THE ANALYST. 113 NOTES ON AN IMPURITY IN OXIDE OF ZINC. BY W. W. STODDART, F.C.S., &c. Read before the British Pharmaczutical Conferelzoo at Plymouth. A FEW weeks ago I had a sample of oxide of zinc sent to me for analysis. It was bought for mixing with white lead as a paint, but on being ground was found to be nearly useless. It monld not readily combine and form a homogeneous mass, as ueual, nor would it give the I n fact it was so unsatisfactory an article that i t was laid aside and another used in its stead, Some objection was raised to its being returned which caused the firm to have it examined, and the cause of failure ascertained.I have brought the subject before your notice, not on account of the peculiar impurity, but because it has a pharmaceutical interest, for it answers well to all the pharmacopaial tests for pure oxide of zinc, and yet it is impure to the extent of nearly ten per cent.The sample was nearly white with a very slight buff tint. Like the pure oxide it became a strong yellow when heated, regaining its former whiteness when cold. It was perfectly and easily dissolved in an excess of carbonate of ammonia, and the alkaline hydrates.From the alkaline solution a white precipitate was produced by a sulphide of ammonium. It dissolved without effervescence in dilute nitric acid, and was so little affected by chloride of barium that after standing for several minutes, the milkiness was so slight as to require a close scrutiny for its recognition. If, however, the solution in nitric or hydrochloric acid be made in a flask, a strong odour and copious evolution of sulphurous acid gas becomes very evident.A few grains were placed in dilute hydrochloric acid with a small piece of pure zinc when sulphuretted hydrogen was evolved, and speedily became evident with the help of a bit of lead paper. The addition of chlorine water produced a distinct precipitate of sulphate with chloride of barium.The use of nitroprusside gave a red colour with a little of the solution to which a little soda and acetic acid had been added. An analysis showed that the sample was composed of oxide and sulphite of zinc in the following proportions :- body ” required, Oxide of zinc . . . . . . . . . . . . . . . 90.87 Sulphite of zinc . . . . . . . . . . . . . . . 9.13 Sulphate of zinc, a very slight trace. 100*00 The trace of‘ sulphate was so small that it was probably due to oxidation of the sulphite. The cause of the presence of sulphite of zinc is not quite apparent, but the sample came from a continental house, and was very likely manufactured from a sulphide of zinc in some rapid and imperfect manner, which had partially oxidized some of the sdphide, and produced the impure product of which complaint had been made. The appearance of the sample suggested a process by hcat rather than by precipitation.