Treatise on Poisons by Sir Robert Christison

2. _Chromate of potass_, both in the state of proto-chromate and

bichromate, causes a fine gamboge-yellow precipitate, the chromate of lead. For the characteristic action of this reagent, it is desirable that the suspected liquid be neutral. It forms with solutions of the sulphate of copper a precipitate nearly of the same colour as the chromate of lead.