[30] “In the annual report on the progress of chemistry, presented to the Royal Academy of Stockholm, in March 1840, I have proposed to designate by the term _allotropic state_, that dissimilar condition which is observed in certain elements, and long known examples of which are found in the different forms of carbon, as graphite and diamond. “Although these dissimilar conditions, which I have here called allotropic, have long since attracted attention in one or two elements, still they have been regarded as exceptions to the general rule. It is at present my object to show that they are not so rare; that it is probably rather a general property of the elements to appear in different allotropic conditions; and that although we have hitherto been unable to obtain several of the elements when uncombined in their allotropic states, still their compounds indicate the same with tolerable distinctness.”--_Berzelius on the Allotropy of the Elementary Bodies_, _&c._: Poggendorff’s Annalen, 1844. Scientific Memoirs, vol. iv. p. 240. [31] “Copper, when reduced by hydrogen at a heat below that of redness, on exposure to air soon becomes converted throughout its mass into protoxide; and when it is triturated for some time with an equivalent quantity of sulphur, it combines with it according to Böttcher’s experiments, producing flame, and forming sulphuret of copper. If, however, the copper be reduced by hydrogen at a red heat, still considerably below the temperature at which it softens and begins to melt, it remains for years unchanged by exposure to air, and cannot be made to combine with sulphur without the application of heat. Iron, cobalt, and nickel, when reduced by hydrogen below a red heat, inflame after they have cooled, if exposed to the air; and if they are immediately placed in water to avoid their taking fire, they inflame when they are again removed, and have become nearly dry. If we compare this behaviour with that of iron reduced by heat, and with iron in that state in which it forms the conductor of a galvanic current without becoming oxidized, it would appear that these peculiarities depended upon something more than a difference of mechanical condition.”--_Berzelius on the Allotropy of Elementary Bodies._ See _On the Isomeric Conditions of the Peroxide of Tin_: by Prof. H. Rose.--Chemical Gazette, Oct. 1848. [32] On this curious subject, and its history, see Bergman’s _Dissert. de Phlog. quantitate in Metallis_, 1764. Kirwan, _On the Attractive Powers of Mineral Acids_: Philosophical Transactions. Kier’s _Experiments and Observations on the Dissolution of Metals in Acids_: Phil. Trans. 1790.