10 MOLYBDENUM BLUE 



formation of a red ammonium pcr-m.olybdate similar to KjOj 

 ^lo O4 H. O,. 



Although the above reactions are sensitive, the standard 

 test for Molybdenum is the formation of Molybdenum Blue. 

 Nearly all text books on Inorganic Chemistry mention the blue 

 as a test for Alolybdenum or Tin, but few tell anything about 

 its properties. A still smaller number assign any formula to 

 the compound which causes coloration. Formulae suggested 

 by these writers show little agreement. 



A few extracts from well known volumes will show this 

 clearly. The "Encylopedia Brittanica," says: "ammonium 

 molybdate (NH4)ioMo240i5 with hydrochloric acid or nitric 

 acid gives a white precipitate; with reducing agents, such as 

 sulphurated hydrogen, sulphuric acid and zinc, stannous chlo- 

 ride, etc., it gives a blue coloration, which turns green and finally 

 brown." 



Holleman, (translated by Cooper, 1911), states: 



"A very characteristic test for molybdic acid is the follow- 

 ing: the substance is mixed with zinc and sulphuric acid. At 

 first a blue coloration (a Molybdate of Molybdic Oxide) appears." 



Kolbe also merely mentions the blue as a test. "If zinc 

 is added to a solution of molbydic acid a blue color is first pro- 

 duced which becomes green and finally dark brown in color, 

 due to reduction." 



Mellor, in his very readable book on "Inorganic Chemistry," 

 does not give any definite formula. "The molybdates," he 

 writes, "are reduced by zinc in acid solution to one of the lower 

 oxides, approximately M02 O3 and at the same time the color 

 of the solution changes through various shades of violet, blue 

 and black." 



Browning of Yale, in his book "The Rarer Elements," 

 does not suggest the formula for Molybdenum Blue. 



Finally, Roscoe and Schorlemmer in their "Treatise on 

 Chemistry," Vol. II. 1044 (1917), give the following: 



