MICROCHEMICAL REACTIONS OF POTASSIUM 
327 
d. Add a little CaCU to a solution containing Na and test as above. 
e. To a solution of NaCl add a little SiOz or a trace of sodium silicate, then 
add NH4F 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); silicofluor- 
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 I, page 299. 
In a few moments, relatively large and beautifully formed, 
strongly refractive, bright, deep yellow crystals of K2PtCl6 
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. 
