Page:Experimental researches in chemistry and.djvu/29

14 loss being supposed to be water, some of which had condensed in the neck of the retort. Now—

The same method of analysis was applied to oxide of silver, precipitated by potash from nitrate of silver, it having been well washed and dried: 40 grains gave 7&middot;9 cubical inches, and 36&middot;4 grains of silver remained. The 7&middot;9 cubical inches = 2&middot;686 grains, and

the number for silver very nearly as given in the most correct elementary treatises on chemistry. There appears, therefore, to be no error in the mode of analysis, and the oxide by ammonia seems to contain less oxygen than that precipitated by alkalies. Again,—

30 grains of the oxide of silver were put into a retort, and decomposed with every precaution as before; the silver left weighed 27&middot;4 grains, and the quantity of gas given off was 4&middot;125 cubical inches. I suspected that a small portion of carbonate of silver had been mixed with the oxide, for when the ammoniacal solution has been long exposed to the air, much carbonate of ammonia and of silver is formed in it; the gases were therefore placed over solution of potash, and were reduced in bulk to 3&middot;625, which was pure oxygen. This volume is equivalent to 1&middot;2325 gr., and 1&middot;2325&#8758;27&middot;4 &#8759; 7&middot;5&#8758;166&middot;7, a proportion of silver still higher than in the first experiment, but which may be accounted for by the purification of gas and the small quantity of oxygen that remained in the retort.

In a third experiment, 24 grains of silver were left; 4&middot;25 cubical inches of gas were given off, which decreased over potash to 4. In order to estimate the proportion of azote arising from the air in the retort, the 4 were treated with nitrous gas of known purity, and gave results equal to 3&middot;475 of pure oxygen. This is equal to 1&middot;1815 gr., and 1&middot;1815&#8758;24 &#8759; 7&middot;5&#8758;152&middot;3.

One or two other experiments varied considerably from this, giving a greater proportion of silver, but the mean of many gave the oxygen to the silver as 7&middot;5 to 157&middot;4.