Researches into the Cause of Voltaic Electricity, 275 



ber of facts in 1828, has since that period been the subject of 

 a warm controversy. It has been attacked by many physicists 

 upon two grounds: 1. That electricity is produced by the 

 simple contact of bodies ; 2. That a good theory of the pile 

 cannot be given without admitting Volta's electromotive force. 

 A reply to the second objection is unsuited to a portion of the 

 memoir devoted to the chemical theory of the pile ; I shall here 

 therefore notice only the first, and endeavour to show the ex- 

 actitude of the principle which I have stated above. 



The reason that it has been, and is still often supposed 

 that the simple contact of two heterogeneous bodies develops 

 electricity, is the difficulty of securing them from all calo- 

 rific and mechanical, and especially from all chemical ac- 

 tion. Are the bodies placed in a liquid ? When the liquid 

 does not attack them the air dissolved in the liquid oxidates 

 them if they are metals, or the water of the solution forms 

 hydrates with them if they are oxides. Are they left in 

 the air, or placed in some other gas? It is soon evident 

 from the alteration of their surfaces that they are attacked 

 by the air or the gas ; the finger or the humid substance 

 with which they are touched is also often the cause of che- 

 mical alteration at the points of contact. Indeed nothing 

 is more difficult than to secure the absence of chemical action 

 in these experiments. And when we consider on the one hand 

 how feeble is the electricity produced, since to perceive it the 

 assistance of the most delicate apparatus is required ; and on 

 the other what an immense quantity of electricity may be de- 

 veloped by the most feeble chemical action, as has been proved 

 by the experiments of Mr. Faraday ; we ought no longer to be 

 surprised that excessively feeble chemical action, the traces of 

 which cannot be detected but at the end of a certain time, may 

 give sensible signs of electricity. 



But it is not impossible to exclude all chemical action, and 

 then no disengagement of electricity is perceptible even with the 

 most delicate apparatus. Thus pairs of platina and gold, or of 

 platina and rhodium, in extremely pure nitric acid, do not give 

 any current to the most sensible galvanometers; the same thing 

 occurs with platina and palladium in diluted sulphuric acid. In 

 order to the success of these experiments it is necessary to em- 

 ploy only highly purified substances, for one drop oi hydro- 

 chloric acid in the nitric, or of nitric acid in the sulphuric, 

 immediately renders the pairs active. From experiments 

 of this kind I shall produce one which appears to be pos- 

 sessed of some interest. Two plates of perfectly polished 

 steel were immersed in a flask filled with a solution of potash ; 

 one was insulated, and the other metallically fixed by itsextre^ 



2 N 2 



