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 not 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 MgS0 4 , then try it on salts of Fe, Mn, 

 Co, Ni, Al, Zn and Cd. Repeat the experiments, this time adding the HNa 2 P04 

 before the NH 4 OH. 



b. 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 1 and II. 



ZINC. 



Crystal Forms and Optical Properties of Common Salts 

 of Zinc. 



A. ISOTROPIC. 



B. ANISOTROPIC. 



Hexagonal. 



Tetragonal. 



Ortlwrhombic . — Chromate; sulphate. 1 



Monoclinic. — Acetate; potassium-zinc sulphate. 



Triclinic. 



DETECTION. 



A . By Means of Potassium Mercuric Thiocyanate. 

 Apply the reagent by Method /, 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. 



