PRECIPITATION OF OXIDES BY THEIR OWN METALS. 4^5 



I dissolved an ounce of fine silver in pure nitric acid, and 

 added water so as to form a saturated solution weighing six 

 ounces. This solution I poured into a cylindrical vessel, 

 and very cautiously added eight ounces of water. I then 

 completed the chain with a pointed slip of silver six inches 

 long-, and one inch broad. The action was not perceptible 

 till after three or four hours, when a point of was observ- 

 able, above which the tnetal became gray, while below sin- 

 gle grains of silver w'ere deposited, so small as to be scarcely 

 distinguishable by the eye. In 7^2 hours these points had 

 acquired the size of pin's heads in seven or eight places. 

 The upper part of the slip was turned of a deeper gray, but 

 tlie two liquors being perfectly mixed, there were no hopes 

 of obtaining a more complete result. 



This expetiiment affords fresh proof, that the activity of Activity in 



a chain bears a certain ratio to that of the oxidation. proportion to 



the oxidation. 



Q. The liquors of the preceding experiment were evapo- Nitrate of sii- 



rated to six ounces, and after being returned into the same '^^^ ^"^ water 

 . • 1 1 ^ j/ VI r. acidulatedwitb 



vessel, live ounces or water acidulated with one ot pure ninic acid. 



nitric acid of the specific gravity of l"25 were added with a 

 great deal of caution. The chain was completed with the 

 slip of silver that has been mentioned. The action 'began 

 immediately. A point of was apparent a quarter of an 

 inch broad, where the slip of silver remained unaffected. 

 Above this point was formed black oxide ; and beneath, 

 throughout the whole breadth "of the slip, a line of knobs 

 of shining silver, exactly as in experiment 7, but in a 

 somewhat larger proportion. These little grains increased 

 for 36 hours, as well as the black oxide. The silver sepa- 

 rated had the same form as in experiment 7, except that 

 some agglutinations of silver at the point of the slip were 

 dull, though they became shining on being pressed upon 

 with a hard substance. On taking out the slip at the ex- 

 piration of 36 hours, it divided into two parts. It was par- 

 ticularly corroded where it had been in contact with the 

 liquid at the upper part, at which place it was completely 

 converted into black oxide. 



Mxperimentg 



