(4) The process adopted by Murdoch, in which a solution of antimony chloride (prepared by dissolving black sulphide of antimony in hydrochloric acid) is acted on by a current of sulphuretted hydrogen gas, has disadvantages in the apparatus necessary, in the limited range of tints which can be produced, and in the almost certain presence of free sulphur in the finished pigment. Antimony vermilion forms an exceedingly useful pigment, which can be prepared in every shade of red, from orange to red-brown. It is produced in the condition of a very fine powder, requiring no grinding, and mixes readily with water or oil, especially the latter, and moreover does not interfere with the drying of the oil. It possesses great covering powers, and can be made at a low price. It undergoes no change in strong light and impure air, and is insoluble in water, alcohol, essential oils, weak acids, ammonia, and alkaline carbonates; but it is destroyed by high temperatures, strong acids, and caustic alkalies. It cannot be mixed with other pigments which are intolerant of sulphur, nor with alkaline vehicles. When pure, it should consist of nothing but antimony sulphide and a little water; the presence of iron or lead indicates adulteration. BARYTA RED.--An orange red may be prepared, according to Wagner, in the form of a sulpho-antimonite of barium, by calcining in a clay or graphite crucible at red heat for several hours a mixture of 2 parts of finely powdered barytes, 1 part of native antimony sulphide, and 1 part of powdered charcoal. The calcined mass is not removed until the crucible is quite cold, as it is liable to undergo combustion. When cold, it is boiled in water and filtered. The residue, containing some undecomposed sulphate and sulphide of barium, is utilised in the next batch. The pale-yellow filtrate is treated with dilute sulphuric acid, by which sulphuretted hydrogen is driven off, and an orange precipitate is thrown down. This is collected, washed on a filter, and dried, constituting the pigment. CASSIUS PURPLE.--This costly pigment is a stannate of protoxide of gold, much used in painting on porcelain and for miniatures. It is the precipitate which is thrown down when solutions of gold and tin chlorides are mixed under proper conditions, according to one of the following methods:--