472 Messrs. V. Harcourt and Esson on the [Nov. 16, 



gauic binoxide is formed according to the equation 



K 2 Mn a 8 + 3 MnS0 4 + 2 H 2 O = K 2 SO 4 + 2 H 2 S0 4 + 5 MnO a . 



3. Variation of Oxalic Acid. The results obtaiued in this series of 

 experiments are at first sight paradoxical. The quantity of permanganate 

 reduced in three minutes, which was the time allowed to each experiment, 

 increases with the proportion of oxalic acid up to a certain point ; it then 

 diminishes until another point is reached, after which further additions of 

 oxalic acid produce again a very gradual acceleration. The result is the 

 same whether only oxalic acid, potassic permanganate and manganous sul- 

 phate are taken, or whether sulphuric acid is added to these. The maxi- 

 mum action occurs with five molecules of oxalic acid and one of perman- 

 ganate, that is with proportional quantities. The second and constant 

 minimum is nearly attained with ten molecules of oxalic acid. Probably 

 the manganic binoxide formed by the reaction of manganous sulphate and 

 potassic permanganate combines with an excess of oxalic acid to form a 

 compound whose decomposition proceeds more slowly than the action of 

 free binoxide upon it. The conditions of the minimum action may be thus 

 represented : 



1. MnO 2 + 2H 2 C,0 4 =MnC 4 8 + 2H 2 0. 



2. MnC 4 O a =MnC 2 O 4 + 2CO 2 . 



There is found in the first instance a clear brown solution, the colour of 

 which slowly fades. 



4. Variation of the Time. If it were possible for all other conditions 

 of a chemical change to remain constant, if, for example, the substances 

 reacting could be added in proportion as they disappeared, and those 

 formed either were without influence or could be removed, the effect of a 

 variation of time might be confidently predicted. In such a case the total 

 amount of chemical change would be directly proportional to the duration 

 of the action. But when one or more of the substances diminishes in 

 quantity as the change proceeds, the relation is no longer of this simple cha- 

 racter. Experiments upon this relation form the remaining and chief part 

 of this inquiry. Each experiment of a series exactly resembled every other 

 except in the time allowed to elapse beforo the action was interrupted. 

 And thus each series may be regarded as exhibiting the course of a single 

 experiment, and showing how much of the active substances still remain at 

 any time from its commencement. 



In the earlier series the reagents were employed in proportional quanti- 

 ties, and it was observed that for most of the determinations the product 

 of the number expressing the duration of the action and of the number 

 expressing the amonnt of active substance still remaining, is a constant 

 quantity. The first stages of the action exhibit, however, a divergence 

 from this law. This divergence is explained by reference to the simulta- 

 neous occurrence of two gradual actions, that in which manganic binoxide 

 is formed and that in which it is reduced. The inverse proportionality of 

 the residue to the duration of the action when two substances present in 



