1027 
itself is oxidised as a whole is formed. At the saine time the velo- 
city of the oxidation of the sulphite beeomes less doe to the decrease 
in tlie concentration of the sulphite ions, arising out of the fonnation 
of a complex of sulphite and arsenite or of sulphite and oxalate- 
Here it seems to me that the only plausible explanation of th is 
negativo catalysis stands on the hypothesis of the fonnation of an 
intermediate complex compound. 
On investigating these varions cases of induced reactions I was 
naturally led to the more general conclusion that one Chemical 
change should induce another Chemical change ot the saine type 
and I 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 subslance (e.g. mercuric chloride) by sodium 
arsenite. I also investigated other changes, as tbr instance, the de- 
composition of unstable substances. It is well known that ammonium 
dichromate decomposes readily into nifrogen, water and chromium 
oxide. Also the deeomposition 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 
deeomposition temperature of potassium chlorate is appreciably 
lowered. In this conneclion it will be of interest to investigate 
whether the presence of an easily decomposable explosive will lower 
down the deeomposition temperature of a diffieultly decomposable 
explosive, and this in vestigation 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 eithev promote or induce 
another Chemical change of the same nature. 
A solution of ferrous ammonium sulphate is very slowly oxidised 
by atmospherie oxygen. lf 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 atmospherie 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 ammonium 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 
