MICROCHEMICAL REACTIONS OF SILVER 
377 
B. ANISOTROPIC. 
Hexagonal. — Iodide;^ secondary arsenate; sec¬ 
ondary phosphate. 
Tetragonal. 
Orthorhombic. — Chromate; nitrate; nitrite; sul¬ 
phate; potassium-silver iodide. 
Monoclinic. 
Triclinic. — Bichromate. 
DETECTION. 
A. By Means of Hydrochloric Acid. 
Apply the reagent by Method 77 /A, page 302, to the test 
drop previously acidulated with nitric acid. 
If silver is present an immediate precipitate should result. 
Examine under the microscope. Silver chloride is so insoluble 
in water that it is thrown down as an amorphous mass. If the 
precipitate is wholly crystalline, either silver is absent or else 
present in very small amount. In order to identify silver in an 
amorphous precipitate it is necessary to recrystallize it. Before 
so doing it is always advisable, and often necessary, to first 
remove the solution from the precipitate and wash the latter. If 
the hydrochloric acid has been carefully added and the drop not 
stirred, it is easy to draw off the clear solution from the curdy, 
heavy precipitate of silver chloride. When the amount of pre¬ 
cipitate is very small it is best to have recourse to the centrifuge 
to accomplish the separation. After removing the supernatant 
liquid, wash the precipitate once or twice with hot water acidified 
with nitric acid. The washed precipitate is then recrystallized 
from concentrated hydrochloric acid, or from ammonium hy¬ 
droxide. 
To the precipitate of silver chloride, at the corner of a slide, 
add a drop or two of concentrated hydrochloric acid, and heat 
the preparation over the micro-flame. If the precipitate is not 
completely dissolved, rapidly draw off the hot acid, without 
exercising any great care. On cooling, tiny crystals of silver 
chloride separate. Octahedral crystals predominate. 
1 Upon heating, Agl becomes isometric. 
