Measure of the relative Tension of Electric Currents. 343 



the hydrogen evolved is no longer the equivalent of the zinc 

 expended; in point of fact, the gas evolved is no longer hy- 

 drogen, but a mixture of hydrogen and the binoxide of nitro- 

 gen, as is proved by its burning with a green flame. I took 

 a small pair of plates, the zinc being amalgamated and the 

 platina freshly cleaned, and placed them in a mixture of six 

 ounces of water and one drachm of sulphuric acid, arranging 

 an inverted tube over them, so as to collect the gas from the 

 platina plate. I determined by weighing the zinc plate how 

 much was expended in evolving a given quantity of gas, and 

 then successively adding sulphuric acid until the total amount 

 had reached eight drachms, it appeared that in each instance 

 it required very nearly 1*79 grains of metal. But on adding 

 one drachm of nitric acid to the mixture, the quantity ex- 

 pended rose at once to 2*25 grains, and on adding a second 

 to 3 "00 grains. 



Therefore, unless care is taken that no oxidizing body is 

 present, the voltameter will give deceptive results. This im- 

 portant precept should be perpetually borne in mind by those 

 who employ it in investigations. A few drops of nitric acid will 

 at once vitiate its indications ; and there is reason to suspect 

 that under certain circumstances even the dilute sulphuric 

 acid with which it is charged may undergo partial deoxida- 

 tion, and the evolved hydrogen indicate an amount of electri- 

 city less than is actuall}' passing. 



We are therefore in possession of two distinct methods of 

 indirectly increasing the tension of an electric current. The 

 first depends on the reduction of quantity; the second on 

 satisfying in the exciting cells, affinitiies which tend to anta- 

 gonize that which determines the current. 



Volta's plan of a reduplicated series unquestionably acts 

 upon the first of these principles. It is a fact admitted on all 

 hands, and therefore into the proof it is unnecessary now to go, 

 that the apparent quantity circulating in the whole battery is not 

 greater than that which any one of the pairs could generate. 

 Dr. Faraday has already shown how an enormous quantity of 

 zinc is thus expended, the equivalent of electricity being en- 

 tirely sacrificed, for the sake of increasing the tension. Let 

 us see what are the facts in the case. The first pair of plates 

 developes by the oxidation of a portion of its zinc a certain 

 quantity of electricity, which passing through the electrolytic 

 conductor arrives at the second cell; here however it is stopped, 

 as a transit without decomposition is impossible, a decompo- 

 sition which it is unable to effect. Continually tending to 

 pass, without the passage actually taking place, it remains as 

 it were on the surface of the second zinc plate, in a condensed 



