84 THE ATOMIC WEIGHTS. 



LITHIUM. 



The earlier determinations of the atomic weight of lithium by Arfved- 

 son, Stromeyer, C. G. Gmelin, and Kralovanzky were all erroneous, 

 because of the presence of sodium compounds in the material employed. 

 The results of Berzelius, Hagen, and Hermann were also incorrect, and 

 need no further notice here. The only investigations which we need to 

 consider are those of Mallet, Diehl, Troost, Stas, and Dittmar. 



Mallet's experiments* were conducted upon lithium chloride, which 

 had been purified as completely as possible. In two trials the chloride 

 was precipitated by nitrate of silver, which was collected upon a filter 

 and estimated in the ordinary way. The figures in the third column 

 represent the LiCl proportional to 100 parts of AgCl : 



7.1885 grm. LiCl gave 24.3086 grm. AgCl. 29.606 



8.5947 " 29.0621 29.574 



In a third experiment the LiCl was titrated with a standard solution 

 of silver. 3.9942 grm. LiCl balanced 10.1702 grm. Ag, equivalent to 

 13.511 grm. AgCl. Hence 100 AgCl = 29.563 LiCl. Mean of all three 

 experiments, 29.581, .0087. 



Diehl.f whose paper begins with a good resume of all the earlier 

 determinations, describes experiments made with lithium carbonate. 

 This salt, which was spectroscopically pure, was dried at 130 before 

 weighing. It was then placed in an apparatus from which the carbon 

 dioxide generated by the action of pure sulphuric acid upon it could be 

 expelled, and the loss of weight determined. From this loss the follow- 

 ing percentages of C0 2 in Li 2 C0 3 were determined : 



59.422 

 59.404 

 59.440 

 59.401 



Mean, 59.417, .006 



Diehl's investigation was quickly followed by a confirmation from 

 Troost.J This chemist, in an earlier paper, had sought to fix the atomic 

 weight of lithium by an analysis of the sulphate, and had found a value 

 not far from 6.5, thus confirming the results of Berzelius and of Hagen, 

 who had employed the same method. But Diehl showed that the BaS0 4 

 precipitated from Li. 2 S0 4 always retained traces of Li, which were recog- 



* Silliman's Amer. Journal, November, 1856. Chem. Gazette, 15, 7. 



f Ann. Chem. Pharm., 121, 93. 



JZeit. Anal. Chem., i, 402. 



I Annales d. Chim. et d. Phys., 51, 108. 



