362 ELEMENTARY CHEMICAL MICROSCOPY 



To complete the test add a fragment of rubidium chloride, 

 stir, add a drop of water and allow a drop of perchloric acid to 

 flow into the drop. Crystals of rubidium perchlorate are imme- 

 diately formed, taking up the permanganate in solid solution and 

 yielding pink or purple crystals. 



EXPERIMENTS. 



Test this method first upon pure Mn salts, then upon mixtures of other elements 

 with Mn. 



IRON. 



Crystal Forms and Optical Properties of Common Salts 

 of Iron. 



A, ISOTROPIC. Iron alums (I). 



B. AN ISOTROPIC. 



Hexagonal. Chloride (when sublimed). 



Tetragonal. 



Orthorhombic. Ammonium-ferric chloride; oxa- 

 late (ous). 



Monoclinic. Sulphate (ous); 1 ammonium-ferrous 

 sulphate; sodium-ferric oxalate ; potassium- 

 ferric oxalate. 



Triclinic. 



DETECTION. 



A . By Means of Potassium Ferrocyanide. 



To the test drop, apply a fragment of the reagent by 

 Method ///, page 252. 



A dark blue precipitate or color indicates iron. The precip- 

 itate is soluble in alkalies, insoluble in acids. It is therefore 

 always best to acidify with hydrochloric acid before adding the 

 ferrocyanide. 



The presence of much copper may seriously interfere with the 

 test because of the formation of brown copper ferrocyanide. 



1 But if magnesium sulphate is present, orthorhombic. 



