GALVANISM. 



elements, oxygen and hydrogen. The 

 discovery of this fact is due to the united 

 researches of the late Mr. Nicholson and 

 of Mr. (now Sir Anthony) Carlisle, and 

 was one of the immediate consequences 

 of the invention of the pile by Volta. 



(45.) The most convenient mode of 



exhibiting the decomposition of water by 



galvanism is to fill with water a glass 



tube, (see/0-. 17.) to each end of which 



Fig. 17. 



a cork has been fitted so as to confine 

 the water, and to introduce into the tube 

 two metallic wires, by passing one at 

 each end through the gork which closes 

 it, allowing the extremities of the wires, 

 that are in the water, to come so near 

 each other as to be separated by an in- 

 terval of only a quarter of an inch. The 

 wires being then respectively made to 

 communicate with each of the two poles 

 of a voltaic batteiy, the following phe- 

 nomena will ensue. If the wire con- 

 nected with the positive pole of the bat- 

 tery consists of an oxidable metal, it is 

 rapidly oxidated by the water surround- 

 ing it while at the same time a stream 

 of minute bubbles of hydrogen gas arises 

 from the surface of the other wire, which 

 is in connection with the negative pole. 

 But if we employ wires made of a metal 

 which is not susceptible of oxidation by 

 water, such as gold or platina, gas will 

 be extricated from both the wires, and 

 by means of a proper apparatus may be 

 collected separately. This may be ac- 

 complished by taking two glass tubes, or 

 receivers, closed at one end, and filled 

 with water; this fluid is retained by 

 inverting them over a sufficient quantity 

 of water contained in a glass vessel, as 

 js shown in Jig. 1 8. Each tube is to be 



furnished with a platina wire, P andN, 



passed through the closed extremity, 

 and descending within it through its 

 whole length. The open ends are then 

 to be placed as near to each other as 

 their position in the water will allow ; 

 and the wires are to be connected re- 

 spectively with the opposite poles of a 

 voltaic battery. Gas will immediately 

 be seen to rise from each of the wires, 

 but in different quantities. The tube 

 containing the negative wire, N, will be 

 soon filled with hydrogen gas, while the 

 other, which is traversed by the positive 

 wire, P, will, in an equal time, be only 

 half filled with oxygen gas. This arises 

 from the circumstance that the volumes 

 of the two gases, which form water when 

 combined, or which are the products of 

 the decomposition of water, are in the 

 above proportion ; that is, the volume 

 of the hydrogen is to that of the oxygen 

 gas as two to one. That the water is in 

 this experiment perfectly resolved into 

 its two elements is satisfactorily proved 

 by mixing together the gases thus ob- 

 tained, and firing the mixture by the 

 electric spark ; when the whole instantly 

 loses its gaseous form, and is reconverted 

 into water. 



(46.) If the water employed in the 

 preceding experiment be not perfectly 

 pure, other substances besides oxygen 

 and hydrogen will also make their ap- 

 pearance at the two wires, and the 

 apparent formation of such substances 

 from water was the occasion of great 

 perplexity to the earlier experimentalists. 

 But Sir H. Davy succeeded in proving, 

 by a most masterly train of investigation, 

 that when every precaution is taken to 

 ensure the purity of the water subjected 

 to the operation of galvanism", the only 

 products obtained are the two gaseous 

 elements of water, oxygen, and hy- 

 drogen. 



(47.) In these experiments it became 

 manifest, that under the influence of vol- 

 taic electricity neutral salts, existing in 

 any solution, were decomposed, the acid 

 portion being accumulated around the po- 

 sitive wire, on the same points where the 

 extrication of oxygen took place ; while 

 the bases, whether earthy, alkaline, or 

 metallic, were, at the same moment, 

 transferred along with the hydrogen to 

 the negative wire. The best mode of 

 exhibiting these decompositions, is to 

 employ two cups, made either of glass, 

 or, where great precision is requisite, of 

 agate, or of gold ; the liquids contained 

 in these cups being connected together 

 by a few fibres of moistened asbestos, 



