206 
Again, just as K, Kb, Cs, and $ = 154, are analogues of each 
other in the series Hn, so are $ = 42, $ = 96, In, and Tl, 
analogues of each other in the series H3w, and are in homo- 
logous positions with the alkaline, and alkaline earth metals 
in the series H n, and H2 n. The specific gravities of ana- 
logous members of these two series, except glucinum, 
which is anomalous, increase in the order of their atomic 
weight, and so far as the specific gravities of the members 
of the series H ?>n, have been ascertained, they follow the 
same order. Now M. Lecoq de Boisbaudran has shown that 
the new metal which he has discovered, and named gallium,* 
is, from its spectral reactions and other properties, the ana- 
logue of indium and thallium. The position of the new 
metal in the series H3?^, should therefore be either - = 42, 
homologous with Ca, and K, or - = 96, homologous with Sr, 
and Kb. In comparing the alkaline metals of the series Hn, 
the specific gravity of sodium (0*97) as will be seen, is 
greater than that of potassium (0*86), although Na has a less 
atomic weight ; and the same inversion of specific gravities 
in relation to atomic weights is observable in their homo- 
logues of position Mg., sp. g. T74, and Ca, sp. g. T58, in the 
series H2 n. It may therefore be assumed that the missing 
member $ = 42, H3 n, 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 Boisbaudran is 5 m 9;f 
and its analogues indium and thallium have specific gravities 
of 7'42, and 119 respectively, consequently $ = 42, is not 
gallium. If gallium were $ = 69 it would be the analogue 
of Y, E, and Tli, 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 Kb. There is 
then no other place for a metal having the physical proper- 
ties of gallium but the one assigned to it in the series H3n, 
* Comptes Rendus, tome lxxxi., 403, 1000, 1865, 
f Phil, Mag. 5th S., vol. ii., 398, 
