250 THE ATOMIC WEIGHTS. 



MOLYBDENUM. 



If we leave out of account the inaccurate determination made by 

 Berzelius,* we shall find that the data for the atomic weight of molyb- 

 denum lead to two independent estimates of its value one near 92, the 

 other near 96. The earlier results found by Berlin and by Svanberg and 

 Struve lead to the lower number; the more recent investigations, to- 

 gether with considerations based upon the periodic law, point conclu- 

 sively to the higher. 



The earliest investigation which we need especially to consider is that 

 of Svanberg and Struve. f These chemists tried a variety of different 

 methods, but finally based their conclusions upon the two following : 

 First, molybdenum trioxide was fused with potassium carbonate, and 

 the carbon dioxide which was expelled was estimated ; secondly, molyb- 

 denum disulphide was converted into the trioxide by roasting, and the 

 ratio between the weights of the two substances was determined. 



By the first method it was found that 100 parts of MoO 3 will expel the 

 following quantities of C0 2 : 



3L4954 

 3 * -3749 

 31-4705 



Mean, 31.4469, .0248 



The carbon dioxide was determined simply from the loss of weight 

 when the weighed quantities of trioxide and carbonate were fused to- 

 gether. It is plain that if, under these circumstances, a little of the 

 trioxide should be volatilized, the total loss of weight would be slightly 

 increased. A constant error of this kind would tend to bring out the 

 atomic weight of molybdenum too low. 



By the second method, the conversion by roasting of MoS 2 into Mo0 3 , 

 Svanberg and Struve obtained these results. Two samples of artificial 

 disulphide were taken, A and B, and yielded for each hundred parts the 

 following of trioxide : 



89-79191 A 

 89.7291 / 



89.6436] 

 89.7082 I 

 89.7660 j-B. 

 - 89.7640 | 

 89-8635] 



Mean, 89.7523, .0176 



Three other experiments in series B gave divergent results, and, al- 

 though published, are rejected by the authors themselves. Hence it is 



* Poggend. Annalen, 8, i. 1826. 



t Journ. fur Prakt. Chem., 44, 301. 1848. 



