1824.] Conductors when transmitting the Electric Current. 175 



thus rendered strikingly sensible the electricity developed by a 

 mere difference in the state of the surface of two small portions 

 of copper wire from the same coil (one being a little cleaner than 

 the other) not above an inch in length of either being immersed; 

 or that set in motion by a copper and zinc wire held near toge- 

 ther and dipped in common pump water, powers which it is not 

 easy to render sensible by other means. For the success of 

 these experiments, however, it is not enough merely to plunge 

 the extremities of the conducting wires under sulphuric acid. 

 The surfaces of contact here require to be greatly increased,* so 

 as to insure the transmission of the whole of the electricity 

 developed. The best way is to immerse them in two consider- 

 able pools of mercury under the acid, one on either side of the 

 globule to be set in rotation. 



15. Hitherto we have considered only the effect produced 

 when a current of electricity is transmitted over mercury through 

 sulphuric acid. When other conducting liquids and other 

 metallic bodies are used, phaenomena of the same kind are pro- 

 duced, but so modified by the nature of the substances employed, 

 the intensity of the electric power, and the manner of conduct- 

 ing the experiments, as to become extremely perplexing ; and I 

 must warn the reader who may be inclined to repeat them, that 

 he must expect to find them frequently fail, or even give con- 

 trary results from those I shall describe, owing to causes by no 

 means easy to discover. The principal is impurity in the mercury 

 used, and none should be used but what has been carefully 

 distilled, and well washed with dilute nitric acid. It was long 

 before I discovered this necessity ; and ignorance of this essen- 

 tial condition engaged me in a series of tedious and dishearten- 

 ing repetitions of every experiment, till I was on the point of 

 relinquishing the subject in despair, encountering contradictory 

 results in operations conducted, as I then supposed, in a manner 

 precisely similar. 



16. When mercury, so purified and perfectly clean, is placed 

 in any conducting liquid, and the circuit completed without 

 bringing either pole in contact with the metal, the pha3nomena 

 vary with the nature of the liquid ; but, generally speaking, the 

 effect is the production of currents more or less violent, radiat- 

 ing from the point nearest the negative pole. In the acids, 

 particularly in the more powerful and concentrated ones, and 

 such as are good conductors of electricity, they are decided and 

 violent. In saline solutions their force is less, in proportion as 



* The efficacy of an increase of surface for transmitting electricity into a liquid is 

 remarkable. Hy bringing the positive pole in contact with a large surfacr of mercury, 

 or still better, of an amalgam of mercury and zinc, over which a saline solution is 

 poured, the reduction of the metafl of the alkalies and earths at the other pole is 

 operated with a degree of facility hardly to he imagined without trial. In this way the 

 decomposition of ammonia may be effected with three pair of single plates of the above 

 dimensions, in very moderate action. 



