12 MOLYBDENLM BLUE 



it soon changed to green and tinally pale yellow. It was thought 

 that this bleaching action might be due to the nitric acid in 

 the molybdate solution. This was found to be the case. Hence 

 neutral solutions of molybdate were used. These were made by 

 dissolving 5 grams of the salt in 500 c c of distilled water. 



A'lolybdenum Blue was obtained by the action of SnClj 

 in the presence of HCl, by Hydrogen sulphide from hot acid 

 solution, nascent hydrogen, sulphur dioxide, and oxalic aicd. 

 Quantities of the blue were obtained by stannous chloride and 

 Dumanski's method. These were by far the most satisfactory. 

 Dumanski dissolved 15 g of ammonium molybdate in 400 c c 

 water. To this solution 100 c c of 3 N or 4 N. H2SO4 was 

 added. The boiling solution was reduced with H2S. Samples 

 of the blue obtained by these two methods were dried at 40° 

 for some hours, put in a sealed bottle and labelled according to 

 their mode of preparation. 



In the preparation of the Blue it was found that, if the 

 amount of stannous chloride added to a constant amount of 

 the molybdate solution, were varied, the precipitated Blue 

 and the filtrate varied in color. It was noted that as the amount 

 of stannous chloride was increased, the precipitated Blue 

 became darker in color while the filtrate, instead of being blue, 

 was green or almost colorless. By adding molybdate solution 

 to this filtrate the blue color and further precipitate was ob- 

 tained. This suggested that green was further reduction pro- 

 duct as SnClz was evidently in excess. 



To prove this a few drops of hydrogen peroxide were added. 

 A blue color was obtained. Same result was obtained with 

 FeClj as oxidizing agent. \\'hen more SnCU instead of 

 H2O2 was added to the green solution, a brown color appeared. 

 When the green solution obtained with sulphur dioxide was 

 allowed to stand exposed to the air, it became blue. This 

 property was shown by the colorless solution obtained by re- 

 duction with Oxalic acid. 



