362 
ELEMENTARY CHEMICAL MICROSCOPY 
bristling masses and tiny crosses and stars, closely resembling 
the forms obtained with cadmium. They differ, however, from 
the cadmium salt in that they do not polarize. 
Nickel gives a light green amorphous precipitate; cobalt a 
similar pink one; while iron, if heated, yields a yellow deposit. 
Mercurous salts (nitrate) give a gelatinous amorphous mass 
of a yellowish tint. 
Mercuric salts and those of silver, lead, tin, antimony, bismuth, 
aluminum, magnesium and the alkaline earths appear to give 
no precipitates and to yield no crystals even in concentrated 
solution or upon evaporation. 
Precautions. 
The solution should be neutral or but faintly acid and should 
be moderately concentrated with respect to zinc. 
If no result is obtained upon the first test, make a second, 
employing a considerably greater amount of the unknown 
substance. 
Heating the preparation hastens the reaction. 
If a precipitate is obtained, zinc, cadmium, copper, nickel, 
cobalt, iron or manganese are present and, conversely, if no pre¬ 
cipitate appears, these elements must be absent. 
Sodium nitroprusside is thus a convenient group reagent. 
EXPERIMENTS. 
a. Try the reagent upon several different concentrations of Zn. 
b. Try with Cd, then with mixtures of Zn and Cd. 
c. Try salts of Cu, Ni, Co, Mn, first as pure salts, then as mixtures with Zn. 
CADMIUM. 
Crystal Forms and Optical Properties of Common Salts 
of Cadmium. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. — Iodide, ammonium-cadmium bro¬ 
mide; ammonium-cadmium chloride; potas¬ 
sium-cadmium chloride. 
