42 PRECIPITATION OF OXIDES BY THEIP. OWN METALS. 



Kxp.fwith ni- 3. Half an ounce of copper was dissolved in nitric acid, 

 (.0 ^^P\'^^' loiiin^ care that there should be no greater excess of acid 

 than vras absolutely necessary for the solution of the salt. 

 The solution being evaporated to two ounces, the chain was 

 formed by adding three ounces of distilled water above it, 

 nnd immersing in the two fluids the slip of polished cop- 

 per, taking care to keep it a few lines from the bottom of 

 tlie glass by fastening it to a bit of cork. The two fluids 

 appeared at first quite separate from each other : but a few 

 minutes after the chain was formed, a narrow but very 

 bright transrerse line appeared on the copper at the point 

 of their separation ; above this point the capper was much 

 darker; and at the end immersed in the fluid, small and 

 almost imperceptible filaments were deposited, which gra- 

 dually increased, but ultimately disappeared. The bright 

 line increased greatly, and the part that was in the water 

 grew darker, till it became a brown black. At the end of 

 72 hours, when the two liquids appeared to be completely 

 mixed, and the activity of the chain destroyed, I took out 

 the slip of copper, and found it in the following state. 

 Near the centre there was a bright place about a quarter 

 of an inch broad, where neither oxidation nor precipitation 

 of the copper was perceivable. Above this line was a slight 

 coat of brown black oxide of copper; and below a red pul- 

 verulent stratum of copper, which gradually thickened to- 

 ward the end of the slip, and assumed a striated appear- 

 ance. This stratum, viewed with a lens, appeared to be 

 formed of a collection of little grains, which acquired a 

 metallic lustre on being rubbed. The result of this expe- 

 riment showed evidently, that, under suitable circum- 

 stances, a very active electro-galvanic chain might be formed 

 in this manner, by means of which copper might be pre- 

 cipitated in the metallic state by means of copper itself. 

 Nitvnte of cop. 4. To learn what would be the reductive power of such 

 lier and water ^ chain, if the water employed were acidulated with -r'-- of 

 nitric acid. nitric acid, I proceeded nearly as in the foregoing experi- 

 ment. The result was much the same, only the slip of 

 copper was more speedily oxided in the acid liquor, some 

 bubbles of gas escaped, and the copper was deposited in a 

 thicker stratuuij and with a lustre almost metallic, at the 



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