MICROCHEMICAL REACTIONS OF AMMONIUM 
333 
To the drop to be tested add a fragment of sodium phosphate 
and a very little magnesium chloride, stir thoroughly. Beside the 
drop place a drop of dilute solution of sodium hydroxide and 
cause this drop to flow into the other. 
Ammonium magnesium phosphate separates in crystals having 
the formula NH4MgP04 • 6 H2O, belonging to the orthorhombic 
system and exhibiting an exceptionally strong tendency to assume 
hemihedral, hemimorphic and skeletal forms. This compound 
usually separates first as an almost amorphous precipitate which 
soon changes into star-like and X-shaped crystallites. Soon the 
X’s fill out and envelope-like crystals result and at the same time 
rectangular prisms resembling roofs of houses appear. 
In preparations containing but little of the ammonium mag¬ 
nesium phosphate the stars and X’s are usually absent. 
Precautions. 
Since the amount of ammonia obtained upon distillation is 
usually small it is quite necessary to avoid an excess of the mag¬ 
nesium salt and also the phosphate, for the reason that magne¬ 
sium phosphate is almost sure to be precipitated. This latter 
salt appears as an amorphous deposit and if conditions are favor¬ 
able it may eventually crystallize in star-like crystal aggregates, 
distinct, it is true, from the ammonium magnesium phosphate, 
yet very apt to confuse the beginner. 
If the phosphate test be applied directly to a solution of the 
unknown salt it must be remembered that both phosphates and 
hydroxides of a number of elements will probably be precip¬ 
itated. 
EXPERIMENTS. 
Test as above for the presence of NH4 in several different salts containing this 
radical. 
CALCIUM. 
Crystal Forms and Optical Properties of Common Salts 
of Calcium. 
A. ISOTROPIC. 
(No common salts.) 
