30 PRECIPITATIOK OP OXIDES BY THETR OWN METALS. 



tal fiotn its solution, which I will examine when 1 have lei- 

 sure, unless I am prevented by others. 



Addition to the preceding paper. 



The results I have farther to remark, that the results of my experi- 



ments on the precipitation of copper confirm an observation 

 announced by Mr. Buenger; but for more certainty I made 

 the following experiment. 



Farther exp. ^l. T formed a chain by putting into a cylindrical vessel 



with sulphate , . p, r 1 1 . !> • • 



•f copper. a solution or two ounces or sulphate oi copper in six ounce* 



of boiling water, on this I poured six ounces of water, and I 

 immersed in the two liquids a slip of copper. At the expir- 

 ation of 24 hours no change appeared on the slip of copper, 

 either in the cupreous solution, or in the water. Some sul- 

 phate of copper however was separated, and the two liquors 

 were well mixed. 

 Saiphate of 22. 1 repeated the former experiment exactly, except 



4ii^t«d^ water! *^^^ ^ added an eighth of sulphuric acid to the water era- 

 ployed. The result was, as soon as the chain was formed 

 an oxidation and disoxidation of the metal took place, and 

 a point of 0, 1 of a line broad, formed on the slip of copper. 

 At the expiration of 48 hours, as the action no longer in- 

 creased at the two poles, I took out the slip of copper, and 

 found, that the whole of the part immersed in the solution 

 was covered with a solid but thin coat of copper, which 

 viewed in front had the colour of pure copper, but dull and 

 without brightness ; but viewed obliquely had a velvety ap- 

 pearance, and a paler colour. Seen through a lens this 

 crust appeared crystalline, and of a metallic brightness. 

 The slightest rubbing gave it the polish of the purest cop- 

 per. Between the part covered with this copperj' incrusta- 

 tion and the oxided part there was a stripe a third of a line 

 broad, where the slip of copper remained unaffected ; and 

 above this, for the space of two inches, the copper wa» 

 covered with black brown oxide. 



VL 



