Scheikunde. — De Heer Ernst Cohen biedt eene mededeeling aan 
van den Heer Nil Ratan Dhar: “Catalysis — Part XII. 
Some induced reactions and their mechanism” . 
(Mede aangeboden door den Heer van Romburgh). 
Wlien an aqneous solution of mercuric chloride is boiled with 
oxalic acid, tliere is no rednction of the mercuric chloride to the 
mercurous state, but as is vvell known this mixture of mercuric 
chloride and oxalic acid decomposes at the ordinary temperature in 
sunlight according to the equation, 
2HgCl, + H,C,0 4 = 2HgCl + 2HC1 -f 200,. 
The same change, however, takes place in the dark as the au t hor 
has observed if a few drops of a deci-normal potasssium permangan- 
ate are added to the mixture. As soon as the color of the per- 
manganate is discharged, mercurous chloride begins to separate out. 
This phenomenon appears to be of general occurrence. Thus the 
reduction of mercuric chloride and bromide by oxalic acid, tartaric 
acid, citric acid, malonic acid, malie acid, glycollic acid, cane sugar, 
glycerine, lactic acid, hydroxylamine hydrochloride, hydrazinehydro- 
chloride etc., the reduction of gold chloride by several reducing 
agente, the reduction of silver nitrate, cupric chloride and selenious 
acid (to selenium) by various organic acids, cane sugar etc. are 
promoted by the addition of such oxidieing agents as potassium 
permanganate, potassium persulphate, manganese dioxide, potassium 
uitrite, hydrogen peroxide, ceric salts etc. 
It is a remarkable fact that this effect is particularly noticeable 
in tliose reaction6 which are sensitive to light. 
In all these instances, Chemical changes are taking place in a 
homogeneous system. I have also investigated several cases of induced 
reactions taking place in heterogeneous Systems, and I have made 
a special study of oxidations effected by oxygen of the air. The 
following are some of the experimental results obtained: 
66 * 
