MAGNESIUM. 



141 



impurity tending to raise the apparent atomic weight of the metal. 

 Richards 1 and Parker's revision of this ratio is more satisfactory. 



Marignac, * in 1883, resorted to the old method of determination, de- 

 pending upon the direct ratio between MgO and S0 3 . This ratio he 

 measured both synthetically and analytically. First, magnesia from 

 various sources was converted into sulphate. The MgS0 4 from 100 parts 

 of MgO is given in the third column : 



MgO. MgSO. Ratio. 



4.6620 298.17 



4.2025 298.32 



4.7480 298.30 



4.3855 298.23 



4.4060 298.15 



4-8530 298.33 



4.0740 298.37 



5.8390 298.29 



5.0600 298.26 



5.5715 298.26 



Mean, 298.27, .0149 



The magnesia for experiments 1 to 5 was prepared by calcination of 

 the nitrate, that of 6 to 8 from the sulphate, and the remaining two from 

 the carbonate. But Richards and Rogers t have shown that magnesia 

 derived from the nitrate always contains occluded gaseous impurity, so 

 that the experiments depending upon its use are somewhat questionable. 

 The results tend to give an atomic weight for magnesium which is pos- 

 sibly too high. Whether the other samples of magnesia are subject to 

 similar objections I cannot say. 



Marignac's second series was obtained by the calcination of the sul- 

 phate, with results as follows : 



* Arch. Sci. Phys. et Nat. (3), 10, 206. 

 f Am. Chem. Journ., 15, 567. 1893. 



