320 ELEMENTARY CHEMICAL MICROSCOPY 



B. ANISOTROPIC. 



Hexagonal. — Nitrate (pseudo O) ; normal phos- 

 phate; potassium-sodium molybdate; silico- 

 fluoride. 1 



Tetragonal. 



Orthorhombic. — Iodate; nitrite; potassium-sodium 

 tartrate; normal tartrate; primary phos- 

 phate. 



Monoclinic. — Acetate; secondary arsenate; borates, 

 tetra and meta; carbonate; primary carbon- 

 ate ; chromate ; f errocyanide ; 2 oxalate, ferric- 

 sodium; secondary phosphate; ammonium- 

 sodium acid phosphate; sulphate; primary 

 sulphate; thiosulphate; zinc-sodium sul- 

 phate. 



Triclinic. — Bichromate; bitartrate; primary oxa- 

 late. 



DETECTION. 



A. — By means of Uranyl Acetate. 

 Apply test by Method IV, page 303. 



Sodium yields with uranyl acetate small faintly yellow tetra- 

 hedra, appearing black by transmitted light. The compound 

 formed probably has the formula NaC 2 H 3 02 • UC^^HaC^- 

 The crystals are isotropic belonging to the isometric system. 



Potassium, rubidium, cesium and ammonium yield long 

 needles or slender prisms of the tetragonal system of greater 

 solubility than the sodium compound and therefore not appear- 

 ing until the preparation has evaporated almost to complete 

 dryness. 



Because of the high solubility of ammonium uranyl acetate, 

 Schoorl 3 has suggested its use for detecting sodium instead of 

 simple uranyl acetate. The test thus made is more sensitive, 

 but lacks the convenience of the method given above in that no 



1 Na 2 SiF6 is said to be pseudohexagonal. 



2 Na 4 Fe(CN)6 • 12 H 2 is pseudotetragonal. 



3 Lenz u. Schoorl, Zeit. anal. Chem., 50 (191 1), 263. 



