354 ELEMENTARY CHEMICAL MICROSCOPY 



filtration should then be resorted to and the clear solution care- 

 fully concentrated to remove the excess of acid until a drop of 

 water causes a precipitate of antimonyl (or bismuthyl) chloride. 

 Then very carefully add hydrochloric acid with thorough stirring, 

 until the precipitate just dissolves. 



EXPERIMENTS. 



Defer until Bi is being studied. 



ANTIMONATES. 



The composition of the various antimonates commercially 

 available appears to be quite uncertain. The only one of im- 

 portance is the potassium salt sold variously as potassium anti- 

 monate, metantimonate or pyroantimonate ; it usually conforms 

 fairly closely to the formula H 2 K 2 Sb 2 O7 6 H 2 0. It is difficultly 

 soluble even in boiling water. 



Sodium salts in neutral solution yield, with antimonates of this 

 type, very insoluble sodium pyroantimonate, separating as tiny 

 lenticular grains or larger fusiform crystals singly or uniting in 

 more or less globular masses. From dilute solutions what appear 

 to be tetrahedra, octahedra or rectangular prisms are formed. 

 Although appearing to be isometric the crystals are to be referred 

 to the tetragonal system. 



Magnesium salts in neutral solution yield H 2 MgSb 2 07 9 H 2 O 

 first as an amorphous precipitate, later crystallizing in thin 

 transparent colorless hexagonal plates, and as small, irregular 

 spherulites. Occasionally stars or rosettes or short hexagonal 

 prisms are obtained. The magnesium salt is dimorphic, being 

 either hexagonal or monoclinic according to conditions. 



Of the two tests that with sodium is the more satisfactory. 



If it is necessary to neutralize a test drop in testing for anti- 

 monates use potassium carbonate. 



Ammonium salts interfere with the sodium and magnesium 

 tests. 



BISMUTH. 



Crystal Forms and Optical Properties of Common Salts 



of Bismuth. 

 A. ISOTROPIC. 



