Chemical Affinity in terms of Electromotive Force. 



281 



Variation in the E.M.F. due to the use of zinc- 

 and copper-sulphate solutions of different 

 strengths between the limits of sp. gr. 1'0065 

 and 1*175, both solutions being of the same 

 specific gravity in any given case . . . 



Less than 

 ' +-001. 



Maxi- Mini- 

 mum, mum. 



Aye- 



Effect of substituting for fresh electro-copper : — 



Bright rolled copper sheet 



Amalgamated copper (surface wet with "I 

 fluid mercury) J 



Effect of substituting for fresh electro-zinc :— 



Bright cast zinc 



Amalgamated zinc (surface wet with fluid 1 

 mercury) J 



Electromotive force of combinations : — 



Amalgamated zinc — Amalgamated copper . . 



„ „ Electro-copper 



, , , , Bright copper 



Electro-zinc — Amalgamated copper 



,, „ Electro-copper 



„ , , Bright copper 



Bright zinc — Amalgamated copper 



,, „ Electro-copper 



„ ,, Bright copper 



+ •010 

 + •002 



+•005 

 + ■003 



1-115 

 1-116 



1-124 



+•001 

 -■003 



•005 

 •004 



1-110 



1-111 



1-115 



•005 



•010 

 •007 



•005 

 •005 

 •009 



1-116 

 1-118 

 1-124 



1-110 

 1-111 

 1-114 



•006 

 •007 

 •010 



+ •006 

 -■001 



+ ■001 

 -•001 



M13 

 1-114 

 1-120 



1-114 

 1-115 

 1-121 



1-119 

 1-121 

 1-126 



1-109 

 1-110 

 1-112 



•010 

 •011 

 •014 



1-115 

 1-116 

 1-122 



108. The above figures are, as already stated, derived from 

 the observations made during the first four hours after setting- 

 up the cells, the values registered during the first half hour or 

 so with weaker solutions being rejected on account of their fre- 

 quently being lower than the sensibly constant values attained to 

 subsequently. When the cells were allowed to stand for twenty- 

 four hours, or for longer periods, a greater or less fall in the 

 E.M.F. was usually noticed: by taking out any pair of the plates 

 (e. g. the amalgamated zinc and the electro-copper plates) and 

 replacing them by a freshly prepared similar pair, it was found 

 that the value rose again to sensibly the same value as on the 

 previous day when only set up a few hours; so that by taking- 

 out first one and then the other of the pair of plates, determi- 

 nations could be made of the amount of the total fall attribu- 

 table to alterations of either plate separately. The actual 

 values thus obtained fluctuated considerably. As a general 

 rule, it was found that bright copper plates gave the same 

 value after twenty-four hours' immersion as they did at first ; 

 but occasionally the value was lowered by '002 to *004. 

 Electro-copper plates usually gave values less by -002 or *003 



