48 MR. GASSIOT ON THE RELATION OF ELECTRICAL AND CHEMICAL ACTIONS 
wires was connected at one time with the copper, and at another time with the zinc 
terminal of the battery ; while the wire attached to the other extremity was con- 
nected with the earth. This arrangement being continued for several hours, and the 
paper kept constantly moist, not the slightest evidence of any evolution of iodine 
could be detected, until by a momentary contact made with the further extremity of 
the battery and the ground, either by a wire, or by touching it with the hand, the 
circuit was completed. Here we have a voltaic battery the intensity of which is suf- 
ficient to elicit a spark between its terminals before the circuit is completed, but in 
which antecedent thereto, the slightest chemical action is not appreciable; and this 
when one end is in connection with the earth, and consequently having the intensity 
exalted to a maximum short of actual discharge. 
33. I am aware of the many forms the contact theory has assumed since Volta 
first propounded it ; nor can we lose sight of the many errors which his successors 
have committed in attempting to follow out their favourite views of metallic con- 
tact and electro-motive forces. I am indebted for much information on this point to 
the kindness and industry of Mr. C. V. Walker, who has occupied much time in procu- 
ring me references to the researches of those electricians already alluded to, as also 
to a long list of others w r hose names adorn the pages of science. I could easily have 
added to those I have named, by referring to the experiments of many other authors 
who consider that their favourite theory of contact has been fully established. It is 
not, however, my object to advert to these speculations : we have before us certain 
facts connected with the action of the voltaic battery ; first contact , or successive 
juxtaposition, and simultaneously with it, effects of tension ; then the completion of 
the circuit, and simultaneously with it, development of chemical action and current ; 
but in all these cases contact is first in order, developing tension. Becquerel 
describes it by stating, “When two bodies are in contact the affinities commence 
exercising their action before combination takes place.” M. De la Rive, “The elec- 
tricity of tension developed by contact of heterogeneous bodies.” Faraday, “ That 
the particles of the electrolyte are brought into a polarized state, and raised to a cer- 
tain degree of tension, before discharge takes place but I am not aware that there 
are any experimental facts to prove whether this tension in the voltaic battery, which 
itself is of an opposite character at each terminal, and, as we have seen, can be ex- 
alted so as to produce discharges in the form of sparks for many weeks’ constant du- 
ration (16.), is due to the chemical constituents of the battery, or to mere contact of 
dissimilar bodies, without reference to their chemical affinities. I was therefore most 
anxious to see whether some experiment could not be devised, which would test the 
action in a satisfactory manner, and for this purpose I availed myself of an extended 
series of Grove’s gas battery, described by him in a paper already alluded to (23.)*. 
34. The elements used in this form of the voltaic battery consist of two gases and 
one metal ; with fifty series charged with oxygen and hydrogen, it is stated that the 
* Philosophical Transactions, 1S43. 
