350 
ELEMENTARY CHEMICAL MICROSCOPY 
Elements of the magnesium group interfere. Lithium like¬ 
wise interferes. But the chlorides of iron and aluminum and 
the salts of boric acid have no appreciable effect on the reaction. 
When in doubt as to the nature of a precipitate formed by the 
treatment with HNaCOs, decant the supernatant solution, which 
is easily done since the crystals of calcium carbonate adhere to 
the glass slide, wash the residue, and then add dilute sulphuric 
acid. If the precipitate is due to calcium, characteristic crys¬ 
tals of CaS04 • 2 H2O appear. 
Primary sodium carbonate is of more value as a group reagent 
than as an identification test. Moreover, chance formations of 
crystals of alkali carbonates may be met with in the progress 
of the systematic analysis of unknown material, particularly 
when testing for zinc (q.v.). 
MAGNESIUM. 
Crystal Forms and Optical Properties of Common Salts 
of Magnesium. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. — Pyroantimonate. 
Tetragonal. — Fluoride. 
Orthorhombic. —Ammonium-magnesium phosphate; 
sulphate; primary tartrate. 
Monoclinic. —^ Acetate; chloride; nitrate; primary 
phosphate; ammonium-magnesium sul¬ 
phate; potassium-magnesium sulphate; 
normal tartrate. 
Triclinic. 
DETECTION. 
A. By Means of Uranyl Acetate and Sodium Acetate. 
This test has already been described at length under 
Sodium, Method A, page 321. 
B. By Means of Secondary Sodium Phosphate {HNa^POf) 
in Ammoniacal Solution. 
For the reaction see Ammonium, page 332. 
