388 ELEMENTARY CHEMICAL MICROSCOPY 



Orthorhombic. Nitrate (usually M). 

 Monoclinic. Nitrate (or O). 

 Triclinic. 



DETECTION. 



A . By Means of Cesium Sulphate. 



Apply the reagent by Method ///, page 300. 



Cesium alum CsAl(SO 4 ) 2 12 H 2 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. 



