Treatise on Poisons by Sir Robert Christison

1. _Hydrosulphuric acid_ causes a black precipitate, the sulphuret of

lead. This is a test of extreme delicacy; and it acts in whatever state of combination the lead exists, whether fluid or solid. It is preferable to the hydrosulphate of ammonia as a medico-legal test; for, as Fourcroy observed, the hydrosulphate of ammonia acts on many sound wines as if they contained lead,[1223] while hydrosulphuric acid never causes with them a black precipitate, unless they contain either lead or some other metallic impregnation. It must be remembered that many other metallic solutions, such as those of mercury, copper, silver and bismuth, yield a black precipitate with this test.