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DYEING AND CALICO PRINTING.

ultramarine is the immediate produdt of the calcination. The process, how-ever, is difficult to manage, on account of the tendency to fusion amongst thematerials employed.

CYANOGEN COLOURS.

The colouring materials of this group are—

Prussian blue;

Soluble Prussian blue;

Turnbull’s blue (two varieties);

Tin blue (two varieties); and

Havraneck’s green, or prussiate of chromium.

All these preparations are obtained by means of the yellow and redprussiates, or, as they are scientifically called, ferro- and ferri-cyanide ofpotassium. Prussian blue or Berlin blue was quite accidentally discoveredin the year 1710, by Diesbach, at Berlin, whence its name. It was onlytowards the end of last century that Scheele discovered the relation existingbetween Berlin blue (ferrocyanide of cyanide of iron) and the yellow prussiate.This salt is technically a very important substance. It contains in 100 parts—Potassium, 37-03 ; cyanogen (carbon, 17-04 ; nitrogen, iq-8g); iron, 13-25; water,I2'7g. It is considered either as a combination of ferro-cyanogen with potassiumand water (Fe3Cy = Cfy)2fC+3HO ; or as a combination of protocyanide of iron(FeC 2 N = FeCy) with cyanide of potassium and water, FeCy+ 2KCy + 3HO.The salt crystallises in large, deep, lemon-coloured crystals. It loses its waterof crystallisation at 100°; dissolves in four times its weight of cold, andin a little more than its own weight of boiling water; insoluble in strongalcohol, which precipitates its aqueous solution. The specific gravity of itsconcentrated solution at 8° C. is 1-130; the specific gravity of the salt is1-833. Heated to a dull red heat, with exclusion of air, and having beendeprived of its water, the salt fuses, is decomposed, gives off nitrogen, andleaves a residue of cyanide of potassium and carbide of iron ; but ifany water has been left, and oxygen has access during this ignition, carbonicacid and ammonia are simultaneously given off. A mixture of 8 parts of driedferrocyanide and 3 parts of carbonate of potash yields, on fusion, cyanide ofpotassium, carbonic acid and carbonic oxide, and peroxide of iron. The yellowprussiate and its aqueous solution are slowly decomposed by the adtion of day-light, hydrocyanic acid is given off, and there is formed either Prussian blueor oxide of iron; the solution assumes an alkaline readtion. The yellowprussiate is manufadtured on the large scale : the rationale of the process isthat as soon as nitrogenous substances, preferably of animal origin,—horn,blood, refuse wool, leather, and similar materials,—are ignited with potash(carbonate or any other salt of potash decomposable by heat and carbon), andsome iron-filings or borings, there are produced, by a complicate readtion,potassium and sulphide of potassium ; the sulphur of the latter is transferredto the iron, and, by the intervention of the potassium and carbon, cyanogen isformed, which in its turn combines with the potassium. It should be borne inmind that cyanide of potassium resists, i. e. is not decomposed by, very intenseheat. After cooling there does not exist in the fused mass ferrocyanide readyformed, but only cyanide of potassium and iron, and of course carbonaceousmatter; the ferrocyanide of potassium is obtained by lixiviating the fusedmass with water. The so-called red prussiate consists, in 100 parts, of