189i-] *^^* [Smith and Desi. 



The Atomic Mass of Tungsten. 



By Edgar F. Smith and En. D. Desi. 



{Read before the American Philosophical Society, November 2, 1S94). 



Most of the experiments made to determine this constant consist in re- 

 duction of the trioxide and the subsequent oxidation of the metal. Two 

 experimenters have attempted to weigh tlie water produced in the reduc- 

 tion of the trioxide. A. Riche (Annal de Ghim. et de Phys., (3) 50, 10. 

 1837) made five such trials. The atomic mass of tungsten, deduced from 

 bis experiments, equals 174 (0^=16). Three years later Bernoulli (Pogg. 

 Ann., iii, 599) made two experiments and his recorded value for the con- 

 stant is 186-|-. In both instances there is considerable variation in the 

 individual results. 



In a previous paper by Pennington and Smith a value (184.9) was 

 obtained that differs quite appreciably from that usually accepted as rep- 

 resenting the true atomic mass of the element under discussion. We have 

 undertaken in this present investigation to determine the atomic value 

 from the quantity of water formed in the reduction of the trioxide chiefly 

 for the purpose of ascertaining whether the elimination of the last traces 

 of molybdenum would likely produce the great rise in atomic mass. It 

 will be remembered that great stress was laid upon this point by Pen- 

 nington and Smith. In the preparation, therefore, of our trioxide we 

 adhered closely to their method of purification and observed all precau- 

 tions laid down by them. For details, therefore, we would refer the 

 reader to their paper. 



The hydrogen used by us in the reductions was prepared from sulphu- 

 ric acid and the purest zinc obtainable. To purify the gas it was con- 

 ducted through a series of bottles containing potassium permanganate, 

 an alkaline lead nitrate solution, silver nitrate, caustic potasli, sulphuric 

 acid, calcium chloride, and finally through a glass tube nine inches long, 

 filled with bright, polished iron wire. The latter was heated constantly 

 with a Bunsen burner. After this the gas was admitted to the tube where 

 it came in contact with the ignited trioxide, contained in a platinum boat. 

 The water produced in the reduction was collected in a weighed, glass- 

 stoppered U-tube, filled with auliydrous calcium cliloride. A similar tube 

 was attached to this to prevent absorption of moisture from the surround- 

 ing atmosphere. 



All weighings were reduced to the vacuum standard, and in the calcu- 

 lations oxygen was taken as 16 and hydrogen as 1.008 (Clarke). 



