BETWEEN THE CONDITIONS OF A CHEMICAL CHANGE AND ITS AMOUNT. 201 



ganate, 0-014 grm. in 10 cub. centims. of water, was added and rapidly mixed with 

 the rest. The moment of its addition was noted, and when the proper interval had 

 elapsed an excess of potassic iodide was thrown in. The amount of iodine liberated was 

 then determined. 



Table V. 



K2Mn2 08+3MnS04+6H2S04+5H2C2 04. 



Volume of solution 330 cub. centims. Temp. 16° C. Time x mins. 



This series of determinations may be regarded as exhibiting the course of a single 

 experiment in which the reaction is allowed to proceed during seventeen minutes. Of 

 a hundred parts of the oxidizing and reducing substances (or transferable oxygen, or 

 chemical energy) originally present, there remain after one minute 95*6 parts, after 

 two minutes 83-2 parts, and so on. Throughout the middle part of the course of this 

 experiment, from the end of the fourth to the end at any rate of the tenth minute of its 

 progress, a relation exists between the corresponding numbers in the first and second 

 columns which strikes the eye at once. Their product is a constant quantity. The 

 divergence of the results for the fifteenth and seventeenth minutes is probably due to an 

 experimental error, committed either in determining the rather small amount of residue, 

 or in the measurement of the proportional quantities of the two principal reagents ; such 

 an error would affect chiefly the later stages of the experiment, the ratio of the two 

 substances which should be constant changing slowly at first and afterwards more rapidly. 

 But the divergence of the result in the earlier part of the experiment is much more 

 considerable, and shows unmistakeably that, until the reaction has advanced a certain 

 distance, it does not follow the hyperbola which correctly represents the remauider of its 

 course. The same fact, it wUl be seen, reappears in every similar series of experiments. 

 Its cause was for a long time obscure, and the authors were driven to discard this rela- 

 tion, which appeared only to hold good for part of their results, and to be inconsistent 

 with others of equal authority. Later experiments, however, have established the reality 

 of this relation, and led to the discovery of the cause of divergence. 



MDCCCLXVI. 2 p 



