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



21. These numbers 1*198 and 2*395 volts lie close to those 

 calculated from Joule's figures by his own method of experi- 

 menting, and also to those calculated from the heat evolved in 

 the synthesis of copper and zinc sulphates from the metal, 

 oxygen, and dilute sulphuric acid ; these latter quantities were 

 found by Thomsen (Deut. diem. Ges. Berichte, 1872, vol. v. 

 p. 170) to be respectively 56,216 and 108,460 per " gramme- 

 molecule," or 28,108 and 54,230 per gramme-equivalent. A 

 somewhat smaller number than the former of these (viz. 26,568) 

 was found by Favre for the "heat of formation" of copper 

 sulphate from copper, oxygen, and dilute sulphuric acid by the 

 method referred to in § 5. These various results may be thus 

 contrasted : — 



Copper Sulphate. 



Observers furnish- 

 ing the principal 

 data for calcu- 

 lation. 



Nature of method 

 of calculation. 



Heat evolved. 



E.M.F. of 



affinity in 



volts (1 volt 



= 10*0.8.8. 



units). 



Per 



gramme 



of metal 



deposited. 



Per grm.- 



equivalent 



of metal 



deposited. 



Joule j 



Joule's own method, 

 described in §§ 2 & 3. 



>> 



>» 



From formula 

 C=B-H X J(§11). 



From formula 

 «=H' X J(§§10&11). 



1 8364 



856 

 796-5 



26556 



27178 

 25289 



1-171 



1-199 

 1-115 



" 



Joule 1 



Julius Thomsen j 

 Favre 



829-6 



26341 



1-162 



} 



} ■■■■■• 



28108 

 26568 



1-198 



1-240 

 1-172 





' Zinc Sulphate. 



Joule \ 



Joule's own method 

 (§§ 2 & 3). 



tf 



From formula 

 « = E-H X J(§11). 



From formula 

 « = H' X J(§§10&11). 



1 15231 



1547 

 1619 



49501 



50277 

 52617 



2-183 



2-217 

 2320 





Joule \ 



Julius Thomsen I 



15630 



50798 



2-240 





54230 



2-395 

 2-392 



22. In reference to Julius Thomsen's values, it is noticeable 

 that some slight uncertainty in the precise values of the heat- 

 developments in the syntheses Cu, O, S0 3 aq.,and Zn,0, S0 3 aq. 



