376 ELEMENTARY CHEMICAL MICROSCOPY 



jet black by transmitted light, grayish by reflection, their growth 

 is rapid and vigorous, finally occupying the entire area of the 

 drop, and is characteristic of bismuth. Antimony yields black 

 mossy dendrites but rarely feathery or curving; they appear 

 more granular in structure. 



Copper separates as black, compact stout mossy masses with 

 somewhat tabular or angular ends. 



Cobalt resembles copper somewhat but forms dendrites less 

 readily. Nickel can be made to yield a crystalline deposit only 

 with great difficulty; only small mossy patches are usually 

 obtainable. 



Gold yields very compact mossy or granular dendrites and 

 irregular botryoidal black masses which soon exhibit the char- 

 acteristic golden yellow reflections of the metal. 



Precautions. 



To obtain the best results, the solutions should be practically 

 neutral or only very slightly acid, otherwise the rapid evolution 

 of hydrogen will cause the disintegration of the deposited crystal 

 masses. If free mineral acid is present add sodium acetate. 



Use only cold solutions. 



Employ only a very minute fragment of zinc, otherwise the 

 area of metal upon which deposition can take place is so great 

 that really characteristic growths will not be obtained. 



In general a moderate concentration is essential to the forma- 

 tion of satisfactory dendrites. 



EXPERIMENTS. 



If a number of elements have not already been tested under Method 77/, page 

 300, try a fragment of Zn in drops of solutions of salts of Pb, Bi, Sb, Sn, Cu, Cd, 

 Pt, Au and Hg. 



SILVER. 



Crystal Forms and Optical Properties of Common Salts oj 

 Silver. 



A. ISOTROPIC. — Chloride (I); bromide (I); iodide 

 (I or H). 



