To each lime vat there is given 2 kilograms of lime per piece of cloth. To the vitriol vat there is added 50 kilograms of sulphate of iron for each dozen pieces. The soda vat is renewed after 5 pieces by the addition of 12 kilograms of salt of soda, which has first been made caustic. The acid vat receives 25 kilograms of acid after 5 pieces, and ought to be renewed whenever it becomes saline. The other vats must be cleared out whenever the deposit becomes too great for success. M. Ed. Schwartz recommends as important conditions, (1) the perfect causticity of the tissue, and an average strength of 140 Beaumé; (2) the neutrality of the sulphate of lime vat. For this end old iron should be boiled in it. After leaving the sulphuric acid vat the pieces are rinsed in the water vat, then in river water, and afterwards should be soaked in a sulphuric acid bath at 40 Beaumé, for the purpose of dissolving the last traces of the peroxide of iron adhering to the fibre. The fabric is then washed in water and finally passed through a soapy water at 40° R. _Solid or precipitated blue, Schutzenberger’s receipt_.—The process consists in printing indigo white precipitated in a vat, in a thick paste to dissolve it on the tissue by a passage through an alkaline bath (lime or soda), and of reprecipitating it by oxidizing it as soon as it has entered the fibre. It is then the china blue process, minus the reduction which is made before printing, and consequently minus the sulphate of iron vat. Indigo white is too alterable to be printed with success, so it is generally precipitated in combination with a stannic hydrate (hydrate of a salt of tin), which gives it body and preserves it from a too rapid oxidation. The stannic indigotate in paste, or as it is generally called precipitate of indigo, is prepared by turning into the clear portion of a strong copperas vat an acid solution of protochlorate of tin, and filtering it upon woollen filters,—as much as possible away from the air. It would be better to prepare a strong tin vat by heating a mixture of indigo, caustic soda, and protochlorate of tin, and to precipitate by chlorohydric acid.[9] ------------------------------------------------------------- [9] Mr. T. P. Shepard gives in his valuable “Receipts for Calico Printing,” published in 1872, the following:— NO. 52. INDIGO PRECIPITATE FOR FAST BLUE AND GREEN. 10 pounds quicklime, slacked with 6½ gallons water; then 2 pounds ground indigo finely rubbed in water are stirred in; then add 6 pounds copperas dissolved in 5 gallons of water; then add 5 gallons hot water and 15 gallons cold water. Stir well from time to time, until the liquid has assumed a yellow color and deep blue veins or streaks appear on its surface. When this moment arrives, draw off the clear liquor, and precipitate every ten quarts of it with ½ pound tin crystals, dissolved in ½ pound muriatic acid.