188 Chemical Notices : — M. Stas on the 



Silver was prepared partly by the reduction of chloride of 

 silver by milk-sugar, and potash, but more advantageously by 

 precipitation with sulphite of ammonia. For this purpose silver 

 coin was dissolved in nitric acid and the solution evaporated to 

 dryness, the residue fused in order to decompose any admixture of 

 platinum salts, then dissolved inammoniacal water, and mixed with 

 the requisite quantity of sulphite of ammonia. The reduction 

 takes place slowly in the cold, more rapidly when heated to 

 60-76°. The solution of silver must be so dilute that it does 

 not contain more than 2 per cent, of silver. The precipitated 

 silver is washed with ammoniacal water, and then concentrated 

 ammonia poured upon it. On standing in the air the liquid ought 

 not to become blue; if it does, some silver is dissolved. As much 

 as five pounds of silver were worked up at once. In order to 

 test the purity of the silver, it was heated on a lime support in 

 the oxyhydrogen blowpipe. It fused without being covered with 

 any spots, began to boil with evolution of a bright blue vapour 

 (a greenish vapour indicates the presence of copper), and finally 

 distilled without leaving a residue. Distillation is probably the 

 best means of obtaining perfectly pure silver. 



Large burettes were used for estimating the silver solution, 

 and were kept in a reservoir of water always at the same tempe- 

 rature. The normal solutions were placed in a perfectly dark- 

 ened room, which was lighted by a gas-lamp with a yellow screen. 

 Determinations of silver by diffused daylight, according to the 

 author, never gave perfectly accurate results. The estimation 

 was effected in a black box provided with a slide, lighted by 

 a lamp whose light passed first through a round flask filled with 

 a solution of neutral chromate of potash. Only a thin column 

 of the solution to be tested was thus lighted. But by this ar- 

 rangement it was possible to detect ^ of a milligramme of 

 silver in a litre of solution, and, by waiting a suitable time (fifteen 

 minutes, for instance), as little as J 10 ^ of a milligramme. 

 Ten grms. of the pure silver were dissolved at a time and mixed 

 with normal solution of chloride of sodium (containing 5*42 

 grms.), and the excess of the silver dissolved determined by 

 means of the normal solution of chloride of sodium. The percen- 

 tage of pure silver was found = 99*994-1 0000 per cent., mean 

 99-997. 



The Sal-ammoniac was purified in different ways. (1) Hot sa- 

 turated boiling solution of sal-ammoniac was boiled with nitric 

 acid of 1*4 spec. grav. as long as chlorine was given off. Hy- 

 drate of lime was then added, and the disengaged ammonia col- 

 lected in water and saturated with hydrochloric acid gas. The 

 sal-ammoniac thus obtained was dried at 100° in a current of 

 ammoniacal gas, and then sublimed at as low a temperature as 



