44i PRECIl'ITATION OF OXIDES BY TIIEIR OWN METALS, 



and accelerated broad, thick, and polished; and that when a little nitric 

 acidul^iiug the '^^^^ ^^^'^ added to the water the result of the operation was 

 water. accelerated by the oxidation of the metal being effected 



more copiously in the superior fluid : but that a too great 

 excess of acid was unfavourable to its success, the process 

 going on with too much commotion, and producing too 

 epeedy a mixture of the liquors, as well as too great a spe- 

 cific gravity of the upper, which destroys the action of the 

 chain. 



Experiments with the solution of nitrate of silver, ivater, and 

 silver. 



Exp. with ni- 7- Into a small narrow glass I put a solution of two 

 tcaie ot silver. (J,.jichrns of nitrate of silver in half an ounce of water, and 

 poured on it six drachms of distilled water, acidulated with 

 half a drachm of pure nitric acid. The chain was com- 

 pleted by a little piece of solid silver, narrow and ending 

 in a point, which was fixed in a bit of coik. The action 

 was almost instantaneous. A point of was formed, and 

 marked by a very bright transverse line, that remained in- 

 tact. Immediately below this point metallic silver separated 

 in shining grains resting one against another in a horizontal 

 line, which continued to be deposited the whole length of 

 the slip, which was half an inch. These grains increased 

 for twelve hours below the point of 0. The slip of silver 

 became gray, and was gradually covered with black oxide. 

 At the expiration of this time the action of the silver was 

 no longer perceptible, and the slightest touch occa^^ioned it 

 to drop asunder, as it was corroded where the acid li(|uor 

 was in contact with the air. During the whole process there 

 were but few bubbles extricated in the upper liquor. The 

 «lip of silver covered with little shining knobs exhibited a 

 pleasing sight, when viewed either with a lens or the uaked 

 eye. Professor Bernhardi examined them with a micro- 

 scope, which magnified 200000 times, and then dis- 

 tinctly perceived, that they were cubes truncated at the 

 edges. 

 The same with 8. I repeated the preceding experiment with a view to ef- 

 lity^'^^"^ *^"^"' ^^^^ ^ mort considerable separation of silver. Accosdingly 



I dis- 



