3S8 
ELEMENTARY CHEMICAL MICROSCOPY 
Orthorhombic. —Nitrate (usually M). 
Monoclinic. — Nitrate (or O). 
Triclinic. 
DETECTION. 
A. By Means of Cesium Sulphate. 
Apply the reagent by Method III, page 300. 
Cesium alum CsAl(S04)2 • 12 H2O separates in large, beauti¬ 
fully formed, brilliant, colorless octahedra, dodecahedra or in 
combinations of the cube and octahedron (isometric). Dendrites 
and many faced crystal aggregates are also frequent. 
Test drops containing cesium alum have a great tendency to 
remain in a state of supersaturation. Often a single large crystal 
only will appear. In such an event, crushing the crystal and 
drawing its fragments through the drop will almost invariably 
yield a large crop of well-formed crystals. 
Schoorl suggests keeping as a reagent a sample of pure cesium 
alum. When testing for aluminum he adds cesium sulphate (or 
chloride) and after concentration to about the point of super¬ 
saturation, the tiniest possible fragment of cesium alum is intro¬ 
duced into the preparation and instantly pressed upon and 
crushed with a platinum wire, thus seeding the drop and causing 
the immediate appearance of the alum crystals, providing of 
course that aluminum is present. 
Testing for aluminum with cesium sulphate leaves little to be 
desired as to accuracy and elegance, but requires a little practice 
to learn just the proper concentration. Too dilute a test drop 
requires very long waiting. Spontaneous evaporation leads 
almost invariably to supersaturation. Evaporation over the 
micro-flame is very unsatisfactory. On the other hand, the 
addition of the reagent to too concentrated a test drop gives 
rise to the immediate formation of dendritic masses and skeleton 
crystals. It is true that the experienced worker will usually at 
once recognize these dendrites as due to the presence of aluminum, 
but in view of the fact that beautiful and far more characteristic 
crystals can be obtained, the worker should not be satisfied with 
malformed crystals. 
