132 MR. H. WILDE ON THE 



H2?i. It may therefore be assumed that the missing 

 member .2? = 42, H3W, would have a less specific gravity 

 than Al (sp. g. 2'56), probably 2-5. Now^ the specific 

 gravity of gallium^ as determined by M. Lecoq de Boisbau- 

 dran^ is 5*9 '^, and its analogues indium and thallium have 

 specific gravities of 7*42 and 11 "9 respectively, conse- 

 quently ^=42 is not gallium. If gallium were x = 6c) it 

 would be the analogue of Yt^ E, and Th, and homologous 

 in position with Zn and Cu, whereas it has been shown to 

 be the analogue of In and Tl, and homologous in position 

 with Sr and Rb. There is then no other place for a metal 

 having the physical properties of gallium but the one 

 assigned to it in the series H^^, with the atomic weight 

 = 96, and forming a triad with indium and thallium. If, 

 however, the experimental determination of the atomicity 

 of gallium pass through the same stages as the atomicities 

 of indium, yttrium, and other members of the series, its 

 atomic weight will be represented by the submultiple and 

 proportional numbers 48 and 72 f. 



Just as silver and copper are analogues of each other, 

 and are frequently associated in nature ; and just as their 

 homologues, cadmium and zinc, are analogues, and are 

 also found together, so is yttrium the analogue of ^ = 69, 

 and will be found associated with it in nature. Now, if 

 a;=6g be not the terbium of Mosander and Delafontaine, 

 and the researches of Bahr and Bunsen render the existence 

 of this element doubtful, it is probable that a^=.6g is 



* Phil. Mag. 5tli ser. vol. ii. p. 398. 



t From a calcination of the gallo-ammoniacal alum, M. Lecoq de Bois- 

 baiiclran has recently found for gallium the equivalent 70*03, and from a 

 calcination of the nitrate, 6g-6. — Comptes Sendtis, A-pvil 15th, 1878. The 

 researches of M. Berthelot on the specific heat of gallium indicate, however, 

 a higher equivalent for the metal than 70-03, as the atomic heat calculated 

 from this determination (5"55 solid) is lower than that of any other metal 

 except silicium. — Ibid. April 15th, 1878. 



