ATOMIC WEIGHTS 215 



In three of these experiments the MgO was treated with H2SO4, and 

 converted, as by Jacquelain and by Bahr in their later researches, into 

 MgS04. One hundred parts of MgO gave of MgSO^ as follows : 



1.9872 grm. MgO gave 5.8995 grm. MgSOi. 296.875 



1.7464 " 5.1783 " 296.513 



1.7418 " 5.1666 " 296.624 



Mean, 296.671, ± .072 



Hence Mg= 24.711. 



In 1850 the elaborate investigations of Marchand and Scheerer ' ap- 

 peared. These chemists undertook to determine 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 yellow, transparent variety from 

 Snarum; second, a white opaque mineral from the same locality; and, 

 third, a very pure quality from Frankenstein. In each case the im- 

 purities were carefully determined; but only a part of the details need 

 be cited here. Silica was, of course, easily corrected for by simple sub- 

 traction 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, however, 

 that even here a correction was necessary. Magnesite, upon drying at 

 300°, loses a trace of COg, and still retains a little water; on the other 

 hand, a minute quantity of CO2 remains even after ignition. The COo 

 expelled at 300° amounted in one experiment to .054 per cent.; that 

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

 direction, and increase the apparent percentage of MgO in the magnesite. 

 On the yellow mineral from Snarum the crude results are as follows, 

 giving percentages of MgO, FeO and CO, after eliminating silica : 



CO.. MgO. FeO. 



51.8958 47.3278 .7764 



51.8798 47.3393 .7809 



51.8734 47.3154 .8112 



51.8875 47.3372 .7753 



Mean, 47.3299, ± .0037 



1 Journ. prakt. Chem., 50, SS5. 



