48& Dr. Grore on the Greater Influence of First Quantities 



Fig. 3. 

 HN0 3 -63 grain, with CdPt at 21° C. 



On examining these curves, the greater effect of the first 

 unit quantity of water added to the acid than the succeeding 

 ones is distinctly visible in each case. On comparing them 

 with those obtained by adding unit quantities of the same 

 acids to water (Phil. Mag. May 1890, p. 421), we find that 

 the greater effects of the first added unit quantities of acid 

 were much more conspicuous than those of the first added 

 unit quantities of water ; and that whilst the first quantities 

 of acids added to water increased the electromotive force, the 

 first quantities of water added to acids decreased it. The less 

 conspicuous effects produced by adding water to acids than 

 by acids to water, were probably due to the circumstance that 

 the acids had each been already largely diluted, about 30 to 

 50 times their weight, before adding the first units of water 

 to them. In confirmation of this statement, I have found 

 by experimental measurements that both with hydrochloric 

 and with sulphuric acid the greater influence of the first added 

 unit of water was more conspicuous when the acids were less 

 diluted beforehand. 



The results obtained with these three acids indicate that the 

 greater influence of the first added unit quantity of water is 

 not limited to water added to absolute acid, but extends to 

 that added to acid already considerably diluted, and therefore 

 the property under consideration is a more general one. 



I have similarly examined the effect of adding successive 

 unit quantities of water to a saturated aqueous solution of 

 potassium chloride, containing 25'0 grains of the salt in 77*5 

 grains of water, upon the electromotive force of a zinc- 

 platinum couple. The annexed curve shows the results :— 



