H. S. Carhart — One-Yolt Standard Cell. 



65 



E. M. F. values. Perhaps no closer numerical agreement 

 could be expected in the case of a variable E. M. F. 



In the light of the above conclusions and with thermo-elec- 

 tric data furnished by Bouty and by Chroustchoff and Sitnikoff* 

 it is easy to draw the conclusion that the temperature coeffi- 

 cient of the calomel cell should be negative and of small value. 



The thermo-E. M. F. or value of — for Zn - ZnCl.-Zn is 



given by Bouty as 0-000696 ; Chroustchoff and Sitnikoff found 

 that of H£-Hg a Cl 2 -ZnCl 2 -Hg 2 Cl 2 -Hg to be 0-00066 be- 

 tween 0° and 50° C. 



Hence the coefficient should be, 



0-00066 — 0-000696 



dE 



dT 



0-000036. 



The value of ^= for zinc in zinc salts given by Chroustchoff 



and Sitnikoff would give a larger negative coefficient than the 

 above. 



I have therefore investigated this subject to ascertain if this 

 case furnishes an exception to the law of temperature coeffi- 



10° 15° 2C° 25° 3(T 35° W° 45" <J(T 



cients already announced. The result confirms the law and 

 shows Bouty's result to be in error The determinations were 

 made by means of the experimental cell in the manner already 

 indicated. Tables II and III contain the observations which 

 are expressed graphically in the two curves of fig. 2, in which 



A. relates to Zn— ZnCl 2 — Zn, Table II, and 



B. to Hg-Hg 2 Cl -ZnCl 2 -Hg 2 Cl 2 -Hg, Table III. 



*Comptes Rendus, vol. cviii, 1889, p. 937. 



\m. Jour. Sci.— Third Series, Vol. XLVI, No. 271.— July, 1893. 

 5 



