CRYSTALLIZATION EXPERIMENTS 271 



Isometric System. 



Sodium chloride; potassium iodide; barium nitrate; ammonia alum; chrome 

 alum; arsenic trioxide; sodium chlorate (circular polarization). 

 Hexagonal System. 



Lead iodide; iodoform; cadmium iodide; normal sodium phosphate; strontium 

 chloride; strontium antimonyl tartrate; sodium nitrate. 

 Tetragonal System. 



Potassium arsenate; mercuric cyanide; potassium copper chloride; urea; 

 strychnine sulphate; primary ammonium phosphate; primary potassium phos- 

 phate. 

 Orthorhombic System. 



Ammonium sulphate; mercuric chloride; potassium antimonyl tartrate; po- 

 tassium nitrate ; potassium sulphate; sodium nitroprusside; zinc sulphate; uranyl 

 acetate. 

 Monoclinic System. 



Potassium ferrocyanide; potassium ferricyanide; sodium ferric oxalate; ammo- 

 nium persulphate; potassium chlorate; barium chloride; nickel chloride; tartaric 

 acid; saccharose; potassium magnesium sulphate. 

 Triclinic System. 



Copper sulphate; potassium bichromate; potassium persulphate; boric acid; 

 manganous sulphate. 

 Pleochroic Salts. 



Copper acetate; iodoquinine sulphate; potassium (or sodium) ferric oxalate; 

 potassium cobalt sulphate; silver bichromate; potassium chromium oxalate. 



In a watch glass place a few drops of benzene, add a few crystals of quinone, 

 stir until dissolved. Add a few crystals of resorcin, stir. Remove a drop to a 

 slide and allow it to deposit crystals by spontaneous evaporation. The crystals 

 will be found to be strongly pleochroic. 



All the compounds listed above are easily crystallizable. 

 Most of them are soluble in both hot and cold water. The 

 exceptions to this rule are: (a) strontium antimonyl tartrate 

 more soluble in ice cold water than in hot water ; (b) lead iodide, 

 cadmium iodide almost insoluble in cold water, soluble in hot 

 water, (c) iodoform, iodoquinine sulphate, insoluble in water, 

 soluble in alcohol, (d) silver bichromate practically insoluble 

 in water, soluble in dilute nitric acid or in dilute ammonium 

 hydroxide. 



All the compounds given should have yielded, under the 

 conditions of the experiments, normal, typical, well-developed 

 crystals whose habits could be easily recognized. Had we forced 

 the crystallization too rapidly, or had there been one or more 

 other compounds present, or had colloids been present such as 

 gums, resins, mucilages, etc., then instead of well formed crys- 



