1904.] SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. 185 



colored tungsten trioxide. An analysis of a portion of the dry, 

 bluish material was made, when 5.48% of NH^ and 9.65% of CI 

 were found. The presence of this amount of foreign substance 

 could only be accounted for on the assumption that in the libera- 

 tion of tungstic acid from ammoniacal solutions of ammonium tung- 

 state with hydrochloric acid portions of the latter and of the 

 ammonium chloride were so combined that no amount of washing 

 would remove them. They are retained, and firmly, by the tung- 

 stic acid. Let those who question this examine the white, slimy 

 residue which appears on attempting the solution of tungstic acid 

 in ammonia. Most of us have quieted our consciences on this 

 point by asserting that such residues are "those persistently insolu- 

 ble paratungstates." If the solution from such residues be repre- 

 cipitated with hydrochloric acid quantities of insoluble bodies again 

 appear. These are beyond question ammonium chlorinated tung- 

 stic acid derivatives which even prolonged boiling with concentrated 

 acids will not change to the yellow acid. They merit further 

 study. 



The preceding experience emphasized the necessity of removing 

 all the ammonium chloride in tungstic acid if the precipitation 

 method of purification was to be pursued. This was done in the 

 following way : two to three liters of concentrated nitric acid, 

 diluted with water to half their volume, were heated in a large porce- 

 lain dish until it began to fume strongly, when 25CC. of pure hydro- 

 chloric acid and three kilograms of dry and fairly pure ammonium 

 tungstate were added. Vigorous action set in and volumes of 

 decomposition gases escaped. The mixture was constantly stirred 

 during the operation. As soon as the action diminished, ten to fif- 

 teen cubic centimeters of pure hydrochloric acid were introduced at 

 intervals. As the decomposition approached completion, the yellow 

 tungstic acid lost its porous character and collected as a heavy granu- 

 lar powder upon the bottom of the dish, but it was heated with occa- 

 sional stirring for a period of from three to four hours. At the 

 expiration of that time, there remained only tungstic acid and 

 nitric acid with traces of chlorine and ammonia. The tungstic acid 

 was washed by decantation with pure distilled water until the tung- 

 stic acid suspended in the solution subsided very slowly, and the 

 wash-water from, it showed but a faint acid reaction. The subsided 

 yellow-colored acid was placed in a porcelain dish, hot distilled 

 water was poured over it and ammonia was conducted into the solu- 



