( 735 ) 
for a definite period during the decomposition, if the chemical 
sensitizer is present in not too small a quantity. (Compare the result 
of the experimental inquiry into the influence of the size of the grain 
upon JD, below, with the accuracy of this reasoning). Practically it 
is not even so very simple to take too small a quantity of chemical 
sensitizer, because the first visible decomposition of the silver haloid 
already sets in, when a quantity of halogen, too small to be weighed, 
has been photo-chemically liberated, which is undoubtedly owing to 
the intense colour of the subhaloids. 
The cause of the more rapid photo-chemical decomposition of silver 
haloid in the presence of a chemical sensitizer has been attributed 
by Guntz**) to the development of heat, which accompanies the 
chemical combination of the lberated halogen, because this photo- 
chemical decomposition is attended with heat absorption. If this 
cause really had such a great influence upon the decomposition 
process, formula (III) would have to be considerably modified. This, 
however, is not the case. LürPo-CRAMER **) has demonstrated experi- 
mentally that the chemical sensitizer only accelerates the decomposition 
process, if the silver haloid is emulsionized. Silver haloid precipitated 
in a test tube does not show a trace of accelerated photo-chemical 
decomposition, neither by the addition of silver nitrate, nor by the 
addition of ammonia. I must, however, observe that the colours which 
appear are not the same. Consequently the thermic influence of the 
chemical sensitizer, referred to by Guntz, is so small that in practice 
it may be ignored, and may at most be taken as a theoretical correc- 
tion of formula (III), especially if it is borne in mind that the total 
amount of halogen that is liberated and reacts in my experiments, 
is extremely small. 
On the analogy of the more or less regular changes of properties 
in the case of other chemical series, as e.g. the fatty acids, it may 
be assumed that the subhaloids according to series (II) will show 
an increased or decreased affinity, however small the differences 
may be mutually. As with a constant light intensity the photo- 
chemical decomposition of the subhaloid gets, at a certain definite 
halogen pressure, into a state of equilibrium, we may say that the 
equilibrium pressure in the ease of the subhaloids according to series 
(II) undergoes an increase or a decrease. Even the measurements of 
EB. Baver °°) mentioned before, who observed a rise of the potential 
with a higher proportion of halogen, point to the fact that with a 
constant light intensity this equilibrium pressure will decrease if the 
amount of halogen in the subhaloids is smaller. 
If now formula (III), in which, consequently, D is practically 
50* 
