9ji jVJlr.Iv B. Cooke on l/te Measurement of C/temical Affiniij/i 

 a)ftCC,.>j^LicU cau Imj Cjasily weasuird and allowed for. In fact, 



■\,.> >-.l.ul,ui >i: ,..:. ^J[ = 5X:(46 + ^-)>-. 



Whietei^'ife'thfe wsistancc rtf the ^galvanometer coil. The wife 

 was pushed down the tube until an elevation was attained^ 

 at which the momentary deflection of the needle by a zinc and 

 copper circuit was 10^, which was found to require a resi^tahiijife 

 oi'twenty-one divisions of the tube, or 



^l' ( ■/■' ' I = 10 X (21 + ?•) = 5 X (IG + r), 



Gdiisequently^ in ttll?*ttie^8tu'efttients Of intensity, ion^ S^s befeii 

 added to the number of the divisions of the tube, to allow for the 

 I'esistance of the coil. 



^Measured thus, the intensity of the current from zinc and 

 copper plates in water, or the affinity of zinc for oxygen, less the 

 affinity of copper for oxygen, 



while the intensity produced by zinc and platinum plates 'itt th6 

 same fluid 



= 5(49 + 4) =265; 



leaving, if the platinum be really inert, only 15 for the affinity 

 of copper for oxygen, or only y^yth pail'jp^; tji^t of xiue fpi* 



oxygen.^ ^ . . ^ ' '■■ ^^'i-:-: '' ■ : '' ':i^'-. 



Considering the easy oxidation of copper and its fierce decom- 

 position of nitric acid, this small estimate of its force of affinity 

 for oxygen does not seem a })robable result, and the platinum 

 may be fairly suspected of exercising some counteracting influ- 

 c^CQ. When oxygen is nascent upon the surface of platinum, 

 even though it be urged in addition to its own affinity by the 

 current affinity of a thousand cells, no combination is effected. 

 Can it be that there is a tendency to combine which is sensible 

 to the galvanometer, but by some hidden influence which is not 

 sensible to the galvanometer the combination is prevented? 

 The supposition is inadmissible until no other explanation can 

 be found. 



The attempt was made to ascertain the limit, if there be one, 

 tb which the polarization of platinum can be carried, and whether 

 both anode and cathode are equally aiiected. Two platinum 

 plates aijd one of copper were arranged in a glass of rain-water 

 without contact with each other. The copper plate was connected 

 with the galvanometer. The ])air of platinum plates were joined 

 ifi .series with a battery bv which the water between them was 



