86 
appeared to diminish gradually with inereasing concentration of the 
catalyst; and 3. the tendency of cobalto-oxalate to form supersa- 
turated solutions *), instead of precipitating normally. Finally there 
is again a disturbing effect, because of the subsequent photochemical 
decomposition of the ovalate-ion and its transformation into a for- 
mate-ion, which reaction, as BerrHeror and GAUDECHON ”) had already 
demonstrated formerly, oecurs chiefly under the influence of rays of 
small wave-lengths. All the different effects mentioned manifest their 
special influence in a more or less sensible degree, and they prove 
sufficiently, how very complicated indeed the whole mechanism of the 
process is. 
The author could, however, not find a catalysing action by 
addition of acids, such as hydrochloric or sulphuric, under the 
conditions of his experiments *). 
$ 3. In contrast to those of VraNek, our experiments were 
executed with much more concentrated solutions of the complex salt, 
while, after many trials, finally the direct gravimetric determination 
of the cobalto-oralate generated was adopted as method of analysis; 
the cobalto-salt was determined as metallic cobalt, after reduction in 
a current of dry hydrogen. Even in the case of very concentrated 
solutions, the error resulting from the solubility of the precipitate 
in the solution containing potassium-ovalate, appeared to be small 
enough to neglect it in comparison with the other incertitudes of 
the experiment: in the most unfavourable circumstances the deviations 
caused by this factor did not surpass 1,5 °/,. 
The dark green liquid was kept in a vessel of transparent quartz, 
surrounded by a quartz-mantle of greater diameter; in the space 
between the cylinders a current of water was continually passed, 
which was kept at an almost constant temperature by means of a 
metallic spiral-tube, placed in a thermostat; the temperature varied 
in our experiments between 21° and 23° C. As source of light a 
quartz-lamp (HERAKUS) was used, which was placed always at ex- 
actly the same distance (140 m.m.), and which sent its rays into 
the solution not before its current had reached a constant and 
always identical intensity, and also its radiating power had become 
constant. All the conditions of the experiments were, for the rest, 
in all cases as constant as possible; e.g. the volume of the 
solution was always the same, namely 50 ccm. Because also the 
1) Sr. Deakin, M. Scorr and B. D. SreeLe, Zeits. f. phys. Ghemie, 69, 126, (1909). 
2) D. BerrHeLot and H. GAUDECHON, Compt. rend. de l'Acad. d. Sc. Paris 
152, 162, (1911). 
3) J. VRANEK, loco cit, p. 350, 
