MICROCHEMISTRY. 151 



metallic lead added to a solution of silver salts causes 

 the separation of metallic silver in the form of dendritic 

 skeleton crystals. 



The other elements are identified by similar specific 

 reactions. Copper is at once indicated by the color of 

 the reduced metal and the solution. Bismuth is detected 

 by the large hexagonal plates of bismuth sulphate formed 

 by warming with sulphuric acid and again cooling. 

 Tin solutions, with an acid reaction, on the addition of 

 sodium iodide, produce characteristic crystals of sodium 

 iodostannites and iodostannates. Cadmium forms a white 

 precipitate with ammonium hydrate. 



7. The Determination of the Acid Radicles. — In 

 studying the acid radicles in an unknown solution, it 

 is first necessary to determine the presence or absence of 

 organic acids. This may be accomplished by mixing a 

 drop with a minute drop of a saturated solution of potas- 

 sium permanganate and adding concentrated sulphuric 

 acid. In the presence of organic acids, nitrites, sul- 

 phites, and hyposulphites, the pink solution is decolorized. 

 The last three classes of compounds produce decoloriza- 

 tion when acetic acid is substituted for sulphuric acid, 

 while the organic bodies do not. 



If organic acids be absent, a drop of the solution is 

 tested for volatilization with acetic acid and sulphuric 

 acid successively. A drop of silver nitrate placed on . 

 the under side of the upper watch-glass serves to absorb 

 the vapors and record their presence by precipitation. 

 The first group of acids decomposed by acetic acid in-- 

 cludes the nitrites, cyanides, carbonates, sulphites, hypo- 

 sulphites, sulphides, and hypochlorites. The second 



