62 



H, S. Carhart — One- Volt Standard Cell. 







Table I. 







No. 



30. Clark. 





No. 8. 



ZnCl 2 • 



Resistance 





Resistance 





Electromotive 



to balance. 



Temp. C. 



to balance. 



Temp. C. 



force in volts. 



9401 



18°-25 



6572 



13°-7 



1-0000 







6608 



48-9 



1-0055 







6604 



48*0 



1-0049 







6598 



45-4 



1-0040 







6592 



40-7 



1-0031 







6589 



36-4 



1-0025 



9402 + 



]8°*25 



6586 



30-2 



1-0020 







6583 



26-7 



1-0016 







6581 



23-7 



1-0013 







6579 



20-4 



1-0010 







6577 



17-2 



1-0007 







6576 



15-0 



1-0005 



9403 



18°'l 



6573-5 



10-0 



1-0001 



The E. M. F. of the Clark is taken as 1-434 at 15° ; tempera- 

 ture coefficient — -00077. It will be observed that the cell does 

 not recover its normal E. M. F. immediately on descending 

 temperatures. This hysteresis phenomenon however is small, 

 amounting only to an error equivalent to about three degrees 

 of temperature. The entire change of temperature of about 

 40° took place within three hours. The observations of the 

 table are plotted in the curve of fig. 1. The curve is approxi- 

 mately a straight line between ten and forty degrees. Beyond 



this point the coefficient increases rapidly. The equation of 

 the curve contains not only a quadratic term but one which 

 is a function of a still higher power of the temperature. The 

 following equation fits the observations fairly well : 



E t = 1 + -000085P- 15) + -0000006^- 15) a + -OOOOOOOlp- 15) 3 . 



Between ten and thirty degrees the relation between E. M. 

 F. and temperature may be expressed as follows : 

 E t = l + *000094(£ — 15). 



