364 
ELEMENTARY CHEMICAL MICROSCOPY 
Precautions. 
Cadmium salts of the organic acids, as, for example, cadmium 
acetate, fail to yield a satisfactory rest. It is therefore best to 
evaporate the unknown with nitric acid and drive off the excess 
of acid before adding the thiocyanate reagent. It follows that 
the addition of sodium or ammonium acetate to very acid solu¬ 
tions to lessen the effect of the mineral acid is in this case unwise. 
It is better to evaporate to dryness. 
B. By Means of Oxalic Acid. 
Read Method C, Zinc, page 359. 
The typical crystals of cadmium oxalate CdC204 • 3 H2O con¬ 
sist of long, clear, colorless, monoclinic prisms, singly, in X’s, 
or in clusters. The.obliquely truncated ends constitute a dis¬ 
tinctive feature. 
Manganous oxalate MnC204 • 3 H2O separates in groups of 
radiating prisms, which the careless observer sometimes con¬ 
fuses with the cadmium salt or vice versa. The ends of the 
prisms of the two salts are quite different however in appearance. 
C. By Means of Sodium Nitroprusside. 
See Zinc, Method D, page 361. 
MERCURY. 
Crystal Forms and Optical Properties of Common Salts 
of Mercury. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. 
Tetragonal. — Mercurous bromide, chloride and 
iodide; mercuric cyanide; red mercuric 
iodide. 
Orthorhombic. — Mercuric bromide; mercuric chlo¬ 
ride; yellow mercuric iodide. 
