_China blue_.—The theory of this printing blue, says Schutzenberger, is very simple. The indigo, reduced to an impalpable powder and thickened, is printed by a plate or roller. After drying, the tissue seems dyed blue, more or less deep, according to the proportion of coloring material used; but it is only a blue of application, which can be removed with the thickening, by the slightest washing. The object is now to reduce and redissolve the indigotine in place to enable it to penetrate the fibre at the end of a consecutive oxidization, and without producing a running of the color or altering the purity and distinctness of the contours of the design. I owe to M. Ed. Schwartz some valuable hints upon the fabrication of this style, which is also described with much care and details in the treatise on printing by M. Persoz. The reduction of the indigo is obtained by alternate passages of the printed tissue into vats containing,—the first, quicklime slacked; the second, sulphate of iron; the third, soda. The operation is terminated by a passage through a bath of sulphuric acid, which removes the oxide of iron and precipitates the indigo white by hastening its oxidation. The success depends upon the composition of the color printed, and above all upon the strength of the vats of immersion and the duration of the treatment. The operator uses six vats,—for instance, two lime vats, provided each with 12 kilograms of lime; a copperas vat at 70 Beaumé; a caustic soda vat marking 140 Beaumé; a sulphuric acid vat with 500 grammes of acid (_par mesure d’eau_); and finally a vat of pure water. The receipts for printing are:— 1. THE BLUE PREPARATION. Ground indigo 4 kilograms. Acetate of iron 10 litres. Sulphate of iron 1 kilogram. Water 10 litres. Gum Senegal 6 kilograms. Pass through a sieve; leave some time at rest, and stir whenever used. Caraccas indigo is preferred because it can be broken into a finer powder and gives a finer paste. 2. COLORS FOR ROLLER PRINTING NOS. 1, 2, 3, 4. The blue preparation above 1, 1, 3, 4. Acetate of iron containing 700 grammes of gum per litre 2, 1½, ½, ½. Gum water at 600 grammes per litre 16, 2½, ½, ½. These proportions can be varied according to the tint desired. The piece is treated a quarter of an hour in the first lime vat by giving it a light movement from above to below; it is left a quarter of an hour in repose in the sulphate of lime vat; a quarter of an hour in the second lime vat; a quarter of an hour in the copperas vat; five minutes in the caustic soda; half an hour in the sulphuric acid, and then thoroughly rinsed.