1078 
itself is oxidised as a whole is formed. At the same time the velo- 
city of the oxidation of the sulphite becomes less due to the decrease 
in the concentration of the sulphite ions, arising out of the formation 
of a complex of sulphite and arsenite or of sulpbite and oxalate. 
Here it seems to me that the only plausible explanation of this 
negative catalysis stands on the hypothesis of the formation of an 
intermediate complex compound. 
On investigating these various cases of induced reactions I was 
naturally led to the more general conclusion that one chemical 
change should) induce another chemical change of the same type 
and 1 tried to verify this conclusion. I found that the reduction of 
mercuric chloride by such different reducing agents as formic acid, 
sulphurous acid, phosphorous acid etc. induce in all cases the 
reduction of the same substance (e.g. mercuric chloride) by sodium 
arsenite. I also investigated other changes, as for instance, the de- 
composition of unstable substances. If is well known that ammonium 
dichromate decomposes readily into nitrogen, water and chromium 
oxide. Also the decomposition temperature of potassium persulphate 
is lower than that of potassium, chlorate, and I have found that in 
presence of decomposing ammonium dichromate or persulphate the 
decomposition temperature of potassium chlorate is appreciably 
lowered. In this connection it will be of interest to investigate 
whether the presence of an easily decomposable explosive will lower 
down the decomposition temperature of a difficultly decomposable 
explosive, and this investigation will throw light on the stability of 
mixed explosives. As far as my experiments go I am inclined to 
the view that one chemical change will either promote or induce 
another chemical change of the same nature. 
A solution of ferrous ammonium sulphate is very slowly oxidised 
by atmospheric oxygen. If an oxalate is added to this solution the 
rate of oxidation is greatly increased, and the ferrous iron readily 
passes into the ferric state in presence of atmospheric oxygen, and 
the oxalate is also slowly oxidised. The same sort of behaviour is 
noticeable if we add a tartrate or a citrate instead of an oxalate 
to a ferrous salt solution. The potential reducing activity of iron is 
increased by the addition of an oxalate or a tartrate. Hence soluti- 
ons of ammoniuw ferro-oxalate, or ferro-citrate or ferro-tartrate are 
better reducing agents than ferrous ammonium sulphate and are 
largely used as developers in photography. 
Now there is no chemical change between potassium oxalate and 
mercuric chloride in the dark at the ordinary temperature, though 
the following chemical change takes place in light 
