Neutral Chromate of Potash, CrO3K2O = 194·7, containing 56·7 per cent. of its weight of chromic anhydride, CrO3.—This salt is in the form of citron-yellow rhombic crystals, easily soluble in water, but insoluble in alcohol. Its aqueous solution is precipitated yellow by lead acetate or basic acetate; the precipitate being insoluble in acetic acid. If chromate of potash in solution is tested with silver nitrate, the red chromate of silver is thrown down; the precipitate is with difficulty soluble in dilute nitric acid.
§ 884. Potassic Bichromate, CrO3K2O = 295·2, containing 68·07 per cent. of its weight of chromic anhydride, CrO3.—This salt is in beautiful large, red, transparent, four-sided tables; it is anhydrous and fuses below redness. At a high temperature it is decomposed into green oxide of chromium and yellow chromate of potash. It is insoluble in alcohol, but readily soluble in water. The solution gives the same precipitates with silver, lead, and barium as the neutral chromate. On digesting a solution of the bichromate with sulphuric acid and alcohol, the solution becomes green from the formation of chromic oxide.
§ 885. Neutral Lead Chromate, PbCrO4 = 323·5, composition in 100 parts, PbO, 68·94, CrO3, 31·06.—This is technically known as “Chrome Yellow,” and is obtained as a yellow precipitate whenever a solution of plumbic acetate is added, either to the solutions of potassic chromate or bichromate; by adding chrome yellow to fused potassic nitrate, “chrome red” is formed; it has the composition CrO32PbO. Neutral lead chromate is insoluble in acids, but may be dissolved by potassic or sodic hydrates.
§ 886. Use in the Arts.—Potassic bichromate is extensively used in the arts—in dyeing, calico-printing, the manufacture of porcelain, and in photography; the neutral chromate has been employed to a small extent as a medicine, and is a common laboratory reagent; lead chromate is a valuable pigment.
§ 887. Effects of some of the Chromium Compounds on Animal Life.—In the chromates of potash there is a combination of two poisonous metals, so that it is not surprising that Gmelin found the chloride of chromium, CrCl3, less active than the neutral chromate of potash; 1·9 grm. of the last, administered to a rabbit by the stomach, caused death within two hours, while 3 grms. of chromous chloride had no action. Subcutaneous doses of ·2 to ·4 grm. of neutral chromate (according to the experiments of E. Gergens[960] and Carl Posner[961]) act with great intensity on rabbits. Immediately after the injection the animals are restless, and show marked dyspnœa; death often takes place within a few hours.
[960] Arch. f. experiment. Pathol. u. Pharmakol., Bd. 6, Hft. 1 and 2, § 148, 1875.
[961] Virchow’s Archiv f. path. Anat., Bd. 79, Hft. 2, § 333, 1880.
Diarrhœa does not seem, as a rule, to follow when the salt is administered by subcutaneous injection to animals; but Gmelin’s rabbits had considerable diarrhœa when 1·9 grm. was introduced into the stomach. The same quantity, injected beneath the skin of a dog, caused loss of appetite, and, after six days, there was a dry exanthem on the back, and the hair fell off in patches; there was, however, neither diarrhœa nor vomiting. Bichromate of potash causes (according to the researches of Pelikan)[962] symptoms similar to those produced by arsenic or corrosive sublimate; it acts as a powerful irritant of the stomach and intestinal canal, and may even cause inflammation; on its absorption a series of symptoms are produced, of which the most prominent are albuminuria, bloody urine, and emaciation. From ·06 to ·36 grm. (1-51⁄2 grains) is fatal to rabbits and dogs.