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The silver subrhodanides. Their existence, too, is still doubtful. 
On account of its very slight sensitiveness to light silver sulpho- 
cyanide is unsuitable for these experiments. 
Results and conclusions. 
Let us now return to B. Baver’s modification theory, already 
referred to before, which owes its origin to the assumption of the 
existence of only one subhaloid, which view at one time obtained 
universally. As has been demonstrated experimentally, new colours 
only arise consecutively, if D decreases, in other words, if more 
halogen is liberated photo-chemically. Every new colour, therefore, 
belongs to a subhaloid poorer in halogen. The modification theory is 
not to be associated with this, and the assumption adopted of 
ascribing a definite absorption spectrum to each subhaloid, can still 
hold good. 
If we compare the colours series (V) and (VI), we see that even 
with the exception of the place of the yellow subhaloid, which has 
not yet been fixed with absolute certainty, they show the same 
sequence of colours, while series (IV), as far as it is known, runs 
parallel with it. If we now bear in mind that, barring slight varia- 
tions, the a-subhaloid is green, both with subiodide and subbromide 
and subchloride, we may account for the parallelism of the colour 
series by the fact that subhaloids of analogous composition have 
analogous absorption spectra. 
The colour sequence itself, too, shows regularity: the colours of 
the silver subhaloids, arranged according to the photo-chemical 
decomposition series, follow Niersxi’s rule, in which halogen behaves 
like a bathochromic group, in other words, with the decrease of the 
molecular weight of the silver subhaloids the maximum of the absorp- 
tion spectrum is shifted from red to violet. Although the structure 
formulae of the silver subhaloids are still unknown, it may be 
inferred from this that they all contain the group Ags, Hal,, which 
behaves like a chromophore or contains it. The cause of the sensi- 
tiveness to light of the silver subhaloids is, therefore, to be relegated 
to electro-magnetic light resonance. 
As according to Nietski’s rule the maximum of the absorption 
spectrum of a subhaloid still richer in halogen than the «-subhaloid 
must be situated in the infra-red, and may therefore be colourless, 
the above-mentioned experiment for the detection of this subhaloid 
by increasing D appears to be perfectly worthless. Still this does 
not alter the conclusion drawn from this experiment, that every 
