ATOMIC WEIGHTS 357 



.70793 .40182 56.760 



1.26347 .71695 56.745 



1.15217 .65367 56.734 



.90199 .51188 56.750 



.81692 .46358 56.747 



.65098 .36942 56.748 



.80563 .45717 56.747 



Mean, 56.745, ± .0017 



Hence Mo = 96.055. 



In 1895, Seubert and Pollard ' determined the atomic weight of mo- 

 lybdenum by two methods. First, the carefully purified trioxidc, in 

 weighed amounts, was dissolved in an excess of a standard solution of 

 caustic soda. This solution was standardized by means of hydrochloric 

 acid, Avhich in turn had been standardized gravimetrically as silver 

 chloride. Hence, indirectly, the ratio 2AgCl : MoO, was measured. Sul- 

 phuric acid and lime water were also used in the titrations, so that the 

 entire process was rather complicated. Ignoring the intermediate data, 

 the end results, in weights of MoO, and AgCl, were as follows. The third 

 column gives the M0O3 proportional to 100 parts of AgCl: 



Mean, 50.202, ± .0018 



Hence Mo = 95.92. 



The second method adopted by Seubert and Pollard was the old one 

 of reducing the trioxide to metal by heating in a current of hydrogen. 

 The weights and percentages of metal are subjoined : 



Zeitsch. anorg. Chem., 8, 434. 1895. 



