278 M. De la Rive's Researches 



two plates be immersed in a solution of sulphuric acid, the 

 oxygen always appears upon the positive plate a few seconds 

 before the hydrogen is seen upon the negative ; a fact which 

 can only be explained by admitting that the first quantities of 

 hydrogen disengaged have been employed in deoxidating the 

 negative metal : it is not necessary that this metal be very 

 oxidable ; either silver or copper will answer ; all that is ne- 

 cessary is that the pile be feeble, and the solution a good con- 

 ductor. 



The experiment which is considered as the most favourable 

 to the theory of contact is that of putting in contact platina 

 and peroxide of manganese, when the former of those sub- 

 stances is found to be positive and the latter negative. Other 

 peroxides, such as that of lead, will give the same results. By 

 putting a thin plate of wood, instead of one of platina, upon 

 the plate of the condenser, and by placing on the wood the 

 peroxide which is held between the ringers, the condenser of 

 positive electricity is charged. If a piece of paper steeped in 

 pure water, or what is still better, in acidulated water, be sub- 

 stituted for the wooden plate, and the peroxide be touched 

 with a piece of wood or with a dry finger, the condenser of 

 negative electricity is charged. Thus the development of 

 electricity is not due to the contact, but to the slight deoxi- 

 dation that the peroxides, such as those of manganese and 

 lead, undergo by contact with humid bodies, or to the foun- 

 dation of hydrates due to the same circumstance. In the 

 same manner may be explained the slight instantaneous 

 current which M. Becquerel obtained by immersing peroxide 

 of manganese and platina in pure water. This current only 

 occurs when the circuit has been interrupted for fifteen or 

 thirty minutes, in order to allow of the accumulation of elec- 

 tricity due to the slight chemical action; which accumulation, 

 as we shall presently see, happens in this instance alone, in 

 consequence of the imperfect conductibility of the elements 

 of the pair. The same phenomenon occurs with gold and 

 platina, and arises from the slight oxidation of the gold ef- 

 fected by the operation of the air dissolved in the water. It 

 is true it is very feeble, but if allowed to accumulate for about 

 half an hour it will be capable of producing an instantaneous 

 current perceptible with a very sensible galvanometer. 



Principle II. — All chemical action disengages electricity ; 

 but the electricity disengaged is not, in eveiy case, nor under 

 every form yrro-portional to the vivacity of the chemical action. 

 Two principal circumstances may explain this anomaly ; viz. 

 the immediate recomposition in a larger or smaller proportion 

 of the two electricities at the points at which they are separated 



