342 Dr. Draper ow the Use of a Secondary Wire as a 



troduced, the action of which should correspond with, and 

 abet that of the zinc for oxygen. This takes place when nitric 

 acid or an oxysalt of easy decomposibility is added to the so- 

 lution. The tension of the current is not then determined by 

 the affinity of the zinc for oxygen only, but by all the affinities 

 that can take place, among all the bodies in the exciting cell. 

 We are therefore here led to expand Dr. Faraday's theory, 

 and to regard what follows as directly opposed to the theory 

 of contact. 



Upon these principles, in an ordinary arrangement of cop- 

 per, zinc, and sulphuric acid, the tension of the current is 

 determined; by the sum of the affinities of zinc for oxygen, 

 and hydrogen for copper, diminished by the sum of the affi- 

 nities of copper for oxygen, oxygen for hydrogen, and hydro- 

 gen for zinc. 



But as under all ordinary circumstances the affinities of 

 hydrogen for zinc and copper may be neglected, they being 

 exceedingly small in comparison with the others, we may 

 assume, — 



That the tension of the current is equal to the affinity of 

 oxygen for zinc, diminished by the sum of the affinities of 

 hydrogen and copper respectively for oxygen. 



If now we introduce into the exciting cells nitric acid or 

 sulphate of copper, the affinity of the nascent hydrogen for 

 oxygen is satisfied, and the resistance from this source is 

 nearly exterminated, and the tension of the current is then 

 equal to the difference of the affinities of zinc and copper for 

 oxygen. 



By thus exterminating the resistance arising from the 

 affinity of hydrogen for oxygen, we succeed in raising the 

 tension greatly ; if next we get rid of the affinity of copper for 

 oxygen, the tension ought to become still higher. This may 

 in a measure be effected by making use of a plate of platina, 

 as I found experimentally. 



In all these cases, in which the tension increases without loss 

 of quantity, we directly trace the action to a disturbance in 

 the exciting cells. In ordinary voltaic arrangements, the 

 maximum tension is never reached, because the affinity of zinc 

 for oxygen, which determines the current, is counteracted to a 

 certain extent by the affinity of oxygen for hydrogen. If we 

 satisfy that affinity, an increase of tension is the result, and 

 accordingly as this is more and more nearly effected, more 

 and more of the hydrogen that ought to be evolved disap- 

 pears. This remarkable disappearance of hydrogen has been 

 heretofore noticed, but the true office it served has not been 

 detected. If a battery is charged with nitrosulphuric acid, 



