93 
But all curves of Fig. 1 manifest a clear and obvious analogy of 
shape: they rise evidently all to a steeper or flatter maximum, 
and then decline more or less rapidly. The addition of all these 
electrolytes thus involves an acceleration of the photochemical 
reaction in the case of smaller concentrations of them, which, 
however, reaches a maaimum at a certain concentration, charac- 
teristic of each salt, and which subsequently again diminishes. 
In some cases this diminution may even change into a retardation 
of the process') at concentrations, which are not even so very high ; 
and finally in the case of MgCl,, for instance, the reaction may 
be stopped even completely by it! 
Another very remarkable fact is, that the maxima are situated at 
smaller concentrations, as the valency of the cation, te. its electrostatic 
charge, is greater: for the divalent My-ion this maximum approaches 
much nearer to the ordinate-axis, than for the monovalent ions of 
the. alkali-metals, while the maximum of the curve of the trivalent 
Fe-ion is situated in the immediate vicinity of the Y-axis. The nearer 
these maxima approach the ordinate-axis, the more steeply the 
curves will appear to decline after passing the maximum. However, 
not only the electric charges of the ions, but also their specific 
properties appear to play a part in this: thus, for instance, the 
three maxima of the curves of the alkali-metals do not coincide, 
although their charges are the same; but they approach the Y-axis 
the more closely, the smaller is the atomic weight of these elements. 
The respective concentrations of the solutions of these three electro- 
lytes, at which the maxima are reached, are, if graphically inter- 
polated, — for LiCl, NaCl, and KCl respectively: 1,65 N. equiv., 
1,88 N. equiv, and 1,96 N. equiv.; these concentrations may e.g. 
be considered as approximatively proportional (1: 1,14: 1,18) to the 
logarithms of the ionic velocities at 18° C. of the three kinds of ions, 
being here about: 1: 1,06: 1,17. Of course, we emphasize, that no 
especial significance should be attributed to such relations as suggested 
here, because the number of data is yet too small, and their accuracy 
not sufficiently great. But attention may be drawn to the fact only 
that the specific properties of the ions play also a rôle in this, and 
1) It may be remarked here, that Jorissen and REICHER (loco cit), as well 
as Rororr, found instances of positive and negative photocatalysis under the 
influence of neutral salts, however, without making a general supposition about 
the possible shape of the respective curves. In ROLOFF’s paper one case is mene 
tioned, which is in full agreement with the data obtained by us, namely, where he 
used ANO, as a catalyst, and found a maximum of its action at a certain con- 
centration. 
