18 MOLYBDENUM BLUE 



SnCL, separated out. Three weeks later the solution was filtered. 

 The precipitate formed a gel on the filter. It turned a darker 

 brown. Lack of time prohibited further investigation. The 

 experiments showed that Blue could not be obtained except in 

 water solution. 



The Gel. — Solubility in solvents: The hydrogel pre- 

 pared by action of stannous chloride and sulphuretted hydrogen 

 was dried. The solubility of the dried gel in various solvents 

 was ascertained. It was found that the gel dissolved in water, 

 absolute alcohol and methyl alcohol. No apparent solution 

 took place when gel was shaken in ether, benzene, carbon bisul- 

 pide, acetone and chloroform. The fact that Molybdenum 

 blue is soluble in absolute alcohol is of more importance than 

 would, perhaps, be recognized at first glance. This will be dealt 

 with later. 



The negative character of the colloidal Blue was shown 

 by a modification of Cohen's apparatus. It consisted of a 

 U-tube partly filled with agar, in which sodium chloride had 

 been dissolved. The dialyzed hydrosol was poured into each arm, 

 the levels in each being the same. Platinum electrodes were im- 

 mersed in the hydrosol. A current of 1-2 mil amperes and pres- 

 sure 4 volts was passed through tube for 16 hours. At the end 

 of that time it was found that blue solution had become colorless. 

 The level of water in the cathode arm had risen. Solutions in 

 each arm were tested for oxidation or reduction. The cathode 

 arm gave negative tests. The solution from the anode tube 

 showed oxidation, due to chlorine liberated from the electrolyte 

 (NaCl). 



A solution of the hydrosol in agar was now placed in a 

 U-tube. Electrodes were immersed in gel. Potential was 

 raised to 10 volts. A current of 3 milamperes was passed through 

 tube for 16 hours. The blue migrated towards the anode. 

 This proved that hydrosol carried a negative charge. 



An experiment was undertaken to find whether the hydro- 

 sol and alcosol had the same rate of migration. Solutions of 



