48 Dr Davy's Observatmis on 



fected sensibly the galvanometer, the silver being negative ; while 

 neither of these wires immersed in conjunction with platina wire, 

 produced any sensible effect on the needle. The solution of 

 zinc was formed by means of zinc wire and muriatic acid, the 

 former greatly in excess. After the violent effervescence was over, 

 a very gentle one continued, accompanied by the deposition of 

 oxide of zinc, to which there appeared to be no limit, depend- 

 ing on the decomposition of water. Before the solution was 

 used it was filtered, to rid it of any particles of the oxide or of 

 the metal, which present might have vitiated the result. 



The effect of the contact of other metals applied to this so- 

 lution was hardly less decisive than the preceding, in exhibiting 

 electrical action, through the medium of the galvanometer with- 

 out apparent chemical action. Thus in every instance in which 

 a bright wire of zinc was immersed in it, together with another 

 metal, as platinum, gold, silver, copper, iron, tin, the needle was 

 moved, the effect being greatest with the most negative metal, 

 as platinum, and least with the one approaching nearest to zinc 

 in its electrical relation, as tin ; and, at the same time, not the 

 slightest tarnish could be perceived on the bright polished sur- 

 face of the zinc. 



Even had a chemical effect taken place on the zinc, as the 

 electrical action varied according to the other metals employed .; 

 it may be considered a fact in favour of the theory of contact, 

 and belonging to the same class of phenomena as those lately 

 brought forward by M. A. Bouchardat* ; a class, probably, 

 which will become greatly extended, and will embrace a great 

 variety of effects, which at present appear so mysterious, as the 

 inflammation of hydrogen mixed with oxygen from the contact 

 of porous platinum, the conversion of starch into sugar and 

 mucilage, under the influence of a minute portion of sulphuric 

 acid ; the formation of nitric acid under the influence of car- 

 bonate of lime in rocks and soils, containing potash, on. expo- 

 sure to the atmosphere, and many other chemical changes not 

 less obscure, which hitherto have commonly been considered as 

 instances of predisposing affinity. 

 Malta, 

 \st March, 1834. 



• Annales de Chimie et de Physique, torn. liii. p. 284. 



