Treatise on Poisons by Sir Robert Christison

2. _Sulphuretted hydrogen gas_ causes a dark brownish-black precipitate,

the sulphuret of copper. This test is one of very great delicacy; but it is not alone decisive of the presence of copper, since lead, bismuth, mercury, and silver, are similarly affected by it. A method, however, will be presently described, by which the precise nature of the sulphuret may be determined. The alkaline hydrosulphates, for example the hydrosulphate of ammonia, answer equally well with sulphuretted-hydrogen. The solution of the common liver of sulphur throws down, not a black, but a chestnut precipitate.