GALVANISM. 347 



were enlarged by the apparatus of the laboratory of the Royal Institution, 

 which was now under his direction. The Voltaic apparatus consisted of 

 > a scries of 150 pairs of four-inch plates of zinc and copper, and a series 

 of 50 pairs of zinc and silver of the same magnitude. The plates were 

 cemented into four troughs of wood, according to the method proposed by 

 Cruickshank. Another apparatus was provided, consisting of a series of 

 twenty pairs of thirteen-inch plates of zinc and copper. 



With the batteries of the smaller plates he repeated some of the experiments 

 on the production of the spark, and the combustion of the metals which had 

 already been made. When the poles consisted of two knobs of brass, the 

 spark which attended the discharge was of dazzling brightness, and one eighth 

 of an inch in apparent diameter. Between pieces of charcoal it had a vivid 

 whiteness, and the charcoal remained red-hot for some time after the contact 

 was broken, and threw off bright coruscations. The current passing through 

 steel wire jyo tn of an inch in diameter, rendered it white-hot, and caused it 

 to burn with great splendor. Gold, silver, copper, tin, lead, and zinc, were 

 also burnt. Platinum in thin slips was rendered white-hot and fused. 



Fourcroy, Vauquefin, and Thenard, had investigated the different effects pro- 

 duced by enlarging the plates of a battery, and by increasing their number. 

 They demonstrated that the power of the apparatus to heat and ignite metallic 

 substances was augmented by enlarging the plates, without increasing their 

 number ; but that no increase of power to decompose water, or to produce the 

 shock, ensued. The calorific power, therefore, appeared to depend, cattris pa- 

 ribus, on the magnitude of the plates, while the chemical and physiological 

 power depended on their number. 



The battery of thirteen-inch plates was tried successively with pure water, 

 a solution of common salt, and dilute nitric acid. With water its effects were 

 feeble, with the solution of salt they were much more considerable, and were 

 still more energetic with nitric acid. With the last, three inches of iron wire, 

 yi^th of an inch in diameter, were rendered white hot, and two inches of the 

 same wire were fused. The action of the water, feeble as it was, was as- 

 cribed to the air and saline matter it held in solution ; and it was judged from 

 analogy that water perfectly purged of air and free from all saline substances, 

 would have no Voltaic action. A pile of thirty-six pairs of five-inch plates 

 lost its activity in an atmosphere of azote and hydrogen in about two days ; 

 and its power was constantly restored by common air, and rendered more in- 

 tense by oxygen gas. 



When two pieces of well-burnt charcoal, or a piece of charcoal and a me- 

 tallic wire, are connected with the apparatus an', immersed in water, on com- 

 pleting the circuit, gas was abundantly evolved, and the points of the charcoal 

 appeared red hot for some time after the contact was made. Sparks were also 

 produced by means of charcoal points immersed in concentrated nitre and sul- 

 phuric acids. When two charcoal points acted in water, the gaseous products 

 consisted of one eighth carbonic acid, one eighth oxygen, and one eighth in- 

 flammable gas, apparently hydrogen. The gases produced by a similar process 

 / from alcohol, ether, and dilute sulphuric acid, were also a mixture of oxygen 

 and hydrogen. In all these cases it appeared that the gases proceeded 

 chiefly from the decomposition of the water contained in the several solutions. 



The effects of the ignition of charcoal in muriatic acid confined over mer- 

 cury, were next tried. The charcoal being kept white hot for nearly two hours, 

 the gas was very little reduced in volume, and the charcoal was not sensibly [ 

 consumed. When the gas was examined, three fourths of it were absorbed by 

 water, and the remainder was inflammable.* 



* Davy's Works, vol. ii. ( p. 214. London, 1839. 



U 



