Scheikunde. — De Heer Ernst Cohen biedt, eene mededeeling aan 
van den Heer Nil Ratan Dhar : „Catalysis” — Part VII — 
Notes on Catalysis in lieterogeneous systcms. 
(Mede aangeboden door den Heer van Romburgh). 
1. It is known for a long time that violet chromic chloride is 
practically insolnble in water, biit in presence of redncing agents 
solution takes place diie to the transformation into the solnble 
inoditication. 
Anhydrons ferric sulphate dissolves slowiy in water at the ordi- 
narj' temperatnre, in other words, it may be said to have a sraall 
velocity of solution. 1 have found that redncing agents like stannoiis 
chloride, ferrous sulphate, siilphnrous acid etc., inarkedly accelerate 
the velocity of solution of ferric sulphate in water. 
In the case of chromic chloride, it is assumed that the redncing 
agent first reduces the insolnble chromic chloride to chromous 
chloride, and the original chromous chloride is transformed into 
solnble chromic chloride. The newly formed chromous chloride then 
acts on the insoluble chromic chloride as before. 
The difliculty of an explanation like this is that we assume that the 
reducing agent acts on the solid chromic chloride and reduces it; 
from our experience in heterogeneous Systems, we know how diffi- 
cult it is to reduce a solid substance rapidly with a solution of a 
reducing agent. 
Moreover, in the case of fei'ric sulphate we do not know two 
varieties of the salt as in the case of chromic chloride. 
It is difïicult to assume that ferrous sulphate would reduce ferric 
sulphate, for we know that a mixture of ferric and ferrous salts 
can exist unchanged for an indefinite period in absence of oxygen. 
So we can say with Ostwald (Grnndlinien der anorganischen 
Chemie, Leipzig 1900; A. Findlay’s trans. 603, 1902) that a sufficiënt 
explanation of these actions is still wanting. 
2. The action of nitric acid on the metals generally, is somewhat 
complex, because the main reaction is cornplicated by side or con- 
current, and by consecutive reactions. These again depend not only 
upon the particular metal under consideration but also on the 
36 
Verslagen der Afdeeling Naluurk. Dl. XXVIll. 1919/20. 
