IT is not yet known who first discovered the curious suspension of chemical action often noticed between carefully dried substances which, in ordinary circumstances, react with one another. So far back as 1802, Mrs. Fulhame * pointed out that gold salts are not reduced either * by hydrogen or by (' phosphorated ether " unless first moistened with water, and she suggested a theory to account for the influence of water in chemical reactions. Higgins," in 1814, observed that " dry muriatic acid

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... no action on dry calcareous earth, while these substances readily unite if moisture is present." I n 1837, BonsdorfE (Ann. Phys, Chern., 1837, 41, 293; 42, 325) demonstrated that atmospheric air freed from carbon dioxide and moisture does not tarnish clean surfaces of metallic potassium, arsenic, + f bismuth, lead (commercial or pure), zinc, cadmium, iron, or copper ; in 1838, Regnsult (Ann. Chim. Phys., 1838, [ii], 60, 176) failed to induce dry olefiant gas to combine with chlorine in diffused daylight ; E. A. Parnell (B.A. Reports, 1841, 51) drew attention t o the important part pIayed by water in chemical reactions and showed that whilst moist hydrogen sulphide acts vigorously on papers impregnated with salts of lead, mercury, and copper, there is no action if the hydrogen sulphide is well dried; and Andrews, in 1842, stated in a foot-note to one of his papers (Trans. Roy. Irish. Acad., 1842, 19, 398; or S c i e n t 9 c Memoirs, 1889, p. 90) that although moist chlorine combines energetically with zinc, copper, and iron-filings, perfectly dry chlorine " has no action whatever at ordinary temperatures . . . . the same remarks may be applied to the behaviour of dry bromine in contact with dry metals." Kolb (Compt. rend., 1867, 64, 861; see also Debray, ibid., 1848, 26, 603) showed, in 1867, that dried oxides and hydroxides of calcium, barium, magnesium, sodium, and potassium do not increase in weight in a n atmosphere of dry carbon dioxide. I n 1869, came Wanklyn's observations (Chern. News, 1869, 20, 271) that sodium and chlorine do not unite; this is sometimes said to be the earliest record of the influence of small quantities of water in promoting chemical action, although, as Dixon (Trans., 1896, 69, 775) has pointed out, Wanklyn does not state whether moisture has any effect or not on the combination. Dubrunfaut (Compt. rend., 1871, 73, 1395 was under the impression that water assists the combustion of carbon, but his experiments were far from being conclusive, and he did not reply to Dumas' statement (Compt. rend., 1872, 74, 13) that pure graphite burns completely in oxygen dried by sulphuric acid. I n 1880, Dison (B.A. Reports, 1880, 593) opened up the way for systematic research on this subject. Baker (Trans., 1894, 65, 611) has compiled a list of papers published between that date and 1894. W e have made some experiments with the object of finding whether pure chlorine will combine with dry hydrogen. Armstrong, in his * Higgins' Experimem% and Observations on the Atomic Theory, 1814 ; we are indebted to the kindness and courtesy of Dlr. V. H. Veley for these two references. t Bonsdorff states that Bergmann had previously demonstrated that dry air had no action on metallic arsenic.