ELECTRICITY. 



501 



Effects of 

 electricity 

 in restoring 

 oxides to 

 the metal- 

 lic state. 



Effect of 

 electricity 

 in decom- 

 posing 

 fluids. 



PLATE 

 crxi.vi. 



Fig.8. t 



Kxjx-ti- 



mtr,t> nf 

 Or Pear- 

 ion. 



charges; but Mr Singer lias found that more moderate 

 charges, from a large battery, are sufficient. He seems 

 to think that the law given by Mr Brooke for the 

 fusion of wires, is true also of their oxidations; for he 

 found that a battery of 40 square feet of coated sur- 

 face, charged with 10 grains, will oxidate the same 

 quantity of gold wire as a battery of 20 feet charged 

 to 20 grains. Mr Singer has, in some copies of his 

 work, given specimens of the oxides of gold and copper. 



Along with the power of oxidating metals, electricity 

 possesses also the faculty of revivifying metallic oxides, 

 or restoring them to the metallic state. This curious 

 property was discovered by Beccaria. By sending the 

 explosion of a jar between two pieces of the calces, he 

 revivified the oxide of zinc, and even produced quick- 

 silver from cinnabar. The best way of making these 

 experiments is to place the oxide in a glass tube, and 

 make it occupy about half an inch of the lower sur- 

 face of the tube, when it is placed horizontally on the 

 table of Henley's discharger. Several strong charges 

 being sent successively through the tube, the revived 

 metal will adhere to its surface. By means of a jar of a 

 very moderate size, vermilion may be separated from 

 the mercury and sulphur which compose it. 



The decomposition of water by the electric spark, 

 was first performed by MM. Pacts, Van Troostwyk, and 

 Deiman, with the assistance of Mr Cuthbertson. They 

 employed a machine consisting of two plates 31 inches 

 in diameter, which had the power of making the jar 

 discharge itself 25 times in 15 revolutions. The ap- 

 paratus which they employed consisted of a glass tube 

 DE, Plate CCXLVI. Fig. 8, 12 inches long, and ith 

 of an inch in diameter. It was hermetically sealed at 

 the end D ; but before it was sealed, a gold or platina 

 wire D d, l\ inch long, was introduced within the tube, 

 and fixed at D, by melting the glass around it. Ano- 

 ther platina wire, or a gold wire with platina at its ex- 

 tremity, as E e, was introduced at the open end E of the 

 tube, and carried up to e, within .Jth of an inch of the 

 extremity d of the upper wire. The tube DE was now 

 filled with distilled water, which had been freed from 

 air by one of Cuthbertson's best air pumps. The open 

 end E of the tube was immersed in a vessel V contain- 

 ing quicks jjver, and a little common air was let into 

 the convex part of the curved end of the tube, in order 

 to prevent it from being broken by the electrical dis- 

 charge. The upper extremity D of the wire D d was 

 then brought into contact with an insulated brass ball 

 C, placed at a little distance from the prime conductor 

 AB of the electrifying machine. The lower wire E e, 

 immersed in quicksilver, communicated with a chain 

 VG, which was connected with the exterior coating of a 

 Leyden jar, but which contained about a square foot, or 

 144 square inches, of coated glass, and had its ball H in 

 contact with the prime conductor AB. When the ball 

 C was in contact with the conductor AB, the electrical 

 discharges did* not disengage any gas from the distilled 

 water, but upon increasing its distance, a position was 

 found where the gas was disengaged, the gas ascending 

 immediately to the top of the tube. By continuing the 

 electrical discharges, gas was evolved till it reached to 

 near the lower extremity of the upper wire, and then a 

 discharge made the whole gas disappear, its place being 

 supplied with water. 



In the preceding method, which is tedious and la- 

 borious, a part of the charge only passes from the one 

 wire to the other, at each explosion, on account of the 

 imperfect conducting power of the water, the electricity 

 remaining in the Leyden jar being nearly one half. Dr 



Pearson, who, after great labour, succeeded in decom- Besptive 

 posing water by electricity, made use of another me- 

 thod, which differs only from the preceding in the con- 

 struction of the tube DE. Dr Pearson fixed a glass 

 tube DE, Plate CCXLVI. Fig. 9, 4 or 5 inches Icng, PLATE 

 and f th or ^th of an inch in diameter, into the end of a CCXLVI. 

 brass tube EF, and he placed the wire at the top D, as ** 9> 

 formerly described, making it extend to the brass tube, 

 so as to be almost in contact with it when the explo- 

 sion is made. Care must be taken, however, to prevent 

 the wire from touching the tube, for in this case no gas 

 will be evolved. The tube being filled with w~ater, and 

 set in a cup of the same fluid, may be applied to the 

 conductor, as already described ; the insulated ball, 

 however, must be placed at a greater distance from the 

 prime conductor, and with a jar of only 50 inches of 

 coated surface, gas will be produced in the brass tube 

 at each discharge, in greater quantities, and with much 

 less trouble than in the apparatus of the Dutch che- 

 mists, in consequence of there being no electricity left 

 in the jar after each discharge. 



Mr Cuthbertson invented another verv simple ap- Mr Cuth- 

 paratus, shewn in Plate CCXLVI. Fig. 10. where DE bcrtson's 

 is a glass tube, 5 inches long, and half an inch wide, a PP ar 

 blown funnel-shaped at the end A. The other end PI.ATE^ 

 has a wire of an inch thick sealed into it, as for- p^ X J' V I- 

 nierly described, and extending nearly to the bottom of 

 the brass dish V, (generally within ^5. of an inch of it,) 

 on which the tube rests. The coated surface of the jar 

 requires to be about 150 inches, and the distance of the 

 brass ball C from the conductor A was about ^' 5 fh of 

 an inch. From experiments made with these instru- 

 ments, Dr Pearson concluded, that the gas evolved 

 from water consisted of oxygen and nitrogen, or azotic 

 gas. 



The apparatus for decomposing water was greatly Wpllaston'st 

 simplified by Dr Wollaston. This ingenious philoso- ^/ 

 pher inserted two finely pointed wires, made either of po 

 gold or platina, into capillary tubes. Each wire was ter. 

 introduced into the tube till it nearly reached the 

 end of it, and the glass was softened by he.it till it ad- 

 hered to the point of the wire, and covered it. The 

 glass was then gradually ground away, till the point of 

 the wire could be seen through a magnifying lens. One 

 of these wires communicating with the ground, or with 

 the negative conductor of the machine, and the other 

 with an insulated ball placed near the positive conduc- 

 tor, the two points were placed near each other in a 

 vessel of water; when a current of sparks is discharged 

 through the wires, a series of minute bubbles of gas 

 rise from the points of the gold wires, and, when col- 

 lected in an inverted receiver, they explode on the ap- 

 plication of a lighted taper. Dr Wollaston found by 

 experiment, that a point -r^th of an inch in diameter, 

 decomposed the water when the spark which passed 

 from the conductor to the insulated ball was ^th of an 

 inch in length ; and that a point TjVtf tn ^ an * nc ' 1 *" 

 diameter, produced a similar effect when the sparks 

 were only ^th of an inch in length. Hence the rapi- 

 dity of the decomposition was proportional to the limit- 

 ed size of the point of the wire. We are indebted also Experi- 

 to Dr Wollaston for the following interesting experi- ments of Dt 

 ments with the preceding apparatus. Having trans- 

 mitted a current of electric sparks, by means of two 

 fine gold points, along the surface of a moistened card 

 tinged with litmus, and placed between the points, a 

 redness appeared about the positive wire after a few 

 turns of the machine. By placing the negative wire 

 upon the red spot, it was soon restored to its original 



