238 C. W. R. POWELL. 
In the first of these experiments, where no manganese 
sulphate was present, the velocity increased throughout — 
the reaction and the difference between initial and final 
velocities was fairly large. As manganese sulphate was 
added the increase in the velocity throughout the reaction 
gradually lessened, until, when the concentration of man- 
ganese sulphate had reached °017 N., the velocity became 
practically constant; the difference between initial and final 
velocities being only *00001 (second order). On further 
addition of manganese sulphate the velocity no longer 
increased, and instead of showing an increase throughout 
the reaction, a slight decrease was obtained. 
This showed that the maximum efiect for the complete 
reaction was obtained when the concentration of manganese 
sulphate was ‘017N., and it is interesting to note that this 
figure represents little more than the amount of manganese 
sulphate that would have been formed by the potassium 
permanganate and sulphuric acid originally present in the 
solution. The figures in Table G. show clearly that the 
velocity of reaction is not increased on further addition of 
manganese sulphate after the concentration of this salt has 
reached 0°017 N. 
The conclusion may therefore be drawn that the acceler- 
ation obtained in those experiments in which no manganese 
sulphate is used, is due to the formation of this salt as the 
reaction proceeds, especially so since it has here been 
proved that if the amount of manganese sulphate that the 
potassium permanganate and sulphuric acid in the solution 
would finally form, be added at the commencement of the 
reaction, a fairly constant velocity of reaction is obtained. 
This power possessed by manganese sulphate to acceler- 
ate certain reactions has previously been noticed and in 
some cases its presence is necessary for the reaction to 
proceed. Harcourt? refers to the case of the oxidation of 
1 Chem. News, x, 171, 1864. 
