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DYEING AND CALICO PRINTING.

is, when used, fixed by means of albumen, but may be fixed chemically byprinting on a mixture of acetate of copper and arsenious acid, and steaming;or by rinsing the fabric previously treated with arsenite of copper through abath of acetic acid.

The colours derived from insoluble salts of chromium are numerous, andalthough with the present valuable innovation of aniline dyes it is improbablethat chrome or mineral pigments will meet with greatly extended application,we may shortly review the characteristics of the principal green pigments.

Arnaudon green, or metaphosphate of chromium, is a very similar colour toSchweinfurt green, but less vivid. According to M. Arnaudon it is best pre-pared by mixing equivalent parts of neutral phosphate of ammonia and ofbichromate of potassium (128 parts of phosphate and 149 parts of bichromate).The salts are pulverised together or dissolved simultaneously in a very littlewater, and the liquid is evaporated until it can be removed in the mass oncooling. The product is placed in a vessel, and heated upon an oil-bath to180°. Should the temperature rise beyond 200° the green colour will havedisappeared. The result of this process is washed in water, leaving a finepowder of a colour approaching that of budding leaves. The loss of colourat too high a temperature is probably due to the reduaion of the bichromatein excess by the ammonia of the phosphate.

Plessy green is obtained, according to the inventor, by dissolving 1 part ofbichromate of potassium in 10 parts of boiling water, and throwing in 3 litresof biphosphate of lime and 1-25 kilos, of powdered sugar. A large quantity ofgas is quickly disengaged, and when the aaion is no longer apparent theliquid is decanted, and the precipitate washed in water.

This green does not suffer alteration by exposure to the action of the air,or of sulphuretted hydrogen. For printing this colour is too pale, but it hasmet with several applications.

BLUE AND VIOLET PIGMENTS.

Blue and violet pigments include ultramarine, the blue colours derived fromcyanogen and ferro-cyanogen compounds, cobalt blue, Thenard blue, smalt,phosphate of cobalt, ceruleum, the blue oxides of some of the rarer metals,as for instance, molybdenum blue, tungsten blue, and a few others.

Ultramarine.

The artificial production of this magnificent pigment is one of the greatestconquests of modern chemistry, and is due entirely to the labours of Messrs.Guimet and Gmelin, working, however, independently of each other. Themineral known by several names, but generally called lapis lazuli, or simplylapis, is one of the rather rare substances found disseminated through apeculiar kind of granite, especially in Central Asia. Although it was knownin Europe as far back as the times of Raphael and Michel-Angelo (both theseartists employed it), its true composition remained a secret until the begin-ning of this century; but it is from the results of the quantitative analysisof this mineral that the manufacture of artificial ultramarine has taken itsorigin. The characteristic difference between native and artificial ultramarineis that the native pigment, as obtained by lixiviation of the pulverised mineral,is not acted upon by strong or distilled vinegar, nor by a concentrated solution