BETWEEN THE CONDITIONS OP A CHEMICAL CHANGE AND ITS AMOUNT. 199 



even of a sixth molecule ; but the increase is no longer in direct proportion, but in a 

 less ratio. The explanation already suggested appears to be in accordance with all the 

 phenomena both of this and of the first series. The rate at which a given amount of 

 oxalic acid is oxidized diminishes as the total amount present increases up to that point 

 at which enough has been added to convert the potassic permanganate and manganous 

 sulphate into oxalate of manganic binoxide and a potassium salt. With one molecule 

 the rate at which its oxidation proceeds is very great, but when it is complete, the per- 

 centage of chemical change cannot exceed twenty. Accordingly it attains this limit in 

 the second series, and nearly approaches it in the first. With two molecules the rate is 

 less, and still less with three, but the proportion oxidized in any time is a less propor- 

 tion of a larger quantity. When five molecules have been added, the total amount of 

 chemical change possible cannot be increased, since this quantity is sufficient to reduce 

 the whole of the permanganate. Consequently the amount oxidized in any time is 

 thenceforward a less proportion of the same quantity. The annexed diagram, in 

 which the course of each experiment is represented by a separate curve having for 

 its asymptote a line parallel to the axis of a^ at a distance representing the total 

 amount of chemical change possible after the lapse of any length of time, may serve 

 for illustration. 



X = time ; y = percentage of chemical change ; Cj, C,, ... C,, curves representing 

 the action with 1, 2, ... 12 molecules of oxalic acid. 



