This substance is likewise precipitated by salts of zinc, mercury, and silver. All these precipitates are pink or purple, very beautiful, and of remarkable brilliancy. They are soluble in alkalies. Iron salts yield no precipitate, nor do lead salts, except in the presence of ammonia, when a blue-violet precipitate is formed. When treated with sulphuretted hydrogen, these precipitates yield purple-red and acid liquids, which undergo change in the air, especially if warm, forming Prussian blue. When these liquids are neutralised with alkali, purple compounds are formed, which are permanent in the air, soluble in water, slightly so in alcohol, and insoluble in ether. Their colouring power is exceptionally great. These pigments will unite with ferrocyanides, and in its preparation such a compound is produced in considerable quantity; it is likewise of a purple colour, and gives a rose-coloured precipitate with acetate of lead. Both alone and in this compound it is very permanent; it resists the action of sulphurous acid, concentrated and boiling alkalies, and dilute acids, but is rapidly destroyed by chlorine and nitric acid. If this pigment could be prepared cheaply enough, it would probably be used with advantage in the arts, on account of its resistance to chemical reagents and light, the variety of its shades, and its brilliancy. It does not colour fibres directly, but can readily be fixed on them from slightly acid solutions, if they are previously mordanted with metallic oxides. BRUNSWICK BLUE.--This pigment is made in pale, medium, and deep shades, and is an extremely useful colour, being very fine, requiring no grinding, thoroughly permanent in light and air, hardly acted upon by acids, but turned brown by alkalies, and liable on standing to separate into two portions--a white and a blue--the latter coming to the surface while the former sinks, and necessitating a thorough stirring of the paint before use. It generally consists simply of barytes, or gypsum, or china clay, coloured by a small percentage of Prussian blue, with or without the addition of a lesser proportion of ultramarine. The barytes or other base is very thoroughly agitated in water, while a solution of green copperas and a solution of yellow prussiate are gradually added without ceasing the agitation. When the incorporation of the ingredients has been completely accomplished, the precipitate is settled, washed, filtered, and dried. Following are a few recipes:-- Pale. (1) 1 cwt. barytes, 1 lb. green copperas, 1 lb. yellow prussiate. Pale. (2) 1 cwt. china clay, 2 lb. green copperas, 2 lb. yellow prussiate. Pale. (3) 1 cwt. gypsum, 1½ lb. green copperas, 1½ lb. yellow prussiate. Medium. (1) 1 cwt. barytes, 3 lb. green copperas, 3 lb. yellow prussiate. Medium. (2) 1 cwt. china clay, 6 lb. green copperas, 6 lb. yellow prussiate. Medium. (3) 1 cwt. gypsum, 4½ lb. green copperas, 4½ lb. yellow prussiate.