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p 



358 GALVANISM. 



bodies were, therefore, regarded by Davy as having with relation to each other 

 specific electrical energies. Acids have a negative and alkalies a positive enei- 

 gy, with relation to metals ; while metals have a positive energy with relation 

 to acids, and a negative energy with relation to alkalies. 



Various experiments of a delicate kind were made to establish this general 

 principle. To avoid the disturbing effects which would be introduced by 

 chemical action, the substances of each kind selected for experimental exami- 

 nation were in the solid and dry form. When oxalic, succinic, benzoic, or bo- 

 racic acid, perfectly dry, either in powder or crystals, was touched upon a 

 large surface with a disk of copper, zinc, or tin. insulated, the metal became 

 positive, and the acid negative. Phosphoric acid and zinc gave a like result. 



Metallic plates being brought in like manner in contact with lime, strontia, 

 magnesia, or soda, became negative, the earths being positive. The attraction 

 of potash for water was too strong to allow that alkali to be submitted to trial. 

 Sulphur became positive after contact with a metallic plate, and the supposed 

 exception to this in the case of lead was removed by showing that the sub- 

 stance rubbed against newly polished lead always became positive. 



All these facts went to support the position, that the electrical relation of 

 different substances, as shown by mere contact, was in harmony with the law 

 according to which electricity was developed in the Voltaic apparatus, and with 

 the phenomena of decomposition. To complete the experimental proof of this 

 analogy, it would have been necessary to show that oxygen has a negative and 

 hydrogen a positive electrical energy in relation to the metals. Not being able 

 to accomplish this, recourse was had to the compounds of these substances. 

 Sulphuretted hydrogen in water, used in the Voltaic arrangement of single 

 metallic plates, plays the part of an alkali. To support by a like analogy the 

 negative character of oxygen, he showed that oxymuriatic acid* (chlorine) 

 was more powerfully negative in relation to metal than muriatic acid, even in a 

 higher degree of concentration. 



He assumed as a principle suggested by analogy and supported by experi- 

 ment, that two bodies which have contrary electrical energies in relation to a third 

 body have contrary electrical energies in relation to each other ; that is to say, 

 two bodies, A and B, being successively brought into contact with a third C ; 

 if A is found to be positive after separation and B negative, then it follows that 

 if A and B be brought into mutual contact, A will be positive after separation 

 and B negative. Lime and oxalic acid in a dry and solid state, the former 

 being positive and the latter negative in relation to metals, were brought into 

 contact, and the electricity collected after repeated contacts by a condensing 

 electrometer. The lime was found to be positive and the acid negative. 



Guided by the analogies suggested by such facts, Davy maintained, as a 

 general principle, that oxygen and acid substances have a negative electrical 

 energy in relation to hydrogen and alkaline substances ; and that in the de- 

 compositions and changes presented by the effects of electricity, the different 

 bodies naturally possessed of chemical affinities appear to be incapable of en- 

 tering into combination or of remaining in combination by virtue of these 

 affinities when they are placed in a state of electricity, contrary to the natural 

 relation of their electrical energies. Thus the acids in the positive part of the 

 circuit separate themselves from the alkalies, oxygen from hydrogen, and so on ; 

 and metals on the negative side do not unite with oxygen, and acids do not re- 

 main in union with their oxides ; and in this way the attractive and repellant 

 agencies seem to be communicated from the metallic surfaces (the poles of the 

 ile) throughout the whole of the menstruum. 



* This substance was then supposed to be a compound. 



