( 734) 
crosswise. If e.g. the red subhaloid originates after the green, the 
latter will have the power of yielding the red subhaloid, but it will 
never be possible for the green subhaloid to be photo-chemically 
formed out of the red subhaloid. This experiment already made by 
O. Wienrr?’) yields: 1s*, doubtful results, because the primary 
rendering of the spectrum already leaves much to be desired, and 
this is, consequently much more the case with the secondary rendering; 
ged, unreliable results, because in this way the chemically pure 
subhaloid is never experimented with, but by the side of it there is 
always an admixture of silver haloid. It is true, the Porrrvin process 
yields a better colour rendering, but the results are not any more 
reliable, because, as Liprpo-Cramer*') has proved, in this process 
photo-oxidation takes places by the side of photo-reduction. I, there- 
fore, selected another method. 
According to H. Lvaern **) and R. Luruer **) the photo-chemical 
decomposition of silver haloids in a closed space gets with a definite 
light intensity into a state of equilibrium owing to the halogen 
pressure which sets in. Gunrz**) determined the equilibrium pressure 
with various light intensities by exposing silver chloride under different, 
known chlorine pressures, in small glass tubes sealed in a blowpipe 
flame. This method produces decomposition in these tubes, in which 
the pressure is too small for the state of equilibrium, but is not 
suitable for determining the colour sequence, because the colour of 
the subhaloid can only be observed through that cf the halogen, 
consequently very inaccurately. Therefore it is better to proceed as 
follows. 
If silver haloid is emulsionized in a binding substance (one might 
also say: “if it is placed in a half-closed space’) the photo-chemically 
liberated halogen cannot escape immediately, but with a definite 
light intensity a halogen pressure D per unit of time will set in, 
which is dependent upon the halogen pressure D, which the photo- 
chemical decomposition process would produce, diminished in the 
first place by the pressure D, which is lost by diffusion, and in the 
second place by the pressure D, which is lost by the chemical 
combination with a halogen absorbent (chemical sensitizer). 
DED: (D, AD  e e 
In this formula D, and JD, in the second member, and consequently 
D too, may be modified. 
Now seeing that a rise of halogen pressure is accompanied by an 
increase of diffusion and of the rapidity of reaction of chemical 
combination, a fairly constant halogen pressure may continue to exist 
