Dinwiddie — Separation of Magnesium. 



663 



the determinations, portions of the magnesium chloride solution 

 (15 cm3 -20 cm3 ) were measured out and carefully weighed, lithium 

 chloride was introduced in the amounts stated, 25 cm3 of 93 per 

 cent alcohol and 50 cmS of the precipitating mixture were added, 

 the mixture was stirred vigorously (for perhaps a minute) and 

 set aside for live hours or more. The supernatant liquid was 

 decanted upon asbestos in the perforated crucible (weighed), 

 the precipitate was stirred up with more of the precipitating 

 mixture and allowed to settle, and the liquid was again decanted 

 upon the same asbestos filter. In the cases in which a single 

 precipitation was employed, the precipitate was simply trans- 

 ferred to the filter and washed with the precipitating mixture, 

 and ignited to constant weight. When two precipitations were 

 made, in order to remove possible inclusions of lithium salt 

 from the precipitated ammonium magnesium carbonate, the 

 precipitate was dissolved in the least necessary amount of 

 hydrochloric acid, the solution was diluted to a volume of 10 c,n3 , 

 13 cm3 -15 cm3 of 93 per cent alcohol and 50 cm3 of the precipitant 

 were added, and the precipitate was transferred, washed, and 

 ignited as described. 



The following tables show the results obtained with solutions 

 of magnesium chloride with and without the addition of lithium 

 chloride in varying amount. The mean of the three deter- 

 minations in which the solution contained no lithium salt was 

 taken to fix the value of the magnesium solution and by com- 

 parison with this standard the errors of the single determina- 

 tions were computed. 







Table I. 





Standardization 



of the Magnesium Solution. 



Solution 

 MgCl 2 



MgO 

 found 



MgO Average MgO 

 found per per grm. of 

 grm. of solution solution 



grm. 



grm. 



grm. grm. 



20-4071 

 20-3956 

 15-4271 



0-2788 

 0-2779 

 0-2108 



0-013662* ) 



0-013626* V 0-013651 



0'013664f ) 



* One precipitation. 



\ Two precipitations : washings made with precipitant saturated \s 

 precipitate. 



It will be seen that while the separation of 0*2 grm. of 

 magnesium oxide from lithium amounting to - 5 grm. of the 

 chloride or 0'083 grm. of the element may be reasonably good 

 in a single precipitation, the ammonium magnesium carbonate 

 only once precipitated is largely contaminated, presumably 



