GALVANISM. 



It will appear from the above experi- 

 ments, that the galvanic phenomena are 

 essentially promoted, by having two me- 

 tallic surfaces so situated that one shall 

 be oxydated, and that the other shall be 

 situated as near it as possible, for the 

 purpose of receiving 1 its electricity. We 

 have shewn, that the current is not 

 only interrupted by distance, but that it 

 is essential the passage should be a direct 

 line. 



In Dr. WoHaston's experiments, when 

 the wires were placed in a metallic solu- 

 tion, such as that of copper and silver, 

 and the contact formed between the zinc 

 and silver wires, no hydrogen was evolv- 

 ed by the latter, the contrary of which 

 was the case with the dilute acid ; but the 

 metal in solution became reduced upon 

 the silver. 



There does not appear any thing mys- 

 terious in the reduction of the metal, 

 since the hydrogen does not appear, be- 

 ing employed in the deoxydation of the 

 metal. A further proof that this is the 

 case is, that no other metals can be re- 

 duced in this way but such as do not de- 

 compose water. This singular process 

 enables us to account for several facts 

 which have hitherto appeared anomalous. 

 If a glass plate be smeared over with a 

 solution of nitrate of silver, and a com- 

 mon pin be laid in the middle of the plate, 

 beautiful ramifications of metallic silver 

 will soon appear, as if vegetating from 

 the pin. If the process be examined by 

 a magnifying glass, the ramifications of 

 silver may be fairly seen to grow from 

 their ends. Though the more oxydable 

 metal, the pin, may, in the first instance, 

 have reduced a portion of silver, it does 

 not account for the vegetative appear- 

 ance which is afterwards observed. The 

 pin cannot reduce the silver at so great a 

 distance from itself, which is sometimes 

 more than an inch In order to prove, 

 that the agency of the oxydable metal 

 was not essential to the reduction of the 

 metal, the writer of this article covered 

 one half of the plate with liquid nitrate 

 of silver, and the other half with dilute 

 muriatic acid, suffering the liquids to 

 touch each other; a wire of zinc was 

 laid in the dilute acid, and one of pla- 

 tina in the nitrate of silver. As soon 

 as the opposite ends of the wires were 

 brought in contact, beautiful ramifica- 

 tions of silver soon began to appear 

 from the platina wire, but no gas was ob- 

 served. 



If a solution of gold be used, instead of 

 that of silver, the platina becomes spee- 

 iily gilt. The experiment producing 



what is called the lead-tree cannot be 

 accounted for in any other way : it con* 

 sists in filling a bottle with a solution of 

 acetate of lead, in the upper part of 

 which is suspended a piece of metallic 

 zinc : in the course of a day or two, me- 

 tallic lead is observed in shining filaments, 

 suspended from the piece of zinc. The 

 same difficulty occurs in this as in the 

 last experiment : the filaments of lead 

 constantly grow from the ends at a dis- 

 tance of many inches from the zinc. In 

 order to prove that this experiment is 

 similar to the last, that is, that the lead is 

 reduced by the hydrogen, take a tube, A 

 B, fig. 3, at one end of which tie a piece 

 of bladder so tight that the tube may hold 

 water; let a cork be inserted at A, 

 through which the platina wire, P p, Is 

 passed ; the tube being set upright in 

 the zinc cup, D, containing dilute muria- 

 tic acid, and a connection formed at P, 

 the platina soon becomes covered with 

 brilliant crystals of metallic lead : hence 

 it would appear, that the platina had the 

 power of reducing the lead into its me- 

 tallic state, or that some substance had 

 been transmitted through the bladder 

 adequate to that effect. If, instead of 

 the acetate of lead, the tube be filled 

 with dilute acid, upon the connection be- 

 ing formed at P, the platina becomes co- 

 vered with bubbles of hydrogen : need 

 we, therefore, hesitate in concluding, 

 that the lead owes its reduction to the 

 hydrogen ? 



The method of whitening brass and 

 copper, by boiling them with cream of 

 tartar and tin, is a process of this kind ; 

 the cream of tartar, and the metallic tin, 

 answering the purpose of the zinc and 

 acetate of lead in the last experiment : a 

 portion of the tin in solution is reduced 

 upon the copper or brass, rendering it 

 white by the hydrogen which is produc- 

 ed during the galvanic contact of the 

 copper or brass with the tin. 



In all the experiments, the zinc wire is, 

 during its contact with that of the pla- 

 tina, silver, &c. undergoing an increased 

 oxydation, which is proportionate to the 

 quantity of hydrogen evolved at the pla- 

 tina wire ; since the oxygen of that and 

 hydrogen, both of which are derived 

 from the water, are disposed of in the 

 oxydation of the zinc. The hydrogen 

 passes from the zinc to the opposite wire, 

 with the greatest facility, through a di- 

 rect liquid communication, the shorter 

 the better. It becomes much interrupted 

 by having to turn sharp angles, or in pass- 

 ing through small apertures. It passes 

 with more or less freedom through solid 



