MAGNESIUM. 103 



1.9872 grm. MgO gave 5.8995 gnn. MgSO^. 296.875 

 1.7464 " 5-1783 " 296.513 



I. 7418 " 5.1666 " 296.624 



Mean, 296.671, ± .072 



We have now for this ratio between MgO and MgSO^ 

 three series ; not at all concordant. We may combine them, 

 assigning to each of Jacquelain's two results a weight cor- 

 responding to one of Bahr's : 



Jacquelain 297.968, zh .0999 



Bahr 296.200, ± .0815 



Svanberg and Nordenfeldt 296.671, ±z .072 



General mean 296.806, dr .0475 



In 1850 the elaborate investigations of Marchand and 

 Scheerer* appeared. These chemists undertook to deter- 

 mine the composition of some natural magnesites, and, by 

 applying corrections for impurities, to deduce • from their 

 results the sought for atomic weight. The magnesite chosen 

 for the investigation was, first, a yelloAv, transparent variety 

 from Snarum ; second, a white opaque mineral from the 

 same locality ; and, third, a very pure cjuality from Frank- 

 enstein. In each case the impurities were carefully deter- 

 mined ; but only a part of the details need be cited here. 

 Silica was of course easily corrected for by simple subtrac- 

 tion from the sum of all of the constituents ; but iron and 

 calcium, when found, having been present in the mineral as 

 carbonates, required the assignment to them of a portion of 

 the carbonic acid. In the atomic weight determinations 

 the mineral was first dried at 300°. The loss in weight 

 upon ignition was then carbon dioxide. It was found, how- 

 ever, that even here a correction was necessary. Magnesite, 

 upon drying at 300°, loses a trace of CO2, and still retains a 

 little water; on the other hand, a minute quantity of CO, 

 remains even after ignition. The CO2 expelled at 300° 

 amounted in one experiment to .054 per cent. ; that retained 

 after calcination to .055 per cent. Both errors tend in the 



*Journ. fur Prakt. Chem.,50, 385. 



