356 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



In 1868 the same methofl was employed by Debray.' His trioxide 

 was purified by sublimation in a platinum tube. His data are as follows : 



5.514 grm. MoO, gave 3.G67 grm. Mo. 66.503 per cent. 



7.910 " 5.265 " 66.561 



9.031 " 6.015 " 66.604 



Mean, 66.556, ± .020 



Hence Mo = 95.524. 



For the same ratio we have also a single experiment by Rammelsberg/ 

 who, closely following Dumas' method, found in molybdenum trioxide 

 66.708 per cent, of metal. As this figure falls within the limits of Dumas' 

 series, we may assign it equal weight with one experiment in the latter. 



Debray also made two experiments upon the precipitation of molyb- 

 denum trioxide in ammoniacal solution by nitrate of silver. In his re- 

 sults, as published, there is curious discrepancy, which, I have no d(uibt, 

 is due to a typographical error. These results I am therefore compelled 

 to leave out of consideration. They could not, however, exert a very 

 profound influence upon the final discussion. 



In 1873, Lothar Meyer" discussed the analyses made by Liechti and 

 Kemp * of four chlorides of molybdenum, and in the first edition of 

 this work the same data were considered in detail. The analyses, liow- 

 ever, were not intended as determinations of atomic weight, and since 

 good determinations have been more recently published, the work on 

 the chlorides will be omitted from further consideration. It is enough 

 to state here that they gave values for Mo ranging near 96, both above 

 and below that number, with an extreme range of over eight-tenths of 

 a unit. 



In 1893 the determinations by Smith and Maas appeared,^ represent- 

 ing an entirely new method. Sodium molybdate, purified by many re- 

 crystallizations and afterwards dehydrated, was heated in a current of 

 pure, dry, gaseous hydrochloric acid. The compound M0O3.2HCI was 

 thus distilled off, and the sodium molybdate was quantitatively trans- 

 formed into sodium chloride. The latter salt was afterwards carefully 

 examined, and proved to be free from molybdenum. The data, with all 

 weights reduced to a vacuum standard, are subjoined : 



1 Compt. Rend., 66, 734. 



2 Berlin Monatsbericht, 1877, p. 574. 



2 Ann. Chem. Pharm., 169, 365. 1873. 



* Ann. Chem. Pharm., 169, 344. 



' Journ. Amer. Chem. Soc, 15, 397 1893. 



