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- 
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