PRECIPITATION OF OXIDES BY THEIR OWN METALS. ^^f 



f>ottoiii of the slip. The experiment terminated in much 

 less time. 



5. To vary the third experiment, I made a solution of Nitrate of ««p- 



copper in nitric acid, so as to leave some metallic copper in P^*^ *'*^^ ^^'*" 



1 , , . , , „ J , . ' 4 1 tie excess *f 



the saturated solution ; and then lormed a chain. At the meul. 



expiration of a few minutes the usual phenomena presented 

 themselves, except that at the point of contact of the two 

 liquors a slight turbidness appeared, occasioned by the pre- 

 cipitation of the nitrate of copper at a minimum in the 

 form of small flocks of a greenish white. At the com- 

 mencement some flocks were deposited on the edges of the 

 slip of copper, but they afterward disappeared. As, when 

 water had been added, the liquor was rendered absolutely 

 turbid by the separation of the oxide of copper, which was 

 present in excess, 1 took out the slip of copper, and was 

 agreeably surprised by an unexpected result: as far as the 

 slip had been immersed in the cupreous solution, it was 

 covered with another slip of copper extremely thin, on 

 which were several little knobs of the size and shape of 

 pin's heads, which looked metallic, smooth, and as if they 

 had been melted, and viewed with a lens had one or two lit- 

 tle openings on the side. It appeared to me loo, that the 

 flocks observed on the edges of the slip had been converted 

 into similar little knobs, for the edges were covered witli 

 them in different places. Whence could ariise this interest- 

 ing phenomenon of the separation of the copper in the form 

 of little globules ? 



6. This experiment was again vxiried by allowing the so- Kiir.ite of eo j- 

 lution of copper to contain a slight excess of acid. The I""'' v- ''h ex- 

 result was the same as in experiment 3, except that the » <* ' 

 copper was longer in being precipitated ; this not taking 



place till the excess of acid appeared to be deadened, 

 which was effected with the extrication of a great many 

 bubbles of gas ; and the separation took place only at the 

 bottom of the slip, and in the form of little grains. 



Many other experiments, infinitely vuried in order to ob~ t^eJuction nf 

 tain more extensive cupreous vegetations, taught me, that copper most 



^, J .. r. -1 p coniplole witli 



the reduction or copper by means of copper warn more com- a s/nmated <i; 



plete in proportion as the soluti<9n was more concentrated, i^'i'e^^l. n.u- 



i • ^ /• ^. A J ii T r> tr..l soiti'.ior, 



the point of saturation more exact, and the shp ot copper ' 



broad, 



