126 SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTE>''. [April?, 



ner, to the methods and to the conclusions of those who advocated 

 the higher value (184.92). It is not necessary here to enter into a 

 detailed review of Schneider's second and later paper. Briefly, he 

 very much doubted whether it was the complete removal of any 

 molybdenum content from the tungstic acid which occasioned the 

 rise in the atomic number. He also entertained grave doubts as to 

 whether, in the methods employed, there were not sources of error 

 which escaped these chemists. The small quantities of material 

 used by Pennington, Smith and Desi were, in the opinion of 

 Schneider, contributory sources of error. 



The problem, attracting new attention to itself in this laboratory, 

 led to further studies upon this subject, chief among which were the 

 painstaking investigations of Hardin, extending over several years. 

 Reference to these will show that few points of inquiry escaped this 

 investigator, and one can readily comprehend the spirit which 

 prompted him to say in his final contribution on this subject : 



*' So far as known there is no perfectly reliable method for the 

 determination of this constant. The method of reduction and 

 oxidation is probably more accurate than any of the other methods 

 which have been employed. The results obtained by it vary about 

 one unit and even more in exceptional cases." 



In our frequent discussions on this topic, it did seem as if search 

 for new methods was absolutely required ; that these alone might be 

 expected to settle the difficulty once for all. Taylor, engaged at 

 the time in this laboratory upon the ammonium tungstates, noticed 

 that ignited tungsten trioxide, when dissolved in a solution of pure 

 sodium carbonate, left a white flocculent residue. When dissolved 

 in potassium hydroxide, this residue was not so evident, and in his 

 thesis (University of Penn'a, 1901) he continues: 



*' On standing a few hours in sodium carbonate, this residue turned 

 reddish-brown. On treatment with hot concentrated hydrochloric 

 acid, it (having been previously washed) broke down into tungstic 

 acid, and the filtrate contained the chlorides of iron and manganese. 

 To ascertain if the original ammonium tungstate would reveal the 

 presence of these impurities, it was dissolved in water, feebly acid- 

 ulated with hydrochloric acid, and ammonium sulphocyanate 

 added. No coloration was produced. Another portion of the 

 solution was boiled with hydrochloric acid, the tungstic acid pre- 

 cipitated, and now the filtrate easily showed the presence of iron. 



**The residue, insoluble in sodium carbonate, appears to be a 

 tungstate of iron and manganese, which probably existed in the 



