Bichromates.—The bichromates are usually of a red or reddish-brown colour, those of the alkali metals being readily soluble in water. They are readily decomposed by heat, leaving a residue of the normal chromate and chromium sesquioxide, and liberating oxygen; ammonium bichromate, however, is completely decomposed into chromium sesquioxide, water and nitrogen. Sulphuretted hydrogen and sulphur dioxide reduce them in acid solution to the condition of chromium salts.
Potassium bichromate, K2Cr2O7, is obtained by fusing chrome ironstone with soda ash and lime (see above), the calcium chromate formed in the process being decomposed by a hot solution of potassium sulphate. After the calcium sulphate has settled, the potassium chromate solution is converted into bichromate by the action of sulphuric acid, and the salt is allowed to crystallize. It forms large triclinic prisms of specific gravity 2.6-2.7, which are moderately soluble in cold water and readily soluble in hot water. The solution is strongly acid in reaction and is very poisonous. Potassium bichromate finds extensive application in organic chemistry as an oxidizing agent, being used for this purpose in dilute sulphuric acid solution, K2Cr2O7 + 4H2SO4 = KaSO4 + Cr2(SO4)3 + 4H2O + 3O. On the addition of concentrated sulphuric acid to a cold saturated solution of the salt, red crystals of chromium trioxide, CrO3, separate (see [Chromium]), whilst when warmed with concentrated hydrochloric acid and a little water, potassium chlorochromate is produced. When heated with phosphorus trichloride in a sealed tube to 160° C., potassium chlorochromate, phosphorus oxychloride, potassium chloride, and a complex chromium oxide (possibly Cr3O6) are produced (A. Michaelis, Jour. prak. Chem., 1871, ii. 4, p. 452). Potassium bichromate finds application in photography, in calico-printing and in the preparation of bichromate cells. Sodium bichromate, Na2Cr2O7·2H2O, may be obtained by the addition of the requisite quantity of chromium trioxide to a solution of sodium chromate. It crystallizes in hyacinth-red prisms, which are very hygroscopic and melt at 320° C.
Trichromates.—The trichromates are obtained by the addition of nitric acid (of specific gravity about 1.2) to solutions of the bichromates. They form rhombic crystals of a red or brown red or brown red colour and are readily decomposed by warm water, with formation of the bichromate.
Perchromic Acid.—By the addition of hydrogen peroxide to a solution of chromic acid, a fine blue coloration due to a perchromic acid is produced which is readily absorbed by shaking out with ether. The following formulae have been assigned to the compound:—H2O2·CrO3 (H. Moissan, Comptes rendus, 1883, 97, p. 96); H2O2·2HCrO4 (M. Berthelot, Comptes rendus, 1889, 108, p. 25); Cr2O7·xH2O (L.C.A. Barreswil, Ann. chim. et phys., 1847 [3], 20, p. 364), and CrO6·3H2O (T. Fairley, Chem. News, 1876, 33, p. 237). The more recent investigations of H.G. Byers and E.E. Reed (Amer. Chem. Jour., 1904, 32, p. 503) show that if metallic potassium be added to an ethereal solution of the blue compound at −20° C., hydrogen is liberated and a purple black precipitate of the perchromate, of composition KCrO4 or K2Cl2O8, is produced; this compound is very unstable, and readily decomposes into oxygen and potassium bichromate. Similar sodium, ammonium, lithium, magnesium, calcium, barium and zinc salts have been obtained. It is shown that the blue solution most probably contains the acid of composition, H2Cr2O8, whilst in the presence of an excess of hydrogen peroxide more highly oxidized products probably exist.
BICKER (connected by Skeat with bike, to thrust or strike), an Old English word (traced from the 13th century) implying conflict or disputation. A poetical use, from the noise, is seen in Tennyson’s Brook, “to bicker down the valley.”
BICKERSTAFFE, ISAAC (c. 1735-c. 1812), English dramatist, was born in Ireland about 1735. At the age of eleven he was appointed a page to Lord Chesterfield, then lord lieutenant of Ireland, and subsequently held a commission in the Marines, but was dismissed the service under discreditable circumstances. He was the author of a large number of plays and burlesque farces interspersed with songs, produced between 1760 and 1771. The best-known are Maid of the Mill (founded on Richardson’s Pamela), The Padlock, He Would if he Could, Love in a Village, The Hypocrite and The Captive. In 1772 Bickerstaffe, suspected of a capital offence, fled to the continent. The exact date of his death is unknown, but he is stated to have been still living in abject misery in 1812.
A full account of his dramatic productions is given in Biographia Dramatica, edited by Stephen Jones (1812).