MOLYBDENUM. 



251 



not necessary to cite them in this discussion. We again encounter in 

 these figures the same source of constant error which apparently vitiates 

 the preceding series, namely, the possible volatilization of the trioxide. 

 Here, also-, such an error would tend to reduce the atomic weight of 

 molybdenum. 



From the CO 2 series Mo 91.25 



From the MoS., series. 



Mo = 92.49 



Berlin,* a little later than Svanberg and Struve, determined the atomic 

 weight of molybdenum by igniting a molybdate of ammonium and 

 weighing the residual MoO 3 . Here, again, a loss of the latter by vola- 

 tilization may (and probably does) lead to too low a result. The salt 

 used was (Nll 4 ) 4 Mo ft O tt .BH,O, and in it these percentages of Mo0 3 were 

 found : 



81.598 



81.612 



81.558 



81-555 



Mean, 81.581, .0095 



Hence Mo = 91.559. 



Until 1859 the value 92 was generally accepted on the basis of the fore- 

 going researches, but in this year Dumas f published some figures tend- 

 ing to sustain a higher number. He. prepared molybdenum trioxide 

 by roasting the disulphide, and then reduced it to metal by ignition in 

 hydrogen. At the beginning the hydrogen was allowed to act at a com- 

 paratively low temperature, in order to avoid volatilization of trioxide; 

 but at the end of the operation the heat was raised sufficiently to insure 

 a complete reduction. From the weighings I calculate the percentages 

 of metal in MoO 3 : 



.448 grm. MoO 3 gave .299 grm. Mo. 

 .484 " .323 



.484 .322 



.498 .332 



559 " -373 



.388 " .258 



66.741 per cent, 

 66.736 " 

 66.529 " 

 66.667 " 

 66.726 " 

 66.495 " 



Mean, 66.649, 3 



In 1868 the same method was employed by Debray.J His trioxide 

 was purified by sublimation in a platinum tube. His percentages are 

 as follows : 



5.514 grm. MoO 3 gave 3.667 grm. Mo. 

 7.910 " 5.265 



9.031 " 6.015 " 



66.503 per cent. 

 61.561 

 66.604 " 



Mean, 66.556, =b .020 



* Journ. fur Prakt. Chem., 49, 444. 1850. 

 f Ann. Chem. Pharm., 105, 84, and 113, 23. 

 J Compt. Rend., 66, 734. 



