252 Dr. C. E. A. Wright on the Determination of 





Mean tan «. 



Mean tan /3. 



Gramme of H 

 evolved. 



Rise of thermometer. 





3-4170 

 3-9429 

 4-3412 

 4-0508 



1-6234 



1-7780 

 1-8374 

 1-8011 



0-03978 

 004212 

 004372 

 0-04411 



40" 6 scale divisions. 

 37-8 „ „ 

 41'7 „ „ 

 38-8 „ „ 



Average 



3-9380 



1-7600 0-04243 

 Correction for radiation... 



39-725 



4- 0-656 











40-381 



The water- equivalent of the calorimeter was found to be 

 1155 grammes, whilst 23" 38 scale-divisions of the thermometer 

 represented 1°; hence 



h= 1994-9. 



The E.M.F. of affinity to be found, then, is 



3*9380-1*7600 a , 1A 1A8 

 x 6x 1-10 x 10 8 



3*9380 



1994-9 x 1 x 0-000105 x 42 x 10 6 

 0-04243 ; 



or 



1-577 x 10 8 C.G.S. units =1-577 volt. 



The value deduced from Joule's own figures by his mode of 

 experimenting is 34,101 gramme-degrees per gramme-equiva- 

 lent of water decomposed, representing 34101 x%J = 1*504 

 volt ; whilst the value deducible from the best determinations 

 of the heat evolved in the combustion of hydrogen is 34,100, 

 representing 1*504 volt (§ 32). In two other similar sets of 

 observations, Joule obtained the values 34,212gramme-degrees 

 corresponding to 1*509 volt, and 32,356 gramme-degrees cor- 

 responding to 1*427 volt. Unfortunately the data for recal- 

 culating these values, as has just been done with the first set, 

 are not given in his paper ; still the difference between the 

 values of the E.M.F. of affinity, calculated as above and 

 from Joule's heat-values, is apparently no greater than the 

 differences observed in these latter on repetition. It is notice- 

 able that a small error in the value of the E.M.F. of the bat- 

 tery produces a much larger error in that of the calculated 

 result : thus, if in the set of observations recalculated as above 

 the E.M.F. of a Daniell cell be taken as 1*08 instead of 

 1*10 volt, the calculated E.M.F. of affinity comes out 1*511 

 instead of 1*577 volt ; i. e. a diminution of less than 2 per 

 cent, in the value of the Daniell cell makes a diminution of 

 more than 4 per cent, in the E.M.F. of affinity. 



20. In just the same way Joule's experiments on copper 



