess of pyrogallol (50 mL is usually sufficient), dry at 100-105 °C to steady weight. To confirm that no pyrogallol remains wash again with cold water, dry at 100-105 °C, and weigh; repeat the operation until the weight is constant. Weigh as Sb(C6H5O3).
It should be pointed out that the titrimetric methods described for the determination of antimony are to be preferred to the gravimetric methods as they are simpler, more rapid, and quite as accurate.