134 SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. [A.pril7, 



chemist tried seven different schemes in his endeavor to obtain 

 pure tungstic acid without the desired result. Accordingly, on 

 resuming this part of our study in the summer of 1902 we deter- 

 mined to eliminate every possible source of contamination from 

 the various reagents which we proposed using. Thus, fifteen liters 

 of hydrochloric acid were purified as already described. It was 

 free from every impurity, which was proved by carefully repeated 

 tests. Eighteen liters of nitric acid were distilled after the addi- 

 tion of pieces of pumice and some sodium hydrogen phosphate. 

 The product left no ponderable residue when a definite volume of 

 it was evaporated to dryness in a platinum vessel. The sodium 

 carbonate was made pure by fusing it in a platinum vessel and 

 introducing into the molten mass a small quantity of pure, precipi- 

 tated calcium carbonate v/hich dissolved ; the mass being held for 

 five minutes in the liquid state. After cooling, the fusion was 

 allowed to dissolve out in cold water. The calcium carbonate, 

 iron, etc., were filtered off and the solution evaporated to crystal- 

 lization. The sodium carbonate which separated was recrystallized 

 four times. Platinum vessels were used for the purpose. They 

 are essential. Portions of the purified salt were examined for silica 

 and iron, and their absence demonstrated. There was now every 

 reason to believe that the reagents, including the water (for it had 

 been redistilled), were pure. They contained nothing which would 

 contaminate the tungsten trioxide. Therefore, if the latter left a 

 residue upon digestion with a dilute sodium carbonate solution, that 

 residue plainly came out from the tungstic oxide. 



And now we must digress a little. Wyman experienced difficulty 

 and annoyance in his efforts to dissolve tungstic acid in ammonia 

 water. Others have had, doubtless, similar experiences. There 

 invariably remains a bluish-white mass which no amount 6f ammo- 

 nia or protracted boiling eliminates. More than a kilogram of this 

 substance had accumulated from Wyman' s work and came into our 

 possession. Its bluish-green tint suggested the presence in it of 

 some reduction product, probably occasioned by the hydrochloric 

 acid. We accordingly projected the mass into boiling concen- 

 trated nitric acid. A violent evolution of chlorine immediately 

 followed and continued until the material had acquired a rich 

 yellow color. Whence came the chlorine? More of the blue 

 residue was dried at 100°, then heated upon a platinum foil. Great 

 volumes of ammonium chloride were expelled, leaving pale-yellow 



