1888.] upon the Potential of Voltaic Couples. 373 



Table XI.— Ditto at 19° 0. 





Volts. 



Grr£iins. 



Volts. 



drains. 



Volts. 



3 '00 



1*543 



1'65 



1 '4174 







0'3 



1 -2801 



2-85 





1-5 





0-15 



1 2029 



2-7 



1 -5287 



1-35 



» 



0-015 



1 -0156 



2-55 





12 





-0015 



-9084 



2-4 



1 -5258 



1-05 





-00015 



0-7882 



2-25 





0-9 



1 -4317 



-000134 



-7653 



21 



1-5201 



0-75 



1-4117 



-0001206 



0-747 



1-95 





0-6 



1 3932 



water 



5} 



1-8 



1-463 



0'45 



1 3173 







The smallest proportion necessary to disturb the potential lay- 

 between 1 in 3,470,112 and 3,875,000. With the solutions from O'lo 

 to 1*65 grain, the electromotive forces were variable without any 

 apparent cause. 



The proportions of bromine required to change the potential with 

 these couples were as follows : — 



Table XII. 



Mg + Pt with bromine. Between 1 part in 310,000,000 * 



and 344,444,444. 



Zn + Pt „ „ 1 part in 77,500,000 



and 84,545,000 



Cd + Pt „ „ 1 part in 3,470,112 



and 3,875,000 



The magnitudes of the proportions of bromine required to change 

 the potential with the three couples varied directly as the atomic 

 weights of the three positive metals. 



Mg + Pt 4- Chlorine in 465 grains of Water at 13° C. 



Sixteen different solutions, varying in strength from 1*0695 grain 

 to 0*03 grain, with a constant difference of 0*0693 grain, gave each 

 the same potential, viz., 2' 7336 volts. Much gas was set free at the 

 magnesium, but only in the stronger solutions. Owing to the extreme 

 sensitiveness of this couple to chlorine, several series of measure- 

 ments were necessary in order to determine the minimum point with 

 approximate accuracy, and include the entire range of solution. 



