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The arseniuretted hydrogen produced is passed through a tube containing lead acetate paper and soda-lime, and finally through a narrow glass tube, constricted at various points, and heated by a very small flame.

A piece of bibulous paper, moistened with silver nitrate, is held over the mouth of the tube, and if arsenic be present, a grey or black deposit is seen on the paper, due to the silver nitrate being reduced by the arseniuretted hydrogen.

As the arseniuretted hydrogen passes over 652 the heated portion it is decomposed and a black deposit formed.

No case of injury from the inhalation of arseniuretted hydrogen has come under my own personal observation, if we except the one above alluded to.

Dear Sir,—I stated in my letter to Dr. North, if I recollect correctly, that the use of animal food was resumed in consequence of a protracted indisposition brought on, as was supposed, by the inhalation of arseniuretted hydrogen gas.