Page:Dictionary of National Biography, Third Supplement.djvu/504

 .general. At the same time he was advanced to the dignity of K.C.I.E., in recognition of the part which he had played in the recent Bazar valley campaign, which brought him also the Swedish military order of the Sword.

Roos-Keppel's service of eleven years in his new post included the period of the European War, during which his presence on the Indian frontier was of inestimable value. Skilled in all the local dialects and intimately acquainted with the customs and traditions of the border tribes, he was able to win their affection by his sympathy, while gaining their respect by the mingled patience and firmness with which he ruled them. He always had in view the permanent pacification of the province, and its material well-being; and for this reason he paid great attention to the spread of education. His popularity with the tribes enabled him to keep the frontier quiet until the spring of 1919, when war with Afghanistan became inevitable; his presence at Peshawar was then a tower of strength, and great was the regret when, in the autumn of that year, increasing ill-health forced him to relinquish his post and return to England. The government, however, was unwilling to lose the benefit of his assistance, and he was immediately appointed to the council of the secretary of state for India, where his experience and judgement gave him great weight in all political questions. His health broke down completely in August 1921, and after a trying illness he died in London on 11 December of that year. Roos-Keppel had been made a G.C.I.E. in 1917, and at the time of his death he was also a knight of grace of the order of St. John of Jerusalem. He had never married.

 ROSCOE, HENRY ENFIELD (1833–1915), chemist, was born in London 7 January 1833. His father, Henry Roscoe [q.v.], judge of the court of Passage, Liverpool, was the youngest son of William Roscoe [q.v.], banker, well known for his biographies of Lorenzo de' Medici and Pope Leo X; his mother, Maria, daughter of Thomas Fletcher, a Liverpool merchant, was granddaughter of William Enfield [q.v.], the last rector of the Warrington Academy. Roscoe began his scientific training at the high school of the Liverpool Institute under W. H. Balmain, known for his ‘luminous paint’. In 1848 he entered University College, London, and worked in the Birkbeck laboratory under Alexander William Williamson [q.v.] who, on succeeding Thomas Graham [q.v.] as professor of chemistry, appointed Roscoe his assistant. Gaining his B.A. degree with honours in chemistry in 1852, Roscoe proceeded to Heidelberg to work under R. W. von Bunsen, and on graduating Ph.D. in 1854 began his long research with Bunsen on the measurement of the chemical action of light. The reaction chosen was the gradual union of hydrogen and chlorine under the influence of light, originally observed by John Dalton [q.v.]. This had been investigated in 1843 by John William Draper [q.v.], who had demonstrated the initial ‘inert period’ and its abolition by the sun shining on the chlorine standing over water previous to its mixture with hydrogen. Bunsen and Roscoe made many experiments without being aware of Draper's work; on learning of it they repeated his experiment on the abolition of the inert period and found that ‘insolated’ chlorine, when mixed with hydrogen over water, still exhibited ‘photo-chemical induction’. This delay was afterwards proved to be due to a minute trace of an ammonia compound which had been destroyed in Draper's experiment. By the preparation of a standard photographic paper Roscoe secured a ready means of comparing the light of the sun at different altitudes, and of measuring the diffused light from the sky.

Soon after Roscoe's return to England he was elected (1857) to the chair of chemistry vacated by (Sir) Edward Frankland at the Owens College, Manchester. He came to Manchester when the college (opened in 1851) had reached its lowest ebb, but he grasped the great need for scientific education in an industrial centre, and the success of the chemistry school under Roscoe was a large factor in the rise of the college in efficiency and public estimation.

Roscoe's most important contribution to chemistry was the preparation of pure vanadium, and the proof which he gave from the study of its oxides and chlorides that vanadium was a member of the phosphorus-arsenic family, and not related to chromium as J. J. Berzelius had supposed. The new atomic weight assigned by Roscoe to vanadium fitted it for its rightful place in the fifth group when D. I. Mendeléeff published his Periodic System (1869). Roscoe's Lessons in Elementary Chemistry (1866) passed through 478