288 Dr. C. R. A. Wright on the Determination of 



whilst with stronger solutions the difference is yet more 

 marked. 



112. A number of analogous observations were made with 

 cells containing dilute sulphuric-acid and copper-sulphate 

 solutions, not both of the same specific gravity: the average 

 results were as follows:— 



Specific gravity of Excess of spe-JP^^ ! 



solutions. cific gravity of , I Average 



xcess 01 spe- E M F 



cine gravity 



of copper 



Acid. 



copper sul- 

 ri phate over 



C °PP er iacid solution, 



observed. 



sulphate. 



sulphate. 



Observed E.M.F 

 corrected for 



excess of specific; 



gravity of cop 

 per sulphate. 



1-010 1-050 

 1-010 1-090 

 1010 1-175 



+ 040 

 + •080 

 +•165 



-0-008 

 -0-015 



-0-019 



1147 

 1-135 

 1-137 



Average. 



1-139 

 1-120 

 1-118 



1126 



1050 



1-175 



+•125 



-0012 



1-148 



1-136 



1-175 1-050 

 1175 1-090 



-•125 

 -•085 



+0-012 

 +0008 



1-168 

 1-164 



Average., 



1-180 

 1-170 



= 1-175 



The final averages representing the E.M.F. corrected to 

 the uniform specific gravities 1*010, 1*050, and 1*175 respec- 

 tively, do not differ from the values directly obtained as just 

 described for these specific gravities by amounts outside the 

 limits of experimental error in this class of the various expe- 

 riments made. 



A peculiar result was obtained with cells containing sul- 

 phuric acid of sp. gr. 1*2G5, and nearly saturated copper- 

 sulphate solution of sp. gr. 1*175. The E.M.F. was consider- 

 ably depreciated, the average value in four sets of experi- 

 ments with electro-copper and amalgamated pure zinc plates 

 being only 1*084 (maximum 1*095, minimum 1*067). On 

 standing a few hours, copper-sulphate crystals formed at the 

 junction of the two fluids, showing a much less degree of solu- 

 bility of the salt in the acid fluid formed than in pure water. 



Belationsliips between the maarimum E.M.F. developed by a 

 Daniell Cell and the Energy due to the net Chemical action 

 taking place therein. 



113. The above-described results afford a ready explanation 

 of the discrepancies between the valuations of the E.M.F. of 

 a Daniell cell that have been made in absolute measure by 

 various observers, amongst the more important of which may 

 be cited those of Bosscha (Pogg. Ann. ci. p. 517, 1856), 

 von Waltenhofen (Pogg. Ann. exxxiii. p. 478, 1868), 



