MICROCHEMICAL REACTIONS OF POTASSIUM 327 



d. Add a little CaCl2 to a solution containing Na and test as above. 



e. To a solution of NaCl add a little Si0 2 or a trace of sodium silicate, then 

 add NH 4 F and an acid. 



/. Repeat using some Ti compound in place of that of Si. 

 g. Test a salt of Ba as above, then a mixture of Ba and Na. Note that it 

 constitutes an excellent test for Ba even in the presence of Na. 



POTASSIUM. 



Crystal Forms and Optical Properties of Common Salts 

 of Potassium. 



A. ISOTROPIC. 



The alums (I); chloride (I); bromide (I); iodide 

 (I); cyanide (I); molybdate (I); siliconuor- 

 ide (I or H). 



B. ANISOTROPIC. 



Hexagonal. — Barium-potassium ferrocyanide; bo- 

 rate, tetra; silicofluoride (H or I). 



Tetragonal. — Arsenate ; cyanate ; secondary phos- 

 phate. 



Orthorhombic. — Antimonyl tartrate; chromate; ni- 

 trate; perchlorate; permanganate; sulphate; 

 primary sulphate; thiocyanate; primary 

 tartrate; sodium-potassium tartrate. 



Monoclinic. — Carbonate; chlorate; ferricyanide; 

 ferrocyanide; iodate; oxalates; normal tar- 

 trate. 



Triclinic. — Bichromate; persulphate. 



DETECTION. 



A. By Means of Chloroplatinic Acid. 



Apply the reagent by Method /, page 299. 

 In a few moments, relatively large and beautifully formed, 

 strongly refractive, bright, deep yellow crystals of K 2 PtCl6 

 appear. The usual form is that of the regular octahedron, some- 

 times showing faces of the cube. Horizontally elongated octa- 

 hedra, or octahedra shortened parallel to one of the pairs of 

 faces, are not unusual. 



