330 Royal 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 difierent 
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 every 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 successfullj^ 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 was 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-plate 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 autlior shows, that the interposition in the circuit of the smallest 
f j uantity of an electrolyte, which acts chemically on either of the metals, 
the arrangement remaining in all other respects the same, is imme- 
