PRUSSIAN BLUE is the deep blue color which is so frequently seen on col ton. muslin, and woolen handkerchiefs and dresses. It was discovered in the year 1710 by Diesbach, a color-maker in Berlin, and hence called &Him blue. The mode of its manufacture was published in Britain, by Dr. Woodward, in 1724. It may be prepared is several ways: 1. By the addition of a solution of yellow prussiate of potash (ferrocyamde of potassium) to a solution of sulphate of iron (green vitriol). The blue compound thus produced deepens'in tint when exposed to the air; and where it is required of greater consistence or more body, sonie alum and carbonate of potash are added to the prussiate solution before mixing wilt the iron solution. 2. By mixing solutions of yellow prussiate of potash and perehloride of iron, which yields the variety known as Panay blue. 3. By adding a solution of the red prussiate of potash (ferrocyanide of potassium) to a solution of sulphate of iron, and this mode of preparation gives Turnbull'e blue. The Prussian blue settles to the bottom of the mixing vessels, and may be collected and dried by expo sure to the air, when it is obtained as a blue powder. It heat he applied during the dry
ing, the material cakes, and when cut, exhibits a lustre and hue like copper. Mien alum has been used in its manufacture, the product has a dull earthy fracture. The composition of Prussian blue is that of a ferroeyanideof iron. See CYANOGEN. It is employed by washerwomen, under the name of blue, for neutralizing the yellow tint of cotton and linen clothes; by paper-makers, to color paper; and is-very largely employed! as a pigment in Calico-printing (q.v.) and Dyeing (q.v.). Mintral blue is formed the Prussian blue is precipitated along with asolution of zinc or magnesia, or moist car bonates of zinc or magnesia are added during the precipitation of the color. In the for mation of royal blue, a solution of tin is added, and steam blue is produced on the addi tion of solutions of tartaric' acid and yellow prussiate of potash. The impurities liable to be present in Prussian blue are starch, chalk, and stucco, either of which necessarily decreases the intensity of the blue color, and the utility of the substance.