138 THE ATOMIC WEIGHTS. 



[ii tliree of these experiments the MgO was treated with H.^SO^, and 

 converted, as by Jacquelain and by Bahr in tbeir later researches, inta 

 MgSO^. One hundred })arts of MgO gave of MgSO^ as follows : 



1.9872 gim. MgO gave 5.8995 gi 111. MgSO^. 296.875 



1.7464 " 5-'783 " 296.513 



, i.74'8 " 5.1666 " 296.624 



Mean, 2y6.67r, zb .072 



[n 1850 tlie elaborate investigations of Marchand and Scheerer* ap- 

 peared. These chemists undertook to determine the comi)Osition 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 eacli case the im- 

 j)urities 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 CO.^, and still retains a little water ; on the other 

 hand, a minute quantity of CO^ remains even after ignition. The CO,^ 

 expelled at 300° amounted in one experiment to .054 ])er 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-^875 47-3372 .7753 



Mean, 47-3299, ± -0037 



After a))plying corrections for loss and retention of CO.^, as previously 

 indicated, the mean results of the foregoing series become — 



CO.,. MgO. FeO. 



5«-993> 47-2743 -7S60 



The ratio between the MgO and the CO,, after correcting for the iron, 

 will be considered further on. 



' Journ. fiir Prakt. Chem., 50, 385. 



