REVERSIBLE AND IRREVERSIBLE SYSTEMS UNDER INFLUENCE OF LIGHT. 385 
an increase by (R0072 per cent, to 0 - 22 per cent. If the solution pressure of an 
electrode in the dark is known, the solution pressure in light, under any given 
condition, is also known. Putting P d for Ag = 10~ 15 atmosphere, the solution pressure 
of Ag plates becomes in light in the investigated systems 
PZ = (P00072 to P0022) 1CT 15 atmosphere. 
(6) § 7, I., II., VIII., XV., as well as Table I., § 6, show that in constant reversible 
cells the E. M.F. created by light, and with it approximately the heat of reaction, are 
directly proportional to the intensity of light, i.e., 2E = Cl ; p" — C'l, and since 
the same holds good for plates absorbing the total light (CuO in NaOH) and for 
plates absorbing only a part of it (Ag plates in N0 3 Ag), the same law of intensity 
holds good (at any rate approximately) for the absorbed, as well as for the reflected 
light. Experiments of July 29, 1903, Plate N13, Table III., carried out with pure 
red light, and § 7, VIII., with blue light, show that the same law of intensity holds 
good for monochromatic light as well. 
§ 9. The Results obtained for Chemical Statics and Dynamics under the Action 
of Light , in General. 
(a) Further Experimental Proof that Velocity of Chemical Reaction in Homogeneous 
Systems when they are shifted to a New Point of Equilibrium by Light at 
a Constant Temperature, and Chemical Equilibrium of Homogeneous Systems, 
follow the Laws of Mass Action as in the Dark. 
The above laws which I found experimentally to regulate, after the induction period 
has passed, those regions of phenomena under the action of light (see ‘ Roy. Soc. 
Proc.,’ January, 1902; ‘Phil. Trans.,’ A, 1902, vol. 199, p. 337 ; ‘ Zeitschr. fur physik. 
Chemie,’ June and December, 1902; ‘Phil. Mag.,’ January, 1903) now find further 
extensive experimental confirmation in the “ galvanic cells created by light ” as is 
evident from (c). 
Having shown here that the chemical potential of the same plate is in light 
different from that in the dark, the proof is thus given that the thermodynamic 
deduction of the same laws of mass action (after the induction period) given in the 
above papers is a mathematical necessity. 
Since the publication of the papers above mentioned, a series of efforts have been 
made by different persons to investigate velocity of reaction, or velocity of reaction 
and equilibrium under the action of light, but with little success (see Guldberg, 
‘ Zeitschr. physik. Chemie,’ 41, 1902 ; Slator, ‘ Zeitschr. physik. Chemie,’ 45, 
p. 540, 1903; P. Bevan, ‘Phil. Trans.,’ A, 1904; Luther and Weigert, ‘Sitz. K. 
Preuss. Akad.,’ 1904, p. 828). 
No reference was made in the above publications to my work. The cause of 
vol. ccvi.— a. 3 D 
