1904.J SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. 143 



Stated that when hexachloride is directly decomposed with water 

 and the resulting acid ignited to oxide, the latter will contain chlo- 

 rine which cannot be expelled by heat. We had hoped to pursue 

 this method, but as it had the condemnation of so high an authority 

 the hexachloride was introduced into freshly distilled ammonia 

 water, contained in a weighed platinum dish, with the expectation 

 of eventually getting ammonium tungstate anci chloride which 

 would leave the trioxide upon ignition. Experience showed that 

 the quantity of the resulting ammonium chloride was so gre.at that 

 even with the most careful ignition there was much danger of 

 expelling mechanically appreciable amounts of the oxide. Nor 

 was it forgotten that it is very doubtful whether from such a mix- 

 ture the chlorine could be completely removed by heat. 



The treatment of the hexachloride directly with nitric acid was 

 also found impracticable. 



In spite of Roscoe's objection to the decomposition with water 

 it was believed that the transposition could be carried out. 

 Five glazed No. 2 porcelain crucibles of 40CC. capacity were 

 selected, thoroughly cleansed and ignited, allowed to cool in 

 vacuum desiccators and weighed upon a specially constructed 

 Troemner balance, sensitive to ^j^^ of a milligram. There was next 

 introduced into each one of them tungsten hexachloride from a 

 weighing bottle which was reweighed after the removal of each 

 portion. The crucibles with their chloride content were placed on 

 water-baths and cold distilled water introduced into each. When 

 the volume of water was insufficient for the quantity of chloride 

 sufficient heat was generated by the reaction to make the water boil 

 and spattering followed. At 60° the decomposition proceeded 

 quietly to the hydrated trioxide, which at the beginning had a 

 slight greenish-yellow color, due probably to imperfect decomposi- 

 tion, as mentioned by Roscoe, but this tint disappeared as the 

 hydrochloric acid was expelled. When the mass was perfectly dry 

 a few drops of pure concentrated nitric acid was introduced from a 

 pipette upon the trioxide. Instantly any green tint vanished and 

 was replaced by a rich orange-yellow color. The excess of nitric 

 acid was slowly evaporated away and the oxide assumed a pale 

 yellow hue. 



The crucibles were now removed from the water-bath, and after 

 careful drying were ignited for half an hour to a dull red heat, then 

 allowed to cool in the desiccator, and at the expiration of an hour 

 and a half were weighed. 



