212 MESSES, A. V. HAECOURT AND W. ESSON ON THE LAWS OF CONNEXION 

 hence 





but if dy is the whole amount of binoxide which disappears in the time dx, we have 



dy=d^-\-d^-\-...-\-d„y, 

 <and therefore 



J= -(«, + «,+ ... +a„)y, 



or 



a logarithmic curve of the same type as that obtained in the case in which only one 

 product is formed. 



But since the proportions of the reagents and all other conditions of the reaction have 

 been kept rigorously constant, we may presume that between any two reagents only one 

 reaction occurs. If, therefore, oxalic acid yields both the normal products of its oxida- 

 dation, carbonic acid and water, and also the substance, whatever it may be, which acts 

 slowly on hydriodic acid, it is probable that it is oxidized by more than one reagent. 

 The following experiments supply some further evidence that oxalic acid may hold dis- 

 solved two distinct manganic oxides, and be attacked by them at different rates ; or — 

 if, as we have supposed, solution here is due to combination — that two manganic oxalates 

 may be formed whose rates of decomposition are different. 



A solution was prepared of manganous-manganic sulphate by dissolving a quantity of 

 manganous sulphate in dilute sulphuric acid, and saturating the liquid with hydrated 

 manganic binoxide. The brown precipitate dissolves slowly and sparingly, forming a 

 deep-red solution, which is completely decomposed by the addition of a sufficient quan- 

 tity of water. A second solution was made of potassic permanganate of equal oxidizing 

 power when measured by hydriodic acid. The rate at which each was reduced by oxalic 

 acid in presence of equal quantities of manganous sulphate and sulphuric acid was deter- 

 mined, and the two rates found to be very nearly the same. A third series of determinations 

 was made under the same conditions, excepting that no manganous sulphate was taken, 

 with hydrated binoxide of manganese suspended in so much water as made a measure 

 of it equivalent to a measure of the former solutions. For half a minute, until the 

 binoxide was dissolved, the action took place rapidly ; but when the liquid became clear, 

 it proceeded more slowly for an equal amount of oxidizing residue than in the other 

 solutions. This solution, therefore, differs from the former, which so far resemble one 

 another, both in appearance and in rate of decomposition, as to render it likely that the 

 chief agent is in both cases the same. 



The direct action of permanganic acid on oxalic acid at a temperature of 16° or 17° is 

 very gradual ; perhaps if every trace of lower oxides of manganese and of other reducing 

 agents than oxalic acid could be excluded, no action whatever would take place. But 

 whether this be so or not, it may certainly be disregarded in comparison with the almost 



