330 Koyal Society : — Dr. Faraday's Researches in Electricity. 



Volta, proceeds to give an account of various modifications in the 

 theory introduced by subsequent philosophers ; and also of different 

 variations in the views of those who, in the main, have adopted the 

 chemical theory. Being desirous of collecting further and more 

 decisive evidences on this important subject, he engaged in the series 

 of experimental researches which are detailed in the present 

 memoir. 



It is assumed, he observes, by the advocates of the contact theory, 

 that although the metals exert powerful electromotive forces at their 

 points of mutual contact, yet in eveiy complete metallic circuit, 

 whatever be the order or arrangement of the metals which compose 

 it, these forces are so exactly balanced as to prevent the existence 

 of any current ; but that, on the other hand, fluid conductors, or 

 electrolytes, either exert no electromotive force at their place of 

 contact with the metals, or, if they do exert such a power, the forces 

 called into play in the complete circuit are not subject to the same 

 law of compensation as obtains with circuits wholly composed of 

 metallic bodies. The author successfully combats this doctrine, by 

 bringing forward a great number of instances, where certain fluids, 

 which have no chemical action on the metals with which they were 

 associated in the circuit, are in themselves such good conductors of 

 electricity, as to render evident any current which could have 

 arisen from the contact of the metals, either with each other or with 

 the fluid ; the evidence of their possessing this conducting power 

 being their capability of transmitting a feeble thermo-electric cur- 

 rent from a pair of plates of antimony and bismuth. The following 

 he found to be fluids possessing this property in a high degree ; 

 namely, a solution of sulphuret of potassium, yellow anhydrous ni- 

 trous acid mixed with nearly an equal volume of water, very strong 

 red nitric acid, and a mixture of one volume of strong acid with two 

 volumes of water. By employing the solution of sulphuret of po- 

 tassium as an electrolyte of good conducting power, but chemically 

 inactive with reference to either iron or potassium ; and associating 

 it with these metals in a circuit, formed by two test-glasses con- 

 taining the solution, into one of which v/as immersed a plate of pla- 

 tina and a plate of iron, and in the other two plates of platina ; and 

 the circuit being completed by wires of the same metals respectively, 

 joining the iron-j^late in the first glass with one of the platina-plates 

 in the second, while the other two platina-plates were united by 

 platina wires, interrupted at one part by a short iron wire which 

 joined their ends ; — it was found by the test of an interposed galva- 

 nometer, that, as no chemical action took place, so no electric cur- 

 rent was produced ; yet the apparatus thus arranged could transmit 

 a very feeble thermo-electric current, excited by slightly raising the 

 temperature of the wires at either of their points of contact. Hence, 

 the inference may be drawn, that the contact of iron and platinum 

 is of itself productive of no electromotive force. On the other hand, 

 the author shows, that the interposition in the circuit of the smallest 

 quantity of an electrolyte, which acts chemically on either of the metals, 

 the arrangement remaining in all other respects the same, is imme- 



