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 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 ), 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).

 BICKERSTETH, EDWARD (1786–1850), English evangelical divine, brother of Henry, Baron Langdale, master of the rolls (1836–1851), and uncle of Robert Bickersteth, bishop of Ripon (1857–1884), was born at Kirkby Lonsdale, and practised as a solicitor at Norwich from 1812 to 1815. In 1816 he took orders, and was made one of the secretaries of the Church Missionary Society. On receiving the living of Watton, Hertfordshire, in 1830, he resigned his secretaryship, but continued to lecture and preach, both for the Church Missionary Society and the Society for the Conversion of the Jews. His works include A Scripture Help (London, 1816), which has been translated into many European languages, and Christian Psalmody (London, 1833), a collection of over 700 hymns, which forms the basis of the Hymnal Companion (London, 1870), compiled by his son, E. H. Bickersteth, bishop of Exeter (1885–1890). He was active in promoting the Evangelical Alliance of 1845, strongly opposed the Tractarian Movement, and was one of the founders of the Irish Church Missions, and Parker, Societies.

(1814–1892), dean of Lichfield, was his nephew, and (1850–1897), bishop of South Tokyo, his grandson.

 BICYCLE (from prefix bi = twice, and a circle, wheel). The modern bicycle, as developed from the old velocipede (see ), consists essentially of two wheels placed one behind the other and mounted on a frame which carries a saddle for the rider. Between the wheels is a crank-axle which the rider drives by means of the cranks and pedals, and its motion is transmitted to the rear or driving wheel either by a chain which passes over two chain wheels, one fixed on the crank-axle and the other on the hub of the rear wheel, or, in the chainless bicycle, by a tubular shaft and two pairs of bevel-wheels. The rear wheel is usually so arranged that it can turn, when the bicycle is running by its own momentum, independently of the chain and pedals (“free-wheel”), and a variable speed gear is often provided so that the rider may at will alter the ratio between the rate of revolution of the crank-axle and the driving wheel. The front, or steering wheel, is mounted in a fork having its two upper ends brazed into the “crown,” to which also the lower end of the steering tube is brazed. The steering tube is mounted by ball bearings in the socket tube, which forms the forward portion of the rear-frame.

The highest quality of materials and the most accurate workmanship are required to produce a first-class bicycle. Steel of 75 to 100 tons per sq. in. tensile strength is used in chains, spokes, &c. In balls and ball-races, hardness without brittleness, and homogeneity are of primary importance. Broken balls, or even traces of wear in bearings, are now seldom heard of in a first-class bicycle. The process of case-hardening, whereby an extremely hard outer skin is combined with a tough interior, has been brought to a high degree of perfection, and is applied to many parts of the bicycle, particularly chains, free-wheels and toothed-wheel variable speed gears. Interchangeability of parts is secured by working to the smallest possible limits of error of workmanship.

Frames.—Fig. 1 represents a road-racer. A full roadster would have the handles a little higher relatively to the saddle, and would be provided with mud-guards, free-wheel and sometimes a gear-case and variable speed gear. Fig. 2 shows a lady’s bicycle with gear-case and dress-guard. The rear frame of the “diamond” type (fig. 1) is subjected to very small stresses due to vertical load. The front fork and steering post are subject to bending moment due to the reaction from the ground in the direction dcb. A slight amount of elasticity in the front fork adds considerably to the comfort in riding over rough roads. When the brake is applied lightly to the front wheel, the reaction from the ground falls more closely along the axis of the front fork, and the bending moment at the crown is diminished. If the front brake is applied harder the reaction from the ground at d may pass through the crown, in which case the bending moment at the crown is zero. Still harder application of the brake causes a bending moment in the opposite direction. In fig. 1 the axes of the top and bottom tubes of the rear frame are produced to meet at a.