87 
crystallised complex salt is decomposed very slowly, when preserved 
in darkness, the preparation used in our first experiments contained 
a very small quantity of the cobalto-salt; so that, after its quantity 
had been determined accurately, the necessary, and only very small 
correction of the results made necessary by it, was applied in the 
first series of measurements. The degree of accuracy of the method 
of analysis was tested beforehand by experiments with mixed solutions 
of known composition, and it was found really sufficiently great. 
The solutions were continually stirred by means of a current of 
nitrogen, regulated at about four bubbles every second ; later-on stirring 
was brought about by a current of carbon diowide, after it was found, 
that the reaction was not influenced by it in any respect. It is necessary 
to perform the analysis of the solutions in darkness, and to filter 
the precipitate as rapidly as possible, to wash it immediately, and 
to carry out all necessary manipulations in rapid succession. As long 
as the mother-liquor is adhering to the precipitate, all access of 
light must be carefully prevented, as well as all considerable increase 
of temperature. . 
In a first series of determinations, we thus obtained the following data: 
eee pd 
minutes: | in 50 ccm: | found: decomposed: 
223 | 60 ‘| 0.7247 Gr: 0. 0634 Gr. 73.349, 
22.2 60 | _0.9709 0. 0665 Bl.4l | 
Bae ee gy oN. d.2124 0. 0695 | 48.05 | 
ee 60s | 1, 4655 0, 9694 | 39.70 | 
21.7 60 1. 7021 0. 0686 | 38.78 | 
21.9 60 1. 9434 0. 0699 | 30. 16 
Taking into account the unavoidable uncertainties, which always 
remain in the study of so highly complicated a reaction as this, 
and attributing only a moderate value to the small increase which 
the first four numbers apparently show with respect to each other, — 
it must be evident from these results, that the quantities of the 
salt decomposed within identical intervals of time are approximately 
independent of the initial concentration, and chiefly determined by 
the amount of light-energy absorbed during that time. The reaction- 
order is evidently zero, — a fact which may be used as an argument 
on behalf of the view, that the process is of a purely photocatalytic 
