Page:1902 Encyclopædia Britannica - Volume 26 - AUS-CHI.pdf/764

 708

CHEMISTRY. blast-furnace metal; although, according to their estimate, only 1 part is present in 30,000 of the iron, the proportion is larger than in any other known material. Scandium = Ekaboron.—The existence of this element was first noticed by Nilson in 1879, in the course of an examination of ytterbia prepared by Marignac’s method from the rare mineral gadolinite. Cleve, who had succeeded in carrying the purification much further, shortly afterwards gave a description of the properties of scandium—remarkable for its completeness in view of the very small amount of material at his disposal—in which he proved that it corresponds to Mendeleeff’s hypothetical ekaboron. According to Cleve, it is present in gadolinite and yttrotantalite to the extent of only about 0-005 per cent., but euxenite, according to Nilson, contains a larger proportion. Germanium = Ekasilicium.—The original source of this element, and the only one known up to the present time, is argyrodite, a double sulphide of silver and germanium, Discovery of New Elements. 3Ag.2S.GeS2 (Jour, prakt. Chem. 1886, 34, p. 177), of which To deal first with the question of new elements. An several hundred kilogrammes were found in 1885 quite interval of no less than twelve years elapsed between the locally deposited in an adit in the Himmelsfurst mine discovery of indium (in 1863) and that of another new near Freiberg. Clemens Winkler was led to recognize element, gallium (in 1875), but since the latter date our the presence of a new element in this mineral in conseknowledge of the elements—the primary materials with quence of the difficulties he experienced in effecting its which the chemist works—has been very considerably analysis. Since thoria has been required in quantity for the extended, ten or more having been added to the list, and now the number of well-defined species borders on eighty. manufacture of the mantles devised by Auer von WelsSuch discoveries serve a far higher purpose than that of bach as a means of producing the incandescent gas Yttrium,n gratifying the mere collector’s instinct, for the introduction light, new and abundant sources of the minerals cer/"^ ' of law among the elements has led us to realize that in which it is contained have been discovered, group. progress in our knowledge of the true relationships The attendant earths are consequently almost subsisting between them generally depends more on the waste products, and the designation “rare earths,” completion of the record than on anything else. As which has so long served to characterize the oxides of Mendeleeff himself pointed out in his Faraday lecture the yttrium-cerium group of elements, is scarcely applicable. The field of work that these elements present is {Trans. Chem. Soc. 1889, p. 634) :— Before the promulgation of the periodic law the chemical ele- one of extraordinary difficulty, and we are clearly still ments were mere fragmentary incidental facts in nature ; there was but at the threshold of knowledge. The history of disno special reason to expect the discovery of new elements, and the covery in this branch of chemistry has been set out in new ones which were discovered from time to time appeared to be a clear and concise manner by the Scandinavian chemist possessed of quite novel properties. The law of periodicity first Cleve—the highest living authority on the group—in enabled us to perceive undiscovered elements at a distance which formerly were inaccessible to chemical vision, and long ere they a lecture delivered in memory of the Swiss chemist were discovered new elements appeared before our eyes possessed Marignac, who specially devoted himself to the investiof a number of well-defined properties. gation of the rare earths (Trans. Chem. Soc. 1895, p. 468). Mendeleeff here refers to the fact that in his original S Crookes, a noted worker in this field, who has added very essay he fully described in advance the properties of three j largely to the methods of discriminating the rare earths, elements, which he named ekaaluminium, eka- ; has fully discussed the question of the individuality of Predicted anc[ ekasilicium, and that elements were the various earths in two presidential addresses to the elements. supsequenp[y discovered which were found to be Chemical Society of London (Trans. Chem. Soc. 1888, p. endowed with properties for the most part in closest accord 487 ; 1889, p. 257). Cleve classes the elements of the with his predictions. Indeed it is from this circumstance group in two divisions—one containing “ perfectly charmore than any other, perhaps, that the periodic law at an acterized,” the other “not yet thoroughly characterized ” early date acquired its extreme popularity. It will be elements. The former includes the following four new evident from the following brief statements that the circum- elements:— Ytterbium.—This element was isolated by Marignac in stances attending the discovery of new elements in recent 1878 from erbia separated from gadolinite, and was subtimes have often been of peculiar interest:— Gallium = Ekaaluminium.—The discovery of gallium sequently studied by Nilson. It yields a white oxide and was made in 1875 by Lecoq de Boisbaudran (C. R. 81, colourless salts ; its spark spectrum is rich in lines, although p. 493, cf. Ann. Phys. Chim. (6) 2, p. 176), who was led by its salts have no absorptive effect. Samarium.—Attention was called to the existence of a means of the spectroscope to recognize its presence in new element in the earths from samarskite in 1878, first very minute proportion in a zinc blende from the Pyrenees. He afterwards found it in blendes from other sources. by Delafontaine, and soon afterwards by Lecoq de BoisAlthough a very rare element, gallium seems to be widely baudran ; their observations were extended by Marignac distributed : thus Hartley and Ramage have shown that in 1880, but we owe our knowledge of samarium mainly it is present in Cleveland iron ores (Proc. R. Soc. 1896, to Cleve (Trans. Chem. Soc. 1883, p. 362 ; cf. Betten60, p. 393), and have even separated it from the crude dorf, Liebig’s Annalen, 1891, 263, p. 164). The oxide of

THE final paragraph of the article Chemistry in the Encyclopaedia Britannica, ninth edition, vol. v. p. 544, although written at a time when Mendeleeff’s classical essay, clearly defining the periodic character of the relationship among the elements, was barely five years old, may well be taken as an appropriate introduction to the present supplementary article, as calling attention to important points of view from which it is desirable, in the first instance, to consider the progress that has been made. It is as follows :— The establishment of the periodic law may truly be said to mark an era in chemical science, and we may anticipate that its application and extension will be fraught with the most important consequences. It reminds us how important above all things is the correct determination of the fundamental constants of our science —the atomic weights of the elements, about which in many cases great uncertainty prevails ; it is much to be desired that this may not long remain the case. It also affords the strongest encouragement to the chemist to persevere in the search for new elements.