298 The Chemistry of the Future. [July, 
solutions. In faCt, the properties of the hypothetical metal 
ought to ‘ present the mean between those of aluminium 
and indium,’ metals whose oxides are almost completely in- 
soluble in ammonia.” Yet in a footnote he very materially 
qualifies this deliverance. He there states — “ Oxide of 
indium is generally considered almost insoluble in ammonia, 
a property which is utilised in its separation. As for alumina, 
its solubility in ammonia, though slight, is sensible. It re- 
mains to be seen whether the great delicacy of the speCtral 
reaction of gallium, and the minuteness of the quantities 
upon which I have operated, may not have caused me to 
over-rate the relative insolubility of gallic oxide in ammonia.” 
We cannot here help pointing out that the solubility of hy- 
drated alumina in ammonia is sufficiently great to vitiate an 
analysis, even for technological purposes, unless certain 
well-known precautions are observed. Hence gallia may 
still be taken up by ammonia to an extent amply sufficient 
for spectroscopic purposes, even if considerably less soluble 
in that medium than is alumina. 
M. Lecoq de Boisbaudran further observes that without 
the particular method followed in the present investigation 
neither the theories of M. Mendeleeff nor his own would 
have, for a long time, led to the discovery of gallium. 
With all due deference we must submit that this point is 
utterly beside the question. If certain theories enable us 
to foretell correCtly the properties of a metal as yet undis- 
covered, their value is established, and whether the ultimate 
discovery of such metal was due to the prediction is a mere 
secondary consideration. 
M. Mendeleeff has also announced the probable existence 
of another metal, to which he gives the name of “ eka- 
silicium,” Es = 72, forming an oxide Es 0 2 . Its properties 
ought to be intermediate between those of silicium and tin, 
and it is to be especially sought for among arseniferous and 
titaniferous minerals or residues. To the discovery of this 
metal — if metal it may be called, since even tin is relegated 
among the non-metallic bodies by chemists whose opinions 
are entitled to respeCt — we must look forward with anxious 
interest, not so much for its own sake as for the light which 
it must throw upon the theory in question. 
We must now proceed to an exposition of the law which, 
in one instance at least, we have seen so signally verified. 
M. Mendeleeff sets out with a brief reference to the labours 
of those chemists who have preceded him in this line of 
enquiry. Gladstone, Cooke, Dumas, Pettenkofer, have all 
pointed out that the atomic weights of certain groups of the 
