332 ELEMENTARY CHEMICAL MICROSCOPY 



A. ISOTROPIC. 



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

 (I); siliconuoride (I). 



B. ANISOTROPIC. 



Hexagonal. — Fluoride. 



Tetragonal. — Borate (NH^I^Oy • 4 H 2 0; primary 

 phosphate. 



OrthorJiombic. — Bicarbonate; nitrate; 1 primary 

 oxalate; normal oxalate; perchlorate; pri- 

 mary tartrate; sulphate. 



Monoclinic. — Secondary arsenate; bichromate; 

 chromate; molybdate; persulphate; ammo- 

 nium-sodium acid-phosphate; secondary 

 phosphate; primary sulphate; ammonium- 

 ferrous sulphate; thiocyanate; normal 

 tartrate; thiosulphate. 



Triclinic. 



DETECTION. 



Unless the analyst is dealing with a simple salt of ammonium, 

 it is always best to expel the NH 3 from the compound by distilla- 

 tion (see page 292) with sodium hydroxide or magnesium oxide. 

 The ammonia set free is fixed by absorption in a drop of dilute 

 hydrochloric acid (or other acid). The resulting solution of 

 ammonium chloride is concentrated or evaporated to dryness 

 and the material thus obtained tested for ammonium. 



A. By Means of Chloroplatinic Acid. 



See Method 7, page 299, and discussion and precautions 

 given under Potassium, test A, page 327. 



B. Through the Formation of Ammonium Magnesium Phos- 

 phate. 



The typical reaction for this identity test may be written 



NH4CI + MgCl 2 + HNa 2 P0 4 -I- NaOH = 

 NH 4 MgP0 4 + 3 NaCl + H 2 0. 



1 NH4NO3 is pseudotetragonal. 



