216 Mr. J. Frideaux on the Theory of Voltaic Action. 



current when two plates of zinc act in the same acid, is, one 

 being tarnished and therefore "negative"* to the other; an 

 explanation inconsistent with an experiment of Mr. Sturgeon's 

 (41), derived probably from this very paper of Davy's. 



Sect. III. Of the initial Electromotion in the Metals. 



12. Volta, finding that he could not exalt his electromotive 

 power by piling pairs of zinc and copper one upon another, 

 thought of interposing flakes of wet paper between the pairs, 

 and succeeded. Other investigators have since varied the 

 form of the apparatus, and every one of its elements; — have 

 still found zinc and copper the most convenient metals for the 

 purpose, but have made great improvement in the liquid. 

 Nitric acid, properly diluted, seems, under all circumstances, 

 the most efficacious of these ; but for the electromotive in- 

 fluence only, the most effective arrangement is zinc, alkali, 

 acid, copper. 



13. With whom or when this discovery originated, I do 

 not know; but it is stated in Berzelius, Traite de Chimie 9 

 i. 152, that the little apparatus described (9) filled, half with 

 alkaline, half with acid solutions, the zinc plunged in the al- 

 kali, the copper in the acid ; produces more decided effects 

 than when the zinc is placed in the acid, the copper in the 

 alkali. In repeating this experiment I was annoyed with the 

 negative effect of the copper stem, passing up from the zinc 

 through the acid, from which more hydrogen was often given 

 off than from the little copper plate which came over from the 

 adjoining glass. This rendered the results variable; and to 

 obviate it the plates were bent off at right angles, so as to lie 

 flat, and shallow cups were employed instead of glasses ; the 

 depth of the strata of alkali and acid being thus reduced to 

 ^ or § inch each, the stems had less interfering effect. The 

 steadiness of result thus produced, suggested a simpler form 

 of the experiment. 



14. A glass tumbler being filled to the depth of J inch 

 with solution of common salt alkalised .with potassf ; an inch 

 deep of diluted muriatic acid J was poured on carefully, so as 

 to float above the alkali, without disturbing it. The latter 

 having been coloured with logwood, the surface of separation 

 was as distinctly visible as that of the glass was from the 

 table. 



A plate of zinc, and another of copper, each 2 inches 



* The term " negative" here, and in other parts of the first section of 

 Davy's paper, seems to be misapplied. 



+ Salt \ ounce, water \ pint, liq. potassa: 1 ounce. 

 \ Water 1 pint, muriatic acid 3 drachms. 



