ATOMIC WEIGHTS 213 



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 MgS04. Jacquelain's weighings for these two 

 experiments show that 100 parts of MgO correspond to the quantities 

 of MgSO^ given in the last column: 



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



.492 " MgO " 1.466 " MgSOi. 297.968 



Hence Mg = 24.444. 



Jacquelain also made one estimation of sulphuric acid in the foregoing 

 sulphate as BaSO,. His result (1.464 grm. MgS04 = 2.838 grm. BaSOJ, 

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

 gives for 100 parts of MgSO^, 193.852 BaSO.j. 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 ' are of slight impor- 

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

 salt, MgSO^.THoO, was dried in vacuo over sulphuric acid and then de- 

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



found : 



51.17 

 51.13 

 .51.14 

 51.26 

 51.28 

 51.29 



Mean, 51.21, ± .020 



Secondly, anhydrous magnesium sulphate was precipitated with barium 

 chloride. From the weight of the barium sulphate, with SOj^SO and 

 Ba = 137, Macdonnell computes the percentages of SO^ given below. I 

 calculate them back to the observed ratio in uniformity with Scheerer's 

 work : 



iProc. Roval Irish Acad., 5, 303. British Assoc. Report, 1S52, part 2, p. 36. 



