424 Prof. R. Bunsen's Spectral- Analytical Researches. 



21*3 and 18'5. In order to arrive at a more exact number, the 

 current-intensity of the battery J was determined ; and after in- 

 tercalation of a conduction-resistance I (expressed in British- 

 Association measurement) , this number J was again determined. 

 The electromotive force e and the conduction-resistance of the 

 cell co are therefore expressed in absolute measurement as fol- 

 lows : — 



JZ T 



e= 





(2) 

 (3) 



The observations were carried out in the following manner. 

 The intensity of the current after it had become stationary was 

 first of all determined from the mean value of five needle-obser- 

 vations made at equal time-intervals; these observations were 

 repeated after the intercalation of the resistance I; and the two 

 series, without and with the resistance, were then a second time 

 repeated. The four mean angle-readings, i v z 2 , i 3 , i 4 , were thus 

 obtained. By the help of formula (1) the value of J was calcu- 

 lated from 2 2 , that of J l from the mean of i x and i 3 ; a value for 

 J and J 2 was again deduced from i 3 on one hand, and from i 2 

 and i 4 on the other. 



The electromotive force e and the conduction-resistance co of 

 the ordinarily employed batteries, and also of the chromic-acid 

 battery, are given in the following Table, along with the obser- 

 vations upon which these values are based : — ■ 



l 



Ji 



J 



e 



Mean value 

 of e 



Silver-chlo- 

 ride battery. 



1-258 

 19-40 

 4-55 



7-47 



1-258 

 18-83 

 4-22 

 6-85J 



7-16 



0-385 | 0-364 



Daniell's 

 battery. 



1-258 

 1164 



4-90 

 10-65 



1-258 

 11-79 



4-94 

 10-69 



10-67 

 0-915 | 0-907 



Grove's 

 battery. 



0-5126 

 33-33 

 1733 

 18-51 



0-745 

 29-64 

 13-47 



18-40 



18-45 

 0-555 I 621 



Zinc-carbon 

 battery. 



Chromic-acid 

 battery. 



1-258 

 66-55 

 1209 

 18-59 



1-258 

 66-22 

 12-07 



18-57 



18-58 

 0-279 | 0-280 



1-258 

 5101 

 12-45 

 20-72 



1-258 

 51-00 

 12-65 

 2116 



20-94 

 4061 0-415 



From these experiments it is evident that the chromic-acid bat- 

 tery without clay cells possesses an electromotive force greater, by 

 about 13 per cent., than that of Grove's or the carbon-zinc bat- 

 tery. On observing the valve of e from time to time, a period is 

 noticed during which this value increases while the battery is 

 steadily undergoing exhaustion. By causing an unexhausted 

 chromic battery to act against a partially exhausted battery, it 

 becomes evident that the increase in the electromotive force is, 



