1904.] SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. 131 



which in the previous experiments in this paper gave values rang- 

 ing from 182.24 to 184.82, and which was known to contain iron, 

 maganese, and probably molybdic acid : 



Weight of Weight of Weight of 



Na^CO^ WO^ CO^ Atomic Weight 



grams. ' grams. grams. of Ttiiigsten, 



(i) 2.7 2,0802 0-3952 183,60 



(2) 2.3 2,1937 0,4173 183.30 



(3) 3-5 4.0818 0.7762 183.38 



(4) 3-^ 3-3629 0,6394 183.41 



" These numbers, in that they indicate the atomic weight of tung- 

 sten, are worthless ; in that they show promise for the new method, 

 are of value. The presence of impurity would lower the result ; 

 what value the method will give for pure material can only be con- 

 jectured." 



Taylor's experience re-emphasized the absolute necessity of satis- 

 fying ourselves beyond every reasonable doubt that the material for 

 the atomic weight determinations was pure ; at least as pure as the 

 means at hand would furnish. The admission of Schneider that 

 his purest substance contained traces of impurity, insoluble in 

 caustic potash, and Taylor's discovery that every sample of tung- 

 sten trioxide tested by him gave a residue, insoluble in sodium 

 carbonate, made us very solicitous regarding the purity of all 

 material which had been used in any previous investigations, for it 

 will be found upon consulting the literature that almost every 

 experimenter was content to proceed with ammonium paratungstate 

 which was perfectly white in color. Three to five recrystalliza- 

 tions were held to be sufficient to attain that condition. 



Our doubts became so overwhelming that it was decided to begin 

 the work anew with the mineral wolframite and to ascertain, once 

 for all, what it contained in order that search might be made for 

 all such constituents, and every effort put forth to insure their per- 

 fect removal from the salts which might be experimented upon. 

 Accordingly, in the summer of 1901 large quantities of wolframite, 

 from Lawrence County, S. D., were decomposed and the resulting 

 tungstic acid converted into ammonium paratungstate. The mother 

 liquors from the salt were black in color and gave in due time the 

 interesting compound — ammonium vanadico-phosphotungstate — 

 described by us in the Jour. America?! Chemical Society, 24, 573. 

 Its discovery added, of course, vanadium and phosphorus to the 

 list of possible contaminating substances : columbic oxide, silica. 



