for Electrometric Measurements. 177 



The decrease in electromotive force of each of the two ele- 

 ments for low temperatures between 0° and 20° amounted to 

 only 0*015 per cent, for an increase in temperature of 1°. 

 But the temperature-coefficient increases with increase of 

 temperature. With element II. it amounted to 0'053 between 

 20° and 30°; with element III. to 0'045 between 21° and 32°, 

 and between 32° and 55° even to 0-061. For Latimer-Clark's 

 element, Helmholtz and von Kittler* agree in finding it to be 

 0*08. Within the narrow limits within which electrometric 

 measurements are commonly made, the influence of tempera- 

 ture upon the electromotive force of the dry Daniell element 

 may be altogether neglected. 



The effect of short-circuiting is seen from the following 

 experiments made with elements I., II., III. 



The element was short-circuited for a certain length of 

 time, then contact was broken, and the difference of potential 

 measured. We do not thus obtain actually the lowest value 

 which the difference of potential may attain, since this in- 

 creases even during the few seconds which the measurement 

 requires ; but we do obtain the value with which we are 

 actually concerned in our measurements. 



The elements I. and II. were scarcely influenced at all by 

 having the circuit closed for half a minute ; but element II. 

 sank from 1*000 to 0*997, but quickly recovered itself com- 

 pletely. The following changes were caused by more pro- 

 longed closing of the circuit : — 



I. II. 





0*998 





1-000 



After 10 minutes 



... 0*991 



After 1 hour ... 



... 0*994 



)) ^ 53 



... 0*988 



„ 15 hours ... 



... 0-988 



„ 14 \ hours .. 



.... 0*975 



„ 20 „ ... 



... 0-988 





.... 0*996 





... 0*993 



„ 15 „ 



.... 0*986 



151 



... 0*987 



5 minutes open .. 



.... 0-994 



„ 24 „ ... 



... 0-986 







„ OJ „ 



... 0-987 







5 minutes open... 



... 0*994 



III. 



1-000 



After 15 minutes 0*996 



„ 50 „ 0*994 



„ 17 hours 0*989 



5 minutes open 0*992 



After the lapse of a quarter of an hour the open element had 

 in all cases recovered its former electromotive force. 



* Kittler, Sitzimgsb. loc. cit. p. 501. 

 PJdl Mag. S. 5. Yol. 18. No. 112. Sept. 1884. N 



