504 Intelligence and Miscellaneous Articles. 



under all circumstances, even at temperatures below zero at which 

 the psychrometer will not serve. A determination takes fifteen 

 minutes. After finishing one, the apparatus can, without any 

 further preparation, be used for a second ; and once filling with 

 sulphuric acid suffices for many thousand determinations. Volume- 

 percentages are read off directly from the apparatus. For calcula- 

 ting percentages of volume into millimetres vapour-pressure the 



formula e=V —— is employed, in which V denotes the volumes, e 



and b the heights of the barometer. The same apparatus can also 

 be used for fog-measurement. For that purpose we warm the foggy 

 air a little, before it enters the volume-hygrometer, and then pro- 

 ceed as usual : we thus obtain the total amount of the aqueous 

 vapour, consisting of that which was present as such in the air and 

 possessed the maximum of tension, plus that which was first formed 

 by the volatilization of the fog vesicles. — E. W. in the Beibldtter zu 

 den Annalen der Physih und Ohemie, 1879, No. 7, p. 485* 



ON THE GALVANIC OXIDATION OF GOLD. BY M. BERTHELOT. 



Grotthuss, in his classic experiments on the decomposition of 

 water by the galvanic pile *, remarked the solution of a gold wire 

 employed as the positive pole in sulphuric acid traversed by the 

 current. This interesting fact was pointed out to me by our vene- 

 rated dean, M. Chevreul, who asked me if such an effect might not 

 be due to the formation of persulphuric acid. It was for the purpose 

 of replying to his question that I made the following experiments. 



I first repeated Grotthuss's experiment, which is precisely as he 

 described it. The sulphuric acid (at 10 per cent.) becomes yellow 

 and rapidly dissolves the gold wire : the dissolved gold can easily 

 be detected by means of stannous chloride. A portion is repreci- 

 pitated upon the negative pole. 



Nitric acid, under the same conditions, equally attacks gold, and 

 becomes filled with a violaceous precipitate (gold or aurous oxide ?), 

 which remains in suspension. 



Dilute phosphoric acid, on the contrary, does not appreciably 

 attack gold, even under the influence of the galvanic current; nor 

 has potass any greater action. 



That gold is attacked by sulphuric and nitric acids is not due to 

 ozone ; for oxygen charged with ozone remains without action upon 

 gold in the presence of water, whether pure or charged with sul- 

 phuric or nitric acid. 



Nor does persulphuric acid (prepared by electrolysis) attack gold, 

 even if it contains in addition a portion of oxygenated water. 



It follows from these observations that the attacking of gold 

 takes place solely under the influence of the galvanic current and 

 at the contact of the electrode with the electrolyzed liquid. — 

 Oomptes Rendus de VAcademie des Sciences, Oct. 27, 1879, p. 683. 

 * Annates de Ctiimie, t. lxviii. p. 60. 



