Electromotive Force of different Forms of the Clark Cell. 149 



Per cent, of sol. (p) . . 



0° 

 29-50 



10° 

 32-24 



20° 

 35-13 



30° 

 38 *22 



40° 

 41 -33 



50° 

 43-45 



ZnS0 4 in 100 aq 



41-85 



47-58 



54-16 



61-86 



70-44 



76-84 



Compare Poggiale* . . . 



43-02 

 -1-17 



48 -36 

 -0-78 



53 -13 

 + 1-03 



58 -40 

 + 3-46 



63-52 

 + 6-92 



68 -75 

 + 8-09 



§ 24. Change of E.M.F. at Higher Temperatures. (Betiveen 30° and 



50° C.) 



Finding that there was a change in the continuity of the curve 

 representing the temperature variation of the E.M.F. at temperatures 

 above 41° C, we decided to investigate this point more closely, although 

 the temperatures in question lie beyond the range of the practical use 

 of Clark cells. By a slight modification of the heating arrangements, 

 the constant temperature baths were enabled to reach steady tempe- 

 ratures up to and beyond 50° C. The following series of observations 

 were taken with several cells of different types, in a manner similar 

 to that which has been already described. Each line represents the 

 mean of tbe different cells at each point. The observations given in 

 different lines were taken on different days, in the order in which 

 they are given in the table. An interval of several months inter- 

 vened between the first and tbe last half of the table. 



Table VI.— Change of E.M.F. between 30° and 50° C. 





Difference in millivolts from 





Temperature 



15° C. 



Difference from 

 linear formula 



centigrade. 







(L). 





Observed. 



Formula (L). 



40 -60° 



35-81 



30-72 



5-09 



30 -14 



19 -78 



18-17 



1-61 



30-32 



20-00 



18-38 



1 -62 



35-44 



27 *39 



24-53 



2-86 



42-58 



36-56 



33-10 



3-46 



46-74 



41 -14 



38 -09 



3-05 



48 -58 



43-50 



40 -30 



3-20 



35-79 



28-08 



24-95 



3-13 



40 09 



34-99 



30-11 



4-88 



42-79 



36 76 



33-35 



3*41 



44-70 



38 -88 



35-64 



3-24 



41 -54 



35-45 



31 -85 



3-60 



* ' Watt's Dictionary of Chemistry.' Muir and Morley, vol. 4, p. 581. 



M 2 



