Intelligence and Miscellaneous Articles. 155 



last partly reduce the chloride of silver, and also act upon it by double 

 decomposition. 



The arseniurets, sulpharseniurets and sulphantimoniurets, placed 

 in the same circumstances, produce upon the chloride of silver an 

 action resembling that of the sulphurets. 



These different bodies were added to chloride of silver dissolved in 

 ammonia, and sometimes in hydrosulphite of soda ; but it was found 

 that the presence of the solvent produced no other effect than that 

 of accelerating the phsenomenon, and rendering observation of it more 

 commodious, but it did not alter the essential conditions of it. 



It is remarkable to observe that the decomposition produced by 

 the sulphurets, arseniurets, &c., is often as complete as if the opera- 

 tion was conducted on bodies dissolved in water. As examples of this 

 may be cited, native sulphuret of copper, arseniuret of antimony, 

 arsenical cobalt, arsenical nickel, &c. Certain sulphurets, though but 

 few, do not act ; such for example are the sulphuret of mercury and 

 gray cobalt, which in this respect differs much from gray nickel. 

 Metallic iron resembles it^in this respect, that it does not precipitate, 

 or but very slightly, silver from solution in the form of concentrated 

 ammoniacal chloride, or even in the form of nitrate. 



The power of sulphurets to decompose chloride of silver is gene- 

 rally more marked in those which act by way of reduction than in 

 those which produce double decomposition ; moreover this power 

 appears to have relation to the electro-chemical state of the metals. 

 It must also be added, that various minerals belonging to the same 

 species possess decomposing powers varying according to their dif- 

 ferent composition, crystalline form, density and cohesion. 



Bromide of silver, put into contact with metallic sulphurets, offer 

 the same phsenomena of decomposition as the chloride. In short, all 

 these facts appear to depend upon a general law of the reactions of 

 the sulphurets on the chlorides, and of insoluble on soluble salts. 

 Moreover, the authors find that these reactions are produced in the 

 dry as well as in the humid way : thus galena decomposes chloride 

 of silver in fusion ; blende was found to detain the vapour of this 

 chloride and to convert it into sulphuret of silver. The same vapour 

 is also decomposed with the assistance of heat by quartz, felspar, 

 argil and silicates in general. 



The reactions of sulphurets on chlorides, produced under such va- 

 rious circumstances, evidently possess a general character, and the 

 observation of various metalliferous deposits offers additional confir- 

 mation of it ; for the chloride and bromide of silver do not occur 

 among the same metallic sulphurets, but in the upper parts of veins, 

 which have been altered and oxidized by the influence of external 

 causes. The authors also deduce from their experiments, the ex- 

 planation of certain geological phsenomena ; for example, the con- 

 centration which the mineral of native and sulphuret of silver of the 

 veins of Konigsberg has undergone ; a mineral which occurs agglo- 

 merated by schistose bands impregnated with various metallic sul- 

 phurets, as iron and copper pyrites, blende and galena. — Comptes 

 Rendus, Decembre 10, 1849. k 



