RICHARDS AND PARKER. ATOMIC WEIGHT OF MAGNESIUM. 73 



have sliowu itself iu opalescence. As a proof of this it may be stated 

 that iu experiment No. 12 of Series III. there was a perceptible cloudiness 

 upon the solution of the magnesic chloride in water, owing to a known 

 access of a trace of aqueous vapor, caused by a momentary stoppage of 

 the current of nitrogeu. This result is, however, scarcely at all different 

 from the others. 



"With legard to the possible retention of amnionic chloride by the 

 majrnesium salt, it may be said : first, that none could be detected by 

 means of a Nessler solution ; and, secondly, that even if a small amount 

 had been retained, it would have made but a very slight difference in 

 the final result. 



Our result is essentially the same, no matter whether the chlorine is 

 weiidied as arijentic chloride (Series I.), or the amount of silver neces- 

 sary to precipitate it is found (Serifs III. and IV.). This fact is satis- 

 factory evidence that that silver and chlorine were both pure, as well 

 as that no magnesic chloride was occluded by the argentic chloride. 

 Thus : — 



From the ratio 2 AgCl : MgCls (Series I.), Mg = 24.369. 

 " " 2 Ag : MgCla (Series III.), Mg = 24.365. 

 « « 2Ag : MgCla (Series IV.), Mg = 24.362. 



Upon comparing these figures with the older ones, they are seen to 

 agree surprisingly with Marignac's value obtained from work upon 

 magnesic oxide and sulphate (Mg = 24.37). Burton and Vorce's syn- 

 theses of magnesic oxide gave a lower value for magnesium (24.28); 

 but if these were corrected for a probable amount of gases in the mag- 

 nesic oxide, the result would probably be close to the present one. The 

 analytical chemist should not forget that the value 24.36 is one and a 

 half per cent higher than the round number 24, which has been so com- 

 monly accepted. 



For reasons which must be manifest to any careful reader of the fore- 

 going paper, we accept the value given by the fourth and last of our 

 series as representing the most probable atomic weight of magnesium. 

 It remains only to state this result in terms of the usual unfortunately 

 varying standards of reference used by the scientific world. 



If O = 16.000, Mg = 24.362. 

 If = 1.5.96, Mg = 24.301. 



IfO = 15.88, Mg = 24.179. 



Cambridge, May 1, 1896. 



