Royal Society, 139 



results must be influenced by the smaller quantity gathered in our 

 horizontal gauges in proportion to the differences. We hope Mr. 

 Symons will give especial attention to this subject. We hear 

 much now-a-days of the need for Government aid to science ; and yet 

 our Government establishments have not detected these anomalies ! 



XIX. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 75.] 



April 11, 1872.— The Earl of Rosse, D.C.L., Vice-President, in the 



Chair. 

 ''pHE following communication was read : — 

 -■- "The Action of Oxygen on Copper Nitrate in a state of Ten- 

 sion." By J. H. Gladstone, Ph.D., F.R.S., and Alfred Tribe, F.C.S. 



In our experiments on the action between copper and nitrate of 

 silver in solution, we frequently noticed that the tips of the silver 

 crystals became red, as though coated with a thin layer of metallic 

 copper. 



This apparent deposition of a positive on a more negative metal of 

 course raised our curiosity, and led us to look closely into the 

 circumstances under which it occurred. We found that it took 

 place only when the nitrate of silver was exhausted, and only on 

 those silver crystals which remained in metallic connexion with the 

 copper. We found, too, that the cupreous coating formed most 

 readily where air had the freest access, and, in fact, that it would 

 not form at all in vessels from which oxygen was excluded, nor 

 on those white crystals w'hich were far below the surface of the 

 liquid, though they might be in immediate contact with the copper 

 plate. When an inverted jar was filled with nitrate-of-copper solu- 

 tion and silver crystals resting on branches of copper, and the liquid 

 was displaced by oxygen gas, it was found that the tips of the crystals 

 became red, and the solution gradually filled the jar again by the ab- 

 sorption of the gas. In the same way the oxygen was absorbed from 

 air, or from its mixtures with hydrogen or carbonic anhydride. 



This action was further studied by employing plates of the two 

 metals instead of copper covered with silver crystals. When the two 

 plates, connected by a wire, were partially immersed in an ordinary- 

 aqueous solution of copper nitrate, it was found that a slight yel- 

 lowish deposit made its appearance speedily all over the silver plate, 

 and went on increasing for a day or two, while at the air-line there 

 was a thicker deposit, which gradually grew and extended itself a 

 little below the surface. This deposit changed from yellowish to red, 

 and under the microscope presented a distinctly crystalline appear- 

 ance. 



Thinking that this slight crust all over the silver plate was due 

 to air dissolved in the solution itself, we took advantage of the re- 



