Persian Red Prepared in the Wet Way.

Practical Magazine 23, 1876

(Chemistry applied to the Arts, Manufactures, &c.)

If carbonate of lead is digested with a cold solution of neutral chromate of potassia (one part of the chromate in 50 parts of water) in the proportion of two particles of carbonate of lead to one particle of the chromate, after two days a red crystalline precipitate of basic chromate of lead is formed, of the following composition: 2CO₃Pb + CrO₄K₂ = CrO₄Pb. PbO + CO₃K₂CO₂.

The liquid contains bicarbonate of potassia. If afterwards the whole is boiled, a more basic chromate of lead, of a violet red, and neutral chromate of potassia, is formed, carbonic acid being disengaged at the same time.

The violet precipitate, if treated with 4 per cent. of its weight of sulphuric acid, diluted with 100 parts of water, is changed into a mixture of red chromate and sulphate. To prevent its being changed into chrome yellow by reaction, it is necessary to neutralize the acid liquid exactly by the soda. The red thus obtained is very bright. In place of sulphuric acid azotic acid or acetic acid may be employed.