136 THE ATOMIC WEIGHTS. 



In a later note* Scheerer shows that the barium sulphate of these ex- 

 periments carries down with it magnesium salts in such quantity as to 

 make the atomic weight of magnesium 0.039 too low. 



The work of Bahr, Jacquelain, Macdonnell, and Marignac, and in part 

 that of Svanberg and Nordenfeldt, also relates to the composition of 

 magnesium sulphate. 



Jacquelain's experiments were as follows : f Dry magnesium sulphate 

 was prepared by mixing the ordinary hydrous salt to a paste with sul- 

 phuric acid, and calcining the mass in a platinum crucible over a spirit 

 lamp to constant weight and complete neutrality of reaction. This dry 

 sulphate was weighed and intensely ignited three successive times. The 

 weight of the residual MgO having been determined, it was moistened 

 with sulphuric acid and recalcined over a spirit lamp, thus reproducing 

 the original weight of MgS0 4 . Jacquelain's weighings for these two 

 experiments show that 100 parts of MgO correspond to the quantities 

 of MgS0 4 given in the last column : 



1.466 grm. MgSO 4 gave .492 grm. MgO. 297.968 



.492 " MgO " 1.466 " MgSO 4 . 297.968 



Jacquelain also made one estimation of sulphuric acid in the foregoing 

 sulphate as BaS0 4 . His result (1.464 grm. MgS0 4 = 2.838 grm. BaSOJ, 

 reduced to the standard adopted in dealing with Scheerer's experiments, 

 gives for 100 parts of MgS0 4 , 193.852 BaS0 4 . If this figure be given equal 

 weight with a single experiment in Scheerer's series, and combined with 

 the latter, the mean will be 193.700, .0331. This again is subject to 

 the correction pointed out by Scheerer for magnesium salts retained by 

 the barium sulphate, but such a correction determined by Scheerer for 

 a single experiment is only a rough approximation, and hardly worth 

 applying. 



The determinations published by Macdonnell J are of slight impor- 

 tance, and all depend upon magnesium sulphate. First, the crystallized 

 salt, MgS0 4 .7H 2 0, was dried in vacuo over sulphuric acid and then de- 

 hydrated at a low red heat. The following percentages of water were 

 found : 



5^7 



51.14 



51.26 

 51.28 

 5 r - 2 9 



Mean, 51.21, .020 



*Poggend. Annalen, 70, 407. 



f Ann. Chim. Phys. (3), 32, 202. 



J Proc. Royal Irish Acad., 5, 303. British Association Report, 1852, part 2, p. 36. 



