i8o MICRO-CHEMISTRY [ CH. \'I 



EXAMPLES ILLUSTRATING THE 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 ) : ..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 7H.,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 lotLO. Borax. 

 Potassium ferricyanid. 



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. 



AN EXERCISE FOR PRACTICE 



" Take a fragment of ammonium chlorid, dissolve in a tiny drop of water 

 on a slide and try to obtain distinct well formed crystals. Neither slow nor 

 rapid evaporation nor recrystallization by breathing on the preparation will 

 yield satisfactory crystals." 



Place a small drop of water on a glass slide, add Ferric chlorid until the 

 drop is distinctly yellow. Stir. At the center of the drop add two or three 

 tiny fragments of Ammonium acetate. The preparation must not be warmed- 



