MAGNESIUM. 



141 



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

 Richards' 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 SO3. This ratio he 

 measured both S3aithetically and analytically. First, magnesia from 

 various sources was converted into sulphate. The MgSO^ from 100 parts 

 of MgO is given in the third column : 



MgO. 



1 1-5635 



2 1.4087 



3 i-59'7 



4 1-4705 



5 1-4778 



6 1.6267 



7 1-3657 



8 1.9575 



9 1.6965 



10 1.86S0 



.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 f 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. Whetlier 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 : 



MgSO,. 



3-7705 

 4.7396 

 3-3830 

 4-7154 

 4.5662 

 4.5640 



3-2733 

 4.8856 

 5.fX)92 

 5-3396 



5-1775 

 5.0126 



5-0398 



.0150 



* Arch. Sci. Phj-s. et Nat. (3), 10, 206. 

 ■f Am. Chem. Journ., 15, 567. 1893. 



