BETWEEN THE CONDITIONS OF A CHEMICAL CHANGE AND ITS AMOUNT. 195 



of potassic iodide, by which the remaining permanganate is instantaneously reduced. The 

 amount of iodine set free, which had previously been proved to furnish an exact measure 

 of the permanganate, was finally determined by means of a standard solution of sodie 

 hyposulphite. 



Table I. 



K2Mn2 08+5H2C2 04+2MnS04+a^H2S04. 



Volume of solution 330 cub. centims. Temperature 16° C. Time 4 mins. 



When no oxalic acid was taken and the whole amount of permanganate was repre- 

 sented by its equivalent of iodine, there were used to decolorize the solution 36-3 cub. 

 centims. of hyposulphite. 



The numbers in column 3 are obtained by making this number 100, and reducing 

 the mean of those in column 2 to the same scale. It will be seen that the amount of 

 chemical change occurring within the allotted time increases continually with the 

 quantity of sulphuric acid in the solution, the effect, however, of successive increments 

 being less and less. This relation is exhibited by the annexed curve (Plate XVII. fig. 1). 

 In spite of the apparent simplicity of the conditions of these experiments and of the 

 progressive variation introduced, no simple relation could be discovered between the 

 two series of numbers. It vdll be shown subsequently, by the light of later experi- 

 ments, that the relation between them is of a very complex character. Two molecules 

 of manganous sulphate were added to the mixture, that the rate might not be disturbed 

 by its gradual formation. The part played by this salt appearing particularly worthy 

 of investigation, was made the subject of the next series of experiments. 



B. Variation of Sulphate of Manganese. 



All the conditions adopted in the first series were repeated in this, with the exception 

 that ten molecules of sulphuric acid were used in each experiment, and the amount of 

 manganous sulphate was varied. 



2 E 2 



