398 
EI.EMENTARY CHEMICAL MICROSCOPY 
precipitate first appears, changing in part into crystalline grains 
and yellowish or reddish brown crystallites. 
By Means of Magnesium Chloride in Ammoniacal Solution. 
To the test drop add ammonium hydroxide, then apply the 
magnesium chloride by Method 7 , page 299. 
Ammonium magnesium arsenate, NH4MgAs04-6 H2O, sepa¬ 
rates in the same forms as those described for ammonium mag¬ 
nesium phosphate (q.v.) with which it is isomorphous, as also 
with the compounds NH4ZnP04 • 6 H2O and NH4ZnAs04 • 
6 H2O. A little NH4CI should be present in both drops. 
ARSENITES. 
By Means of Silver Nitrate. 
Apply the reagent by Method 7 , p. 299, to the ammoniacal drop. 
Lemon yellow silver arsenite is immediately precipitated first 
as an amorphous mass, later crystallizing in a variety of forms. 
The first crystals appear as exceedingly tiny acicular crystals in 
masses, stars and crosses, later as fusiform grains, and still later 
as thin rods with notched ends, or long irregular acicular prisms. 
Eventually some oxidation takes place and there will appear 
crystals of silver arsenate. Silver arsenite is soluble in acids 
and in ammonium hydroxide, hence the amorphous precipitate 
partially redissolves. 
EXPERIMENTS. 
a. Test by Method A the following: solutions of AS2O3; of NaAs02; of 
H2KASO4; one drop of commercial H2SO4; one drop of commercial HCl; trying 
first the AgNOs crystal and then the HgBr2 fiber. 
b. Test the above compounds by Method B. 
c. Test the same compounds with AgNOs; and finally with ZnCU. 
ANTIMONY. 
Crystal Forms and Optical Properties of Common Salts 
of Antimony. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. — Red tri-iodide; strontium-antimonyl 
tartrate; lead-antimonyl tartrate. 
