( 737 ) 
th part of the quantity of 3 subhaloid (which is in B), then 
the quantity of 8' subhaloid will be zero both in A’ and in C'. If 
now we further assume the same distribution in the case of the other 
subhaloids, then beginning at the point O, a series of colours will 
successively appear on the abscissa, among which there are mixed 
colours composed of at most two components between the points 
ro ie Se The equilibrium pressure at any point is then deter- 
mined by the ordinate from this point to the intersection with the 
line ABC.... Suppose that with the photo-chemical decomposition 
a constant halogen pressure D= OUP" prevails, then the state of 
decomposition will not progress beyond P’, because the equilibrium 
pressure P/P corresponding to P’ is equal to OP". Consequently 
in P’ a mixture of the p and y subhaloids will appear, the quantities 
of which are determined by the proportion Ng: VN, = P’C’: P’B’. 
A mixed colour will then appear, in which, according to the figure, 
the colour of the 3 subhaloid will be predominant. If D becomes 
greater, say D’ — OP", then the state of equilibrium will set in at 
P,’, where, according to the figure, the colour of the 2 subhaloid 
is predominant. Now by slightly modifying D between the equili- 
brium pressures of two photo-chemically consecutive subhaloids, it 
must be possible to obtain all transitional tints from one subhaloid 
to another, and this could actually be demonstrated in all those 
cases in which it was experimentally possible. 
To obtain these results, the subhaloids must, of course, be suffi- 
ciently sensitive to light. Still with a few experiments, as those with 
subiodides and subbromides, phenomena are observed which cannot 
be accounted for as yet, and require further, separate investigation. 
We shall not enter into them here. 
From the graphical representation it further appears that D can 
never become greater than the highest position of the line ABC.... 
above the abscissa. If D is smaller than the equilibrium pressure 
of the subhaloid poorest in halogen, then silver begins to separate 
out photo-chemically. 
If we assume that the line ABC... is continued still further 
towards the Y-axis, ie. that the silver haloid is placed in O before 
the @ subhaloid on the abscissa, then the ordinate belonging to it 
will correspond to the lowest halogen pressure at which the photo- 
chemical decomposition of silver haloid still takes place with this 
light intensity, and which answers to the above-mentioned chlorine 
pressure determinations by Guntz. 
Now suppose these results to be incorrect, because the continuation 
