406 
ELEMENTARY CHEMICAL MICROSCOPY 
to small bulk, acidified with acetic acid, a trace of sulphuric 
acid added and into the drop, a drop of silver nitrate is caused 
to flow. Silver sulphate will first separate in its characteristic 
form but will be colored yellow or red through the solid solution 
of silver chromate in it. Later the red-brown or blackish crys¬ 
tals of silver chromate appear. 
EXPERIMENTS. 
a. Look over notebook records of experiments made under Silver—Exps., 
Method B, page 382. Similar crystals will be obtained upon testing for Cr with 
AgNOs. 
b. Test for Cr in several different Cr compounds by Method B. 
c. Test by Method B in Cr salts, mixed with Al, Ee, Cu, Ni. 
d. Test for Cr in chrome iron. 
MANGANESE. 
Crystal Forms and Optical Properties of Common Salts 
of Manganese. 
A. ISOTROPIC. 
B. ANISOTROPIC. 
Hexagonal. 
Tetragonal. 
Orthorhombic. — Potassium permanganate. 
Monoclinic. — Acetate (ous); chloride (ous); am¬ 
monium-manganous sulphate; potassium- 
manganous sulphate; sodium-manganous 
sulphate. 
Triclinic. — Sulphate (ous). 
DETECTION. 
A. With Manganous Salts Oxalic Acid or Primary Potassium 
Oxalate forms Characteristic Crystals of Manganous Oxalate. 
Obtain a thin uniform film of dry potassium oxalate upon 
the slide; Method IV, page 303. Draw across this film the 
neutral solution of the material to be tested or a solution slightly 
acidified with acetic acid. Six-armed stars of MnC204 • 3 H2O 
separate. These stars result from the intersection of thin twinned 
prisms. They polarize strongly, extinguish parallel to their 
length and exhibit brilliant polarization colors. 
