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W. ScHerrER '°), every development consists in the precipitation of 
the reduction products from a dissolved silver compound upon the 
germ-subhaloid. Making use of this, in an investigation into solari- 
zation and further properties of the latent image, I'') have arrived 
at the result that the @ subhaloid of the latent image passed, with 
loss of halogen, into another, the 8 subhaloid. Soon afterwards 
B. Warrer '®), without being acquainted with my work, concluded 
from fresh investigations into solarization, that his experiments are 
best accounted for if two really different ““Zerfallstufen” (stages 
of decomposition) of silver bromide are assumed. Although, 
consequently, the existence of a number of subhaloids differing in 
chemical composition and having different properties, has been proved, 
KE. Baver’s modification theory may still be maintained by the side 
of it, for one of these subhaloids might possess the power of forming 
a modification by the action of light, through which its absorption 
spectrum might change, as e.g. white P, is transformed by light 
into orange-coloured P,;. Only if it were proved that this change of 
colour of the subhaloid was accompanied by a change in the chemical 
composition of the subhaloid, would the modification theory have to 
be relinquished. I shall revert to this question later on, and assume 
for the present that every subhaloid of a definite chemical composition 
is characterized by its absorption spectrum. 
During the last few years LüpPo-CRAMER *®), on the ground of a 
number of chemical reactions and physico-chemical phenomena, has 
drawn the conclusion that silver subhaloids, with the exception of 
subfluoride, do not exist, and are nothing but absorption compounds 
of collodial silver and silver haloid, and he has maintained the direct 
photo-chemical formation of silver from silver haloid. A short time 
ago I") succeeded in showing in a paper on silver subhaloids that 
all chemical reactions and phenomena upon which Lipro-Cramer 
founded the above-mentioned conclusion, can even be accounted for 
in a simpler way by assuming that the subhaloids are chemically 
defined compounds, so that it has not yet been proved that it is 
correct to deny the existence of silver subhaloids. K. Scnaum*®), too, 
has pointed out that the direct photo-chemical product of decompo- 
sition of silver bromide cannot be silver, for if silver bromide is 
exposed to light by the side of bright, metallic silver, Ag Br 
becomes dark, but at the same time the silver assumes a violet 
colour; “es ist thermodynamisch unmöglich, dass in dem nämlichen 
Systeme gleichzeitig AgBr in Ag und Ag in AgBr iibergeht”. Hereby 
it was proved, not only that the conception of the silver subhaloid 
as an absorption compound, was untenable, but also that the formula 
