Chromate of Potash, adulteration of, to detect

The chromate of potash has the power of combining with other salts up to a certain extent without any very sensible change in its form and appearance; and hence it has been sent into the market falsified by very considerable quantities of sulphate and muriate of potash, the presence of which has often escaped observation, to the great lo of the dyers who use it so extensively. The following test proce has been devised by M. Zuber, of Mulhouse. Add a large exce of tartaric acid to the chromate in question, which will decompose it, and produce in a few minutes a deep amethyst colour. The supernatant liquor will, if the chromate be pure, afford now no precipitate with the nitrates of barytes or silver; whence the absence of the sulphates and muriates may be inferred. We must, however, use dilute solutions of the chromate and acid, lest bitartrate of potash be precipitated, which will take place if le than 60 parts of water be employed. Nor must we test the liquid till the decomposition be complete, and till the colour verge rather towards the green than the yellow. Eight parts of tartaric acid should be added to one of chromate to obtain a sure and rapid result. If nitrate of potash (saltpetre) is the adulterating ingredient, it may be detected by throwing it on burning coals, when deflagration will ensue. The green colour is a certain mark of the transformation of the chromic acid partially into the chrome oxide; which is effected equally by the sulphurous acid and sulphuretted hydrogen. Here this metallic acid is dis oxygenated by the tartaric, as has been long known. The tests which I should prefer, are the nitrates of silver and baryta, having previously added so much nitric acid to the solution of the suspected chromate, as to prevent the precipitation of the chromate of silver or baryta. The smallest adulteration by sulphates or muriates will thus be detected. CINNABAR; the native red sulphuret of mercury. It occurs sometimes crystallized in rhomboids; has a specific gravity varying from 6·7 to 8·2; a flat conchoidal fracture; is fine grained; opaque; has an adamantine lustre, and a colour pa ing from cochineal to ruby red. The fibrous and earthy cinnabar has a scarlet hue. It is met with di eminated in smaller or larger lumps in veins, which are surrounded by a black clay, and is a ociated with native quicksilver, amalgam with iron-ore, lead-glance, blende, copper-ore, gold, . Its principal localities are Almaden in Spain, Idria in the Schiefergebirge, Kremnitz and Schemnitz in Hungary; in Saxony, Bavaria, Bohemia, Na au, China, Japan, Mexico, Columbia, Peru. It consists of two primes of sulphur, = 32·240, combined with one of mercury, = 202,863; or in 100 parts of 12·7 sulphur + 87·3 mercury. It is the most prolific ore of this metal; and is easily smelted by exposing a mixture of it with iron or lime to a red heat in retorts. Factitious cinnabar is called in commerce Vermillion , which see, as also Mercury .