RECENT PROGRESS IN PHYSICS. 411 



The sodium, liberated by the decomposition of the chloride of sodium, 

 combines with the chlorine of the chloride of silver, and thus the 

 silver is reduced and obtained in a more or less porous condition. It 

 is the more compact as the current is weaker, i. e., as the solution of 

 salt is more dilute, and as tlie aperture closed with the clay stopper is 

 smaller. But tlie action had, in all cases, to be continued for several 

 weeks, in order to reduce only a moderate quantity of silver. But 

 here, too, Becquerel was not the first to describe this, or, at least, a 

 very similar methcd. The instrument maker and. assayer, Oechsle, 

 in Pfarzheim, had, in 1842, already published in Dingler's Journal, 

 vol. 86, the following method of reducing chloride of silver: The 

 chloride is worked into a thick paste with a saturated solution of 

 common salt, and then put into a porous cell, which is set in a vessel 

 containing sulphuric acid diluted to ^Lj the zinc is placed in this ves- 

 sel, while platinum or silver is used with the chloride of silver, and 

 the circuit is kept closed until the grayish sediment of silver, when 

 stirred no longer, shows any milky streaks ; it is then well washed 

 and dried. A similar process is again described in Poggendorf's 

 Annals, 1848, No. 11. 



James Napier (Dingler's Journal, vol. 97, from Repertory of Patent 

 Inventions, July, 1845,) proposes to reduce the metals in a fused 

 state, and this he does by putting the roasted metallic sulphurets 

 together with the proper flux in a black lead crucible, which, with 

 the exception of the bottom, had been coated inside with clay. When 

 all is fused he places upon the mass an iron plate riveted to a rod of 

 the same metal, another iron rod is to be placed in contact with the 

 outer surface of the crucible, and both rods connected with the proper 

 poles of a battery. 



William liitchie, in 1844, patented a process for obtaining metallic 

 copper, which is very similar to that described by Dechaud and 

 Gautier de Claubry in the Comptes Rendus of 1845, (Dingler's Jour- 

 nal, vol. 97.) It consists essentially in changing the sulphuret into 

 sulphate of copper, which is then decomposed by galvanism. The 

 apparatus for this purpose consists of a number of large troughs with 

 several divisions, each of which is again divided into two parts by a 

 pasteboard diaphragm. One of these parts contains sulphate of copper 

 and a plate of lead, or rather of sheet iron coated with lead ; tlie other 

 contains sulphate of iron and a cast iron plate, which, together, form 

 a simple battery. The inventors think that they will be able for 

 every square metre of plate to reduce 1 kilogramme of copper in 

 twenty-four hours, and that of the whole quantity of copper in the 

 solution they can obtain 50 per cent, in plates, 25 per cent, granu- 

 lated, and the remainder in a finely divided state. The apparatus is 

 supplied from large reservoirs containing the liquids in the proper 

 state of concentration, while the exhausted solution of sulphate of 

 copper, as well as the saturated solution of the sulphate of iron, are, 

 at the same time, carried off. Accurate statements as to the advan- 

 tages of this process are still wanting. 



[Since the date of the })ublication of Miiller's report the art of elec- 

 trotyping has been greatly developed. The general principles of this 

 art, so well shown by our author, are so universally applicable that 



