1832.] Progress of European Science. 



369 



M. Becquerel perceived that one way to preserve electrical effects sensibly 

 constant during a certain interval, in a voltaic element formed of two metals, 

 was to prevent their surfaces from becoming covered with solid deposits : unfor- 

 tunately the process he adopted to obviate this defect is not of easy application 

 in the ordinary construction of the pile, nor is it explained in the report. 



Before entering upon the processes of electro-chemistry that he has employ- 

 ed to produce new chemical combinations, he describes an old experiment by 

 Bucholz, founded on the same principles. 



Bucholz, having introduced into a narrow receiver, containing a solution of 

 sulphate of copper surmounted by plain water, a plate of copper, so that its upper 

 part was immersed in the water, and the lower part in the sulphate, observed, 

 that this part became soon encrusted with metallic copper : M. Becquerel sup- 

 poses that, in this case, the two liquids form a voltaic couple, of which the solu- 

 tion is the positive pole and the water the negative. 



When the slip of copper is immersed, a current of positive electricity is esta- 

 blished from below upwards ; thus the plate becomes a pile of which the base is 

 negative, and the summit positive ; and as a simple consequence, the copper is 

 transported to the negative pole. 



The possibility of thus establishing piles of single pairs formed either of two 

 solids, or of two liquids, — and the property enjoyed by oxigen of travelling quicker 

 than do the acids to the positive pole of these piles, which have always a very 

 feeble tension, — led M. Becquerel to avail himself of electro-chemistry, to ob- 

 tain several compounds of a remarkable nature, whether from their resemblance 

 to the natural products met with in the strata of the earth, or from their similarity 

 to certain products of the chemist's laboratory. As an example, 



He put into a closed tube some concentrated muriatic acid, and a piece of 

 charcoal fixed to a slip of silver by a wire of the same metal ; the open end of the 

 tube was then drawn out to a fine thread with the blowpipe, but not closed. At the 

 end of several months, there were formed upon the lamina of silver, octohedric 

 ciystals of chloride of silver, 0.0 01 metre (0.04 inch) in diameter, which resem- 

 bled exactly those of nature ; while from the charcoal was disengaged some gas 

 supposed to be carburetted hydrogen. The rationale is as follows : the charcoal 

 and the silver form together a pile, of which the former is the negative pole; hence 

 the hydrochloric acid is decomposed, — the chlorine goes over to the silver with 

 which it combines, while the hydrogen goes to the negative pole. When copper is 

 substituted for silver, protochloride of copper is deposited in tetrahedric crystals. 

 Protoxides of copper, of lead, the oxide of zinc, &c. have all been obtained 

 in crystals by the following process : taking copper as an example : in a glass 

 tube, a convenient portion of deutoxide of copper is placed, and a saturated 

 solution of nitrate of copper, along with a slip of the same metal which ought to 

 touch the deutoxide. The tube is then hermetically sealed ; the nitrate in contact 

 with the deutoxide gradually passes to the state of insoluble subnitrate : then the 

 lower part of the solution being less charged than the upper, acquires negative 

 electricity, whilst the upper becomes positive ; a current commences therefore from 

 above downwards, so that the lamina is itself a pile, of which the positive pole is 

 below, and the negative above. It is natural, therefore, that the protoxide of cop- 

 per should transport itself and crystallize on the upper extremity of the lamina. 



Finally, M. Becquerel has formed double chlorides, bromures, iodures, sulphu- 

 rets and cyanurets, crystallized under the influence of electro-chemical forces. 

 Thus to obtain a double chloride of copper and sodium, he takes a tube curved 



2 A 2 



