Chemistry and Physics. 219 



of its temperature, although the action at first appears to he 

 materially influenced by these conditions. — Zeitschr. Electrocliem. y 

 iii, 424-5, April, 1897. G. f. b. 



3. On the Use of the Copper Voltameter. — Additional experi- 

 ments have been made by Foerster upon the copper voltameter 

 and the best means of avoiding the errors to which it is liable. 

 While the copper sulphate solution should be concentrated in 

 order to avoid the deposition of the metal in the pulverulent 

 form, yet it increases the concentration of the cuprous ions; 

 although, owing to their oxidation by the air, the solution never 

 becomes saturated with these ions. Hence when the solution is 

 exposed to the air the quantity of copper deposited is too small, 

 particularly when the current density is small. The fact that a 

 copper plate in an acid solution of copper sulphate is most 

 strongly attacked at the surfaee of the liquid, is thus explained. 

 If sulphuric acid be added to the copper sulphate solution, while 

 it diminishes to some extent the concentration of the cuprous 

 ions, its presence is of much more importance in preventing the 

 separation of cuprous oxide, which, owing to the hydrolysis of 

 cuprous sulphate, takes place in neutral solutions. If this cuprous 

 oxide be deposited on the cathode, it not only increases the 

 weight of the deposit but it causes inequalities in conductivity 

 and hence gives rise to the production of cuprous ions where the 

 current deusity is smallest. Again, a saturated sulphate of cop- 

 per solution cannot be used because the solubility of this salt is 

 diminished by the presence of the acid and hence causes the 

 deposition upon the anode of the salt itself, producing an increase 

 in resistance. He recommends as a suitable solution, one contain- 

 ing 125 grams of CuS0 4 (H 2 0) 5 and 50 grams of H 2 S0 4 to the 

 liter. When air is present no more copper is dissolved by the 

 strongly acid solution than by the weaker one ; a normal solution 

 of copper sulphate, normal also as to the sulphuric acid, dissolv- 

 ing 17 milligrams of copper, while a solution containing only one 

 thousandth of an equivalent of acid, under the same conditions, 

 dissolved 15 milligrams. For very weak currents the author uses 

 a closed voltameter containing a solution oi copper sulphate, one- 

 tenth or even one-twentieth of a gram-equivalent, and one gram- 

 equivalent of sulphuric acid ; a slow current of pure hydrogen 

 being continuously passed through it. This reduces to a mini- 

 mum the formation of cuprous ions, while their conversion at the 

 anode into cupric ions is prevented by enclosing this anode in 

 parchment paper. The author states that the maximum current 

 density for obtaining an adherent copper deposit is higher the 

 greater the concentration of the solution and the more completely 

 local dilution is prevented by stirring. In the case of a normal 

 solution of copper sulphate and sulphuric acid, a current ot 2 

 amperes per square decimeter is not too great. No advantage 

 results from measuring the loss of the anode to determine current. — 

 Zeitschr. Electrochem. ,'iW, 479-482, 493-497, May, 1897. G. f. b. 



