THE QUARTERLY JOURNAL OF THE CHEMICAL SOCIETY OF LONDON. February 19 1849. The President in the Chair. M. Claudet presented a portrait of Dr. M. Faraday taken from a Daguerreotype. Messrs. Edward J. Chapman arid John E. Mayer were elected Members of the Society. The following papers were read IX.-An account of Some experiments with Voltaic Couples. By MR. RICHARDADIE,Liverpool. INcontinuing the experiments submitted last year for the con-sideration of the Chemical Society in which I sought to show that a metallic oxide acted as a negative element to bright portions of the metal from which such oxide was derived I formed a voltaic couple with two similar pieces of zinc one of which was amalgamated while the other possessed a clean-scraped metallic surface.When this couple was connected in the usual manuer with a delicate galvanometer and immersed in oxygenated water I found it easy to obtain the voltaic current at pleasure either from the amalgamated surface as the positive or from the scraped surface as the positive element. The plates were immersed in the water and allowed to remain for some time till the galvanometer in connection with them fell to near zero. The amalgamated plate was then taken out and the surface wiped clean ; on re-immersion the galvanometer immediately indicated that VOL 11.-NO. VI H MR. ADIE ON VOLTAIC COUPLES. the bright amalgamated surface was positive to the other which had remained for some time in the water and was slightly oxidized.Again allowing a space of time for the galvanometer to return near to zero the zinc plate with a scraped surface was removed and again cleaned; when put into the water the galvanometer showed that its surface was positive while the amalgamated surface had now become negative the reverse of what it was in the first trial. These experi- ments were repeated with uniform results the sole condition which regulated the direction of the voltaic current being the state of the surfaces of the pieces of zinc with reference to oxidation Unlcss care was taken however to keep the amalgamated surface untouched I generally found it acting as the positive plate a result to be expected from the circumstance of the amalgamation of the metal rendering the oxide formed on its surface far more easily removeable than the oxide formed on the surface of unamalgamated zinc.From these experiments the object of amalgamating zinc surfaces in voltaic batteries would appear to be to prevent the formation of oxide of zinc on the positive side where it would act as a negative element and waste a portion of the power of the battery in gene- rating local currents. In oxygenated-water batteries the metallic oxides are removed from thc surfaces of the plates by mechanical means only there being no acid present to remove them in the form of soluble salts; but in batteries where acids are used the oxides are removed by combining with part of the acid to form soluble salts. In this case I presume that amalgamating has still the same kind of action which we find exerted in the oxygenated-water battery namely that the particles of the oxidc to be combined with the acid are more feebly attached to the amalgamated metallic surface than to the same surface unamalgamated and are consequently more readily dissolved.The usual explanation given of the advantage resulting from amal- gamated zinc is I believe that it prevents impurities in the zinc from forming local actions but I apprehend that with the purest zinc a coating of oxide on its surface will in an oxygenated-water battery have greater influence in destroying its positive action than any of the metals found associated with common zinc as impurities. In continuing the experiments in which pure specimens of metals were enclosed with distilled water in hermetically sealed glass tubes and where I had found that iron possessed the power at ordinary temperatures of slo~vly decomposing water generating hydrogen I prepared by voltaic action specimens of antimony bismuth lead and tin and placed portions of each of these in test-tubes with pure MR.ADIE OW VOLTAIC COUPLES. water ;the tubes were afterwards hermetically segd the greatest pains having been taken to expel absorbed air from the water by ebullition. In none of these tubes could I discover the slightest evidence of the decomposition of the water. The tubes were then removed to a sand-bath where they were maintained for two months at a temperature of loooFahrenheit above the ordinary temperatures of the weather without any of them showing an increase of internal pressure through the generation of hydrogen.The first three of these metals are held by chemists to be in- capable of decomposing water at any temperature hence it was not to be expected that like iron they should possess a slow power of' decom-posing water ;but having found that when they were formed into the positive elements of voltaic couples excited by water in a rapid state of ebullition the attached galvanometer always indicated a decided action I felt desirous to try carefully whether the effect could be due to a decomposition of the water. As no evidence of this kind could be obtained from theseexperiments it appeared to me that the action of such voltaic arrangements must be explained on the prin- ciple that water boiling in the atmosphere always contains some portion of absorbed air and that it is the oxygen of this air which excites the couple.A plate of copper associated with one of platinum and attached to a delicate galvanometer gave a perceptible action when excited by boiling water when the plates were at the surface the action was greatest; but when these were placed beneath the surface of the water there was still decided action. At a depth of 8 inches below the surface a voltaic current was generated which according to the above view of the action of such a couple could only arise from a portion of atmospheric air reaching the plate.