T B A N S A C T I N S. 



I. — The Atomic Weight of Tungsten. By John Waddell, B.A., D.Sc. 



(Read 7th June 1886.) 



From the results obtained by Berzelius in his experiments with tungsten, 

 the number 189 "28 is calculated as the atomic weight of that metal. Many 

 later investigations have been made, in which uniformly a lower figure was 

 arrived at, in the majority of cases very nearly 184, which has therefore been 

 regarded as the atomic weight. 



Some of the determinations were made with a special view to the support 

 or overthrow of a theory. Dumas, for instance, wished to discover whether the 

 atomic weight of tungsten was exactly double that of molybdenum. In such 

 cases it would be natural to suppose that special care would be taken to 

 secure purity of materials. Dumas obtained the numbers 96 and 184 as the 

 atomic weights of molybdenum and tungsten, but he seems to have distrusted 

 his results ; for he remarks — " Is it necessary, however, to conclude from this 

 discussion, that some simple ratios of the kind which one used to admit between 

 molybdenum and tungsten cannot exist? I do not think so " {Ann. Chim. Phys., 

 [3] 55, 144). 



In studying the literature of the subject, I felt that no security was afforded 

 by the various experimenters of the purity of the compounds made use of by 

 them. Scheibler (Jour. Prac. Chem., 83, 273), apparently considers a single 

 recrystallisation of the sodium salt all that is necessary. This salt was used as 

 a starting point, and though the further working up into barium metatungstate 

 may have tended to purification, Scheibler certainly does not prove that he 

 has thus freed his tungsten from molybdenum and silicon. Bernoulli (Pogg. 

 Ann., Ill, 573) considered that he had obtained pure tungstic acid, though he 

 gives no indication of an attempt to free from molybdenum. He prepared his 

 tungstic acid from wolfram, which contained silica and niobic acid, from which 



VOL. XXXIII. PART I. A 



