21 



tween the fire and chimney by shutting the flue, we check the 

 combustion ; and such is the nature of the battery. 



In order to increase the intensity of the battery Mr. Smee has 

 introduced platinized silver, which possesses the singular pro- 

 perties of evolving, or rather liberating the hydrogen with great 

 facility ; hence the draft is thus increased, and consequently the 

 combustion of the zinc accelerated. 



Whatever may be the real origin of the current, it is very 

 evident that its direction is from the positive to the negative 

 plate, and that it is the positive plate alone which produces the 

 action and causes the decomposition. 



It is not necessary to enlarge on this subject here, as the 

 reader may refer to Smee^s admirable treatise on this interesting 

 part of our inquiry. We shall only remark, that the metals in 

 solution are reduced into their metallic state in the decomposing 

 trough of the battery on the negative plate, i. e. the plate which 

 evolves the hydrogen, and apparently contrary to the direction 

 of the current. 



But when we examine more minutely into the immediate 

 cause of the reduction of the metal on the negative plate, we find 

 that it is not produced directly by the current, but is the result 

 of a secondary action ; thus a solution of copper being subjected 

 to a voltaic current, the hydrogen in oozing out of the negative 

 plate seizes upon the oxygen of the oxide of copper, and forms 

 water, whilst the metallic copper is thrown down on the plate ; 

 and as long as the strength of the metallic solution is kept up 

 and remains in contact with the plate, the hydrogen issuing out 

 will continue to liberate the metal from the oxygen, and the re- 

 duced mineral will present the appearance of a lateral growth 

 from the plate. 



Whilst the above action is going on, on the negative plate, a 

 contrary effect is taking place on the positive. If the positive 

 plate of the decomposing trough be copper, as is always the case 

 in reducing copper solutions, the acidulated water in contact 

 becomes decomposed by the oxygen uniting to the copper, the 

 quantity of copper reduced at this plate being about equal to 

 that forming on the opposite plate, and thus the strength of the 

 solution is kept up. 



Hence we observe that there is no real contrary current to 



