MICROCHEMICAL REACTIONS OF ZINC 353 
nium hydroxide, for it should be remembered that there must 
be not only enough ammonium present to unite to form the 
proper compound, but that this latter salt will ndt separate save 
in alkaline solution. 
It must also be borne in mind that the use of too strong 
ammonium hydroxide in excess so reduces the solubility of 
many salts as to cause their separation. Hence it is necessary 
to avoid, in reactions of this character, deciding too hastily as 
to the result of a test. 
EXPERIMENTS. 
a. Try modification I on a solution of MgS04, then try it on salts of Fe, Mn, 
Co, Ni, Al, Zn and Cd. Repeat the experiments, this time adding the HNa2P04 
before the NH4OH. 
h. Try modification II upon the same salts and combinations used in a. 
c. Make mixtures, trying various combinations of the above with members of 
Groups I and II. 
ZINC. 
Crystal Forms and Optical Properties of Common Salts 
of Zinc. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. 
Tetragonal. 
Orthorhombic. — Chromate; sulphate.^ 
Monoclinic. — Acetate; potassium-zinc sulphate. 
T riclinic. 
DETECTION. 
A. By Means of Potassium Mercuric Thiocyanate. 
Apply the reagent by Method I, page 299. 
This reagent furnishes us with one of the best and the most 
generally useful methods for detecting the presence of zinc, 
copper, cadmium and cobalt, and will also furnish evidence of 
the presence of iron, silver, lead and gold. 
For the qualitative examination of simple salts and alloys it 
1 If formed in the presence of ferrous sulphate, monoclinic. 
