960 REPORT—1885. 
hardly be the case if the valency of the iron were increased ; and that in like manner 
the compounds formed from stannous chloride manifest all the properties of 
stannous derivatives. 
Whatever be the nature of chemical affinity, it is difficult to resist the conclusion 
that the ‘charge’ of a negative radical especially is rarely, if ever, given up all at 
once ; that its affinity is at once exhausted. It would also appear that the amount 
of residual charge—of surplus affinity—possessed by a radical after combination 
with others depends both on its own nature and that of the radical or radicals 
with which it becomes associated. Differences such as are observed in the com- 
position and stability of the hydrates of the salts of an acid—the sulphates, for- 
example—clearly point to this. Other illustrations are afforded by the manner in 
which chlorhydric acid yields chlorhydrates of some metals and chlorides of others.! 
It is noteworthy, however, that often those elements which from the ordinary 
point of view are regarded as possessed of feeble affinities are those which manifest 
the greatest tendency to form molecular compounds. Thus, it is commonly held’ 
that, of the three elements, chlorine, bromine and iodine, chlorine has the highest 
and iodine the lowest affinity, and this view accords well with the recent observa- 
tions of V. Meyer on the relative stability of their diatomic molecules at high 
temperatures ; but nevertheless we find that the compound which HI forms with 
PH, is far more stable than that of HBr or HCl with this gas; and it is well 
known that mercuric todide has a much greater affinity for other iodides than have: 
mercuric bromide and chloride for the corresponding bromides and chlorides.” 
The recognition of the peculiarity in the negative elements to which I would 
attribute the formation of molecular compounds must, I think, exercise an important 
influence in stimulating and directing the investigation of these compounds and of 
compounds other than those of carbon; in the near future the determination of 
the structure of such compounds should occupy an important share of the chemist’s 
attention. It will perhaps afford a clue in not a few cases which are not altogether 
satisfactorily interpreted in accordance with the popular view of valency. I may 
instance the formation of (?) polymeric metaphosphates, of complex series of silicates 
and tungstates, and of compounds of hydrocarbons with trinitrophenol. It may 
even serve to explain some of the peculiarities of the more complex carbohydrates. 
It is one of the most clearly established of the ‘laws of substitution’ in 
carbon compounds that negative radicals tend to accumulate: numerous instances: 
are afforded by the behaviour of paraftinoid compounds with chlorine, bromine and 
oxidising agents, and by that of unsaturated paraftinoid compounds when combining 
with hydrogen bromide and iodide. The special affinity of negative elements for 
negative is not improbably the cause of this accumulation. A similar explanation 
may perhaps be given of some of the peculiarities which are manifested by 
benzenoid compounds. ‘ 
I would even venture to suggest that in electrolysing solutions the friction 
arising from the attraction of the ions for each other is perhaps diminished, not by 
' The name chlorhydric acid is here applied to the compound HC1(OH,)x—pro- 
bably x = 1—which, according to Thomsen, is present in an aqueous solution of hy- 
drogen chloride. It would be an advantage if we ceased to speak of HF, HCl, HBr, 
HI, as acids, and always termed them hydrogen fluoride, chloride, bromide and iodide 
respectively. The names hydric chloride, bromide, &c., might with equal advantage 
be altogether abandoned ; hydrochloric acid is objectionable, as suggesting a relation 
to chloric acid. The names fluor-, chlor-, brom- and iodhydric, as applied to the 
acids present in aqueous solutions of the hydrides, are especially appropriate as indi- 
cating that they are compounds containing the radical water—that they are hydrates : 
indeed, it would be well to restrict the use of hydric and hydro- to bodies of this 
kind, and to speak of hydrides as hydri-, not as hydro-, derivatives. It would then 
be possible to give comparatively simple names even to complex hydrates. 
* Thomsen gives the values in heat units as— 
HgCl,,2KClAq = ~—1380 
HgBr,,2KBrAq = 1640 
Hgl,,2KIAq = 3450 
HgCy,,2KCyAq= 8830 
