156 MICRO-CHEMISTRY \.CH. VI 



It will be seen by the last paragraph that in chemistry as in 

 biology, the microscope is only an aid to investigation; it cannot take 

 the place of thorough training in the fundamentals of the subject 

 under investigation. 



229. The following list of substances is suggested by Dr. 

 Chamot for beginning practice as the results given are definite and 

 easily obtained : 



SUGGESTIONS FOR STUDY ON CRYSTAL SYSTEMS 



"Isometric. 



Sodium chlorid, potassium chlorid, potassium iodid. Strontium nitrate. 

 Barium nitrate. Lead nitrate. Potassium bromid. Sodium bromid. 



Alums crystallize in octahedra, cubes or combinations of the two. It is 

 well to recall that the alums have the general formula, M 2 (RO 4 ) 3 .N 2 RO 4 .24 

 H 2 O, where -M- can be Al, Cr, Mn, Fe, In, Ga, Tl, R ; -N- Na, K, Rb, Cs, 

 NH 4 Ag, or Tl and -R- S or Se. All alums are isomorphous. 



Tetragonal. 



Potassium copper chlorid. Ammonium copper chlorid. Urea. 

 Nickel sulfate 6H 2 O. This salt is dimorphic, crystallizing also in the 

 monoclinic system. Nickel sulfate yH 2 O is orthorhombic. 



Orthorhombic. 



Asparagin. Picric acid. Acetanilid. Resorcin. 



Mercuric chlorid. Silver nitrate. Potassium sulfate. Potassium nitrate. 

 Magnesium sulfate 7H 2 O. Potassium chromate. Sodium nitrate (also 

 Hexagonal). 



Monoclinic. 



Lactose. Napthalene. Potassium ferric oxalate. Sodium ferric oxalate. 



Potassium chlorate (sodium chlorate is Isomet. or Tetrag.) 



Lead acetate. Copper acetate H 2 O. Oxalic acid. 



Ferrous sulfate, this salt forms normally with 7 H 2 O and is then Mono- 

 clinic, but in presence of zinc sulfate becomes Orthorhombic, and in presence 

 of copper sulfate, triclinic. Sodium Sulfate ioH 2 O. Borax. Potassium ferri- 

 cyanid. 



Triclinic. 



Copper sulfate 5H 2 O. Boric acid. Potassium dichromate. 



Hexagonal. 



Lead iodid (according to Behrens PbI 2 is probably orthorhombic). 

 Sodium nitrate (also Orthorhombic). Bromoform. lodoform. 



% 230. Before performing analytical tests, it is necessary that the student 

 be familiar with the properties of crystals and also thoroughly familiar with 

 the appearance of crystals of the chlorids, nitrates, and sulfates of Sodium, 

 Potassium, and Ammonium ; since some of these salts are sure to appear in 

 almost every test drop examined. 



