48 



ELECTRICITY. 



order to prevent its being broken by the 

 discharge. Electrical shocks were then 

 passed between the two ends of the 

 wires through the water in the tube by 

 means of a Leyden jar, which had a 

 square foot of coated surface. This jar 

 was charged by a very powerful double 

 plate machine, which caused it to dis- 

 charge twenty-five times in fifteen revo- 

 lutions. At each explosion bubbles of 

 air were formed, and rose to the top of 

 the tube. As soon as a sufficient quan- 

 tity had collected to leave the upper end 

 of the wire uncovered by the water, so 

 that the shock had now to pass through 

 a portion of the mixed gases, they were 

 instantly kindled ; a reunion of the ele- 

 ments took place ; water was again form- 

 ed, and the space they had occupied was 

 immediately filled with fluid from below, 

 so as to restore every thing precisely as 

 at the outset of the experiment. It was 

 ascertained by the most decisive che- 

 mical tests, that the gases thus obtained 

 consisted of a mixture of oxygen and 

 hydrogen gases. 



(176.) It may appear somewhat para- 

 doxical that the same agent should, in 

 the course of the same experiment, pro- 

 duce at one time decomposition, and 

 at another combination of the same ele- 

 ments. The simplest way of reconciling 

 this apparent discordance, is to suppose 

 that the combination of the gases is the 

 effect of the heat evolved during its 

 forcible transit through an aeriform 

 fluid that opposes' considerable resistance 

 to its passage ; while the decomposition 

 of the liquid is the direct consequence of 

 the agency of electricity when not inter- 

 fered with by heat. 



(177.) Until lately, it was thought ne- 

 cessary to employ powerful machines 

 and large jars in order to effect the de- 

 composition of water by electricity, and 

 that mere sparks from acommon.machine 

 were inadequate to accomplish this pur- 

 pose. That there is in this respect, how- 

 ever, no essential distinction in the ope- 

 ration of these two forms of electricity 

 has been satisfactorily shown by Dr. 

 "Wollaston. This distinguished philos<5- 

 pher, perceiving, with his accustomed 

 sagacity and penetration, that the de- 

 composition would depend on duly pro- 

 portioning the strength of the charge to 

 the quantity of water, and that the quan- 

 tity exposed to its action at the surface 

 of communication depends on the extent 

 of that surface, inferred that by reducing 

 the surface of communication the de- 

 composition of water might be effected 



by smaller machines, and with less pow- 

 erful excitation than had hitherto been 

 applied to this object. Having procured 

 a small wire of fine gold, and given to it 

 as fine a point as possible, he inserted it 

 into a capillary glass tube; and after 

 heating the tube, so as to make it adhere 

 to the point, and cover it in every part, 

 he gradually ground it down, till, with 

 a pocket lens, he could discern that the 

 point of the gold was exposed. When 

 sparks from a prime conductor of an 

 electrical machine were made to pass 

 through water by means of a point so 

 guarded, a spark, extending to the dis- 

 tance of one-eighth of an inch, would 

 decompose water when the point ex- 

 posed did not exceed one 700th of an 

 inch in diameter. With another point, 

 estimated at one 1500th, a succession of 

 sparks one-twentieth of an inch in length 

 afforded a current of small bubbles of 

 air. With a still finer filament of gold, 

 the mere current "of electricity, without 

 any perceptible sparks, evolved gas from 

 water. 



(178.) When a solution of sulphate of 

 copper was subjected to the action of 

 electricity by means of these slender 

 conducting wires, the metal was revived 

 around the negative wire; but upon 

 reversing the direction of the current of 

 electricity, so that the same wire now 

 became positively electrified, the copper 

 which had collected around it was re- 

 dissolved, and a similar precipitate was 

 deposited on the opposite wire, which 

 was now the negative one. Similar ex- 

 periments made with other metallic 

 solutions were attended with analogous 

 results ; the negative wire always sepa- 

 rating oxygen from its combinations, 

 the positive wire always attracting it, 

 and effecting its union with the bases 

 presented to it. With solutions of neu- 

 tral salts, the alkaline or earthy bases 

 were attracted by the negative, while the 

 acids were attracted by the positive wire. 

 The experiments of Sir Humphry Davy 

 have confirmed these results as far as 

 concerns the chemical action of common 

 electricity ; Jbut as this is a subject which 

 bears more immediate relation to che- 

 mistry and to galvanism, it would not 

 be right to enlarge upon it in the present 

 treatise. 



(179.) The magnetic effects of elec- 

 tricity will likewise form the subject of a 

 distinct treatise, as they now constitute 

 a new branch of science, under the title 

 of ELECTRO-MAGNETISM, 



