[ 485 ] 



LXXIV. On Galvanic Circuits composed of two Fluids, and of 

 two Metals not in contact. By Professor J. C. Poggen- 



DORFF.* 



IN support of the so-called Chemical Theory of galvanism^ or 

 rather of that view which places the source of voltaic electricity 

 solely in the chemical afSnity of the positive metal of the circuit, 

 \dz. the zmc, for the electro-negative constituent of the fluid, Mr. 

 Faraday has of late brought forward in an especial manner the 

 three following arguments : — 



1. The production of a spai'k on completing the junction of a 

 simple chcuit. 



2. The electrolytic law. 



3. The preponderance of a circuit of zinc, platina, and sul- 

 phuric acid, over one formed of the same metals and a so- 

 lution of the iodide of potassium. 



With respect to the first point, the production of a spark 

 on making the connexion between a single pair of plates, 

 Faraday, in the Eighth Series of his Experimental Researches, 

 lays much stress upon it, and for this reason ; — because it must 

 have passed before the metals could have come into contact, 

 and thus not only proves its origin from pure chemical forces, 

 but also the superfluousness of metallic contact for exciting 

 voltaic electricity t; in the further progress of his labours the 

 Enghsh philosopher seems, however, to have some doubt as to 

 the reality of a spark on junction ; at least he expresses himself 

 in his ninth series in a manner which induces the belief that he 

 considers this spark to be a heating and ignition of the mer- 

 cury employed in the experiment at or after the moment of 

 junction^. 



Moreover, Professor Jacobi, in an experiment performed for 

 the very purpose of solving this doubt, in which the wire of junc- 

 tion of a simple, very powerful zinc-platina circuit was interrupt- 

 ed by a layer of air only 0*00005 inch, was not able to perceive 

 the least sign of the passing of a spark at the place of dis- 

 junction §. And recently Professor Draper, in New York, could 

 not even observe the spark in a perfect vacuum before direct 

 contact between the mercury and the wire which formed the arc 

 of junction of a simple circuit 1|. 



* From Poggendorff 's Annalcii, vol. xlix, January, 1840 : translated by 

 Mr. W. Francis. 



t Experimental Researches, Ser. viii. §. 915, 



+ Ibid §. 1074. 



§ London i^^({ Edinburgh Philosophical Magazine, vol. xiii. p. 401. 



II Ihid. vol. XV. p. 34Q. 



