Art. XLIV.—On the Absorption of Antimony and Arsenic from a Solution of their Oxides in Hydrochloric Acid by Charcoal.

By William Skey, Analyst to the Geological Survey of New Zealand.

[Read before the Wellington Philosophical Society, January 29, 1876.]

Some time back I showed ^* that charcoal, when freshly made or ignited, absorbs, from their aqueous or acid solutions, several substances not before known as being affected in this manner, and I proposed to apply this reaction to the purification of certain of our chemical re-agents from substances difficult or tedious to remove by the processes now in use for this purpose.

Since then I have made further investigations in this direction, and find that antimony and arsenic can be so largely removed from solutions of their oxides or chlorides in moderately strong hydrochloric acid (with a little tartaric acid in the case of antimony) by fresh charcoal, that neither of them can be detected therein by Reinsch's test, although before such process was applied both were abundantly evidenced to the test named.

Thus commercial sulphuric and hydrochloric acids diluted with a little water can be purified from either of these substances by agitating them intermittingly for a short time with fresh charcoal, and then filtering off; application of heat to the mixture expedites this result.

The charcoal used does not appear to give up any portion of either the antimony or arsenic when digested with an aqueous solution of potash, hence I consider it very probable that it would absorb either of these metals from alkaline solutions also. Such charcoal, however, when placed in voltaic contact with pure zinc in hydrochloric acid, evolves antimoniuretted or arseniuretted hydrogen (as the case may be) very perceptibly, and it can be wholly divested of either of these substance, when treated in this manner.

In connection with this evolution of such hydrides from charcoal under the circumstances just stated, I will observe here that sulphur, when