TRKATMI-NT OF OK) 241 



whereas the oxidisable metals were placed iu a porous cell 

 filled with salt water. By grouping six simple baths so as to 

 constitute a real battery of six cells, the chloride decomposed 

 more rapidly without any increase of expenditure. In the first 

 few hours three parts of the silver are extracted, the extraction 

 of the remainder requiring a much longer time. This is due 

 to the liquid, which becomes more resistant, and to the electric 

 current, which decreases in strength. 



For the treatment of copper ores Becquerel transformed 

 the sulphides into sulphates with or without the assistance of 

 sulphuric acid ; the sulphate once obtained, was placed in a 

 concentrated solution and submitted to the action of the electric 

 current. More frequently he adopted the simple bath arrange- 

 ment, using cast iron as a positive electrode ; to this effect, he 

 superposed two solutions in the same vessel, one saturated with 

 denser sulphate of copper, the other with lighter sulphate of 

 iron ; in the first he introduced a copper strip, and in the 

 second a cast-iron strip, communicating with the other strip by 

 means of a metallic conductor. The couple resulting from that 

 arrangement was sufficiently powerful to decompose the sul- 

 phate of copper ; the oxygen and the acid of the sulphate were 

 deposited on the cast iron forming sulphate of iron, whereas the 

 copper was deposited on the copper strip. 



This operation had a serious inconvenience; the deposited 

 copper was first in a state of chemical purity, then it became 

 brittle, friable, and charged with iron ; in order to prevent 

 these irregularities Becquerel conceived an apparatus which is 

 worth describing in detail. 



It consisted of a wooden case, lined with lead covered with 

 wax, and intended for receiving the solution of sulphate of 

 iron. This case was provided with two openings, the top one 

 for the introduction of the normal liquor, the lower one for 

 the expulsion of the too dense liquor by means of siphons. 

 Some leaded sheet-iron boxes were immersed in the interior of 

 this case, the end walls and bottom of which boxes were of 

 metal, and the lateral walls of openwork lined with sheets of 

 cardboard. An opening at the bottom admitted, by means of 

 siphons, the concentrated solution of sulphate of copper, and 



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