48 ■ PROCEEDINGS OF THE AMERICAN ACADEMY 



ammonio-argentic nitrate, prepared in the first case from metallic silver, 

 and in the last case from crystallized nitrate of silver, with the least 

 possibie excess of ammonia. During the process, a current of COg 

 vs^as passed through the solution, which was boiled with the precipitate 

 until all odor of ammonia had disappeared, when violent bumping en- 

 sued. After having been collected and dried, the sulphide was heated, 

 in the first case to 280*^, and in the last case to 300°, in a current of 

 COj. We observed no sublimate, and there was no loss of w^eight with 

 either preparation. Of the preparation d, seven grammes were boiled 

 with strong hydrochloric acid until completely converted into chloride, 

 which was then tested for sulphur, but none could be detected. The 

 products of the decomposition of several of the j^reparations were tested 

 for ammonia, and other volatile bases which might possibly have been 

 occluded by the precipitated sulphide. Ammonia was at first found in 

 abundance, but this was soon traced to an impurity in the hydrogen 

 used in the reduction ; and after this source of error was removed not 

 the smallest quantity of any such product could be detected. It will 

 thus be seen that these very closely according results were obtained 

 with seven different preparations, made in part by different processes ; 

 and, further, that we had the strongest evidence of the purity of the 

 material used ; and, lastly, that the perfect metathesis of the sulphide 

 with hydrochloric acid, leaving no residue of either elementary sub- 

 stances, proved that the silver was united to the sulphur in atomic 

 proportions. Nevertheless, all these determinations were in error, and 

 the error arose in this way : — 



The argentic sulphide, held by a porcelain nacelle in a jDorcelain 

 tube heated by a gas furnace, was reduced in a current of hydrogen 

 gas. The hydrogen was prepared in an automatic generator, from 

 clippings of sheet zinc, common sulphuric acid, and w'ater, in the 

 usual way ; but, before reaching the porcelain tube, passed through a 

 very long series of purifiers and driers, containing iu order quick lime, 

 soda lye, solution of acetate of lead, solution of argentic nitrate, sul- 

 phuric acid, and chloride of calcium. The object we had chiefly in 

 view was to remove from the gas any traces of arseniuretted hydrogen 

 or similar compounds ; and we felt assured of its purity in this respect, 

 on finding that it formed no metallic mirror even after passing for 

 several hours through a glass tube heated to redness, and caused 

 no darkening of "lead paper" after very prolonged exposure. The 

 reduction of the sulphide of silver was of course attended with the 

 evolution of hydric sulphide, and the process was continued until no 

 trace of this substance could be detected with " lead paper " in the gas 



