A mixture of chrome yellow and Prussian blue. [See also Chrome Oxide, further hack.] Barth's Green. A mixture of Prussian blue and yellow lake. Ultramarine, Factitious. Take 70 parts of silica, or pure siliceous sand, in fine powder; 240 parts of recrys-tallized alum, calcined; 144 parts of sulphur; 48 parts of finely powdered charcoal; 240 parts of dry carbonate of soda. These are mixed together with the greatest care till the mixture appears of uniform colour under a powerful magnifier, and the mixture exposed to a moderate red heat in a closely covered crucible for an hour and a half. Wash the product with boiling water, Mix the powder with its own weight of sulphur and 1 1/2 its weight of dried carbonate of soda, and burn as before; heat it again with sulphur and carbonate of soda, and wash it till the filtered fluid no longer colours acetate of lead. If a sample of the dried powder becomes blue when burnt with sulphur, it is ready for the last operation. Spread over a cast-iron plate a layer of sulphur a line in thickness, and over it an equal layer of the dried powder after having passed it through a gauze sieve. Heat the plate so as to burn away the sulphur at the lowest possible temperature. Reduce the pigment to powder, and repeat the burning with sulphur and pulverization till the colour is perfect.

White Lead is carbonate of lead prepared by various processes. Zinc White is oxide of zinc, prepared by combustion. Oxychloride of Zinc is also used. Antimony White is oxide of antimony.