A Study of Molybdenum Blue, its Properties and Com- 

 position. — By Lloyd Alexander Munro, B. A., Dal- 



housie University, Nova Scotia. 



(Read 8 January, 1923) 



Introduction. — Centuries before Alolybdenum was recog- 

 nized as an element, tlie name iVlolybdos, "lieavy" had been 

 given by the Greeks to ores of lead. Until the middle of the 

 eighteenth century, Graphite or "Plumbago", as it was then 

 called, and Alolybdenite, were thought to be identical. Scheele, 

 in 1778, proved that these were different minerals. In his 

 "Treatise on Alolybdena," he Dointed out that one of these, 

 Alolybdenite, formed a "pecular white earth," when treated 

 with niiiic acid. "Black Lead" did not give a similar reaction. 

 The white precipitate from Alolybdenite was found to be acidic 

 in character. Scheele named it "Acid of Alolybdena" or "AIol- 

 ybdic Acid." The metal was isolated several years later (1790) 

 by Hjelm. He reduced Alolybdic acid by heating it with char- 

 coal. 



Alolybdenum Blue is the name given to the blue colora- 

 tion obtained when Alolybdic Acid is reduced in acid solution. 

 This reaction is one of the most characteristic tests for Aloly- 

 bdenum. In addition to this there are several other tests for 

 the element. A common one is the precipitation of curdy mass 

 in solution of Alolybdate when not too dilute. This also gives 

 a yellow-green color to the blow-pipe flame. It imparts a green 

 color to the Borax bead. 



Later work has brought to light ether tests. The Chemical 

 Abstracts (1913) give a paper on "Sensitive Reaction for the 

 Detection of Alolybdenum," (A.C.S. 3726). The presence of 

 Molybdenum was shown by a blood red color obtained by 

 KCNS in a solution of molybdate reduced by calcium chlo- 

 ride, or zinc and sulphuric acid. The test was not dependable 

 when stannous chloride was used. 



In 1912, Alelikov published a paper (Ber. 31. 2448) on 

 "Reaction for Detectionof Alolybdic Acid." The test was for 



