1096 



morpliotropic inflneiice of a snbslitiiciil and its atomic weiglil or 

 atomic' volume, may be supposed, is sufficiently proved by tlie 

 investigations of Mr. Tutton on the similarly constituted salts (sul- 

 phates, selenates, etc.) of the alcali-metals. Possibly it could be stated 

 that within the series of the metals of the rare earths, whose atomic 

 weights difTer from each other much less, a quantitative relation of 

 this kind would be found more easily than in the case of the 

 alcali-metals, or in that of other homologous elements of the same 

 group of the periodic system. Moreover, a more detailed investigation 

 of the molecular volumes of those crystallized salts would perhaps 

 give an opportunity to get some information about the parallelism, 

 — not yet sufficiently proved, but too many times advanced, — between 

 the changes of the atomic weights and those of the atomic or 

 molecular volumes of the lare earths or their analogous compounds. 

 Considerations of this kind are moreover closely connected with the 

 already often discussed problem, how far the element scanduun so 

 widely spread, but isolated only in small quantities and studied too 

 incompletely, must be placed among the metals of the rare earths ^); 

 finally it could in my opinion hardly be considered superfluous, to 

 compare the cry stal lographical character of the element heryUium 

 once more with that of the metals of the rare earths, in connection 

 with the doubt upon this matter, which has existed during a long 

 time with some crystallographers and chemists. ^) 



§ 3. The chpice of the ethylsulphates for these {uirposes was 

 suggested by the fact, that notwithstanding a number of tentatives 

 with other inorganic and organic acids, till now no derivatives of 

 the above mentioned oxides w^ere obtained, which at the same time 

 fulfilled tlie following conditions : 



a. To have the same number of water-molecules, if hydrated, 

 through the whole series of metals. 



h. Not to be efflorescent in dry air, jiur to be hygroscopical. 



c. To give crystals, whose faces enabled very accurate measure- 

 ments of the angles, and whose angles showed a sufficient constancy 

 with different individuals of the same salt. 



So these conditions are not fullfilled : with the beautifully crystallized 

 double nitrates of the bivalent metals Zn, Co, Ni, Mn, and Mg, 

 which always show curved and dull faces, or at least will get them 

 very fast ; nor with the platinum double-cyanides or with the 



1) G. Urbain, .lourn. de Ghim. phys. 4. 32, ^232, 321. (1906); Urbain et 

 Lacombe, Ghem. News 90. 319. (1904) ; W. Biltz, Zeits. f. anorg. Ghem 82. 

 438. (1913); R. J. Meyer, Zeits. f. anorg. Ghem. 86, 257. (1914). 



~) Debray, Ann. de Ghim. et Phys. (3). 44. 5. (1855) ; Wyrouboff, Bull, de 

 la Soc. Miner, de France, 19. 219. (1896). 



