88 THE ATOMIC WEIGHTS. 



Diehl's investigation was quickly followed by a confirma- 

 tion from Troost.* This chemist, in an earlier paper,t 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 BaS04 precipitated from Li2S04 always retained traces 

 of Li, which were recognizable by spectral analysis, and 

 which accounted for the error. In the later paper Troost 

 made use of the chloride and the carbonate of lithium, both 

 spectroscopically pure. The carbonate was strongly ignited 

 with pure quartz powder, thus losing carbon dioxide, which 

 loss was easily estimated. The subjoined results were ob- 

 tained : 



.970 grm. Li^COj lost .577 grm. CO,^. 59-485 percent. 



1.782 " 1.059 " 59-427 



Mean, 59.456, zt .020 



This combined with Diehl's mean, 59.417, ±: .006, gives a 

 general mean of 59.420, ±: .0057. 



The lithium chloride employed by Troost was heated in 

 a stream of dry hydrochloric acid gas ; of which the excess, 

 after cooling, was expelled by a current of dry air. The 

 salt was weighed in the same tube in which the foregoing 

 operations had been performed, and the chlorine was then 

 estimated as silver chloride. The usual ratio between LiCl 

 and 100 parts of AgCl is given in the third column : 



1.309 grm. LiCl gave 4.420 grm. AgCI. 29.615 



2.750 " 9.300 " 29.570 



Mean, 29.5925, ± .0145 



This combined with Mallet's mean, 29.581, ± .0087. gives 

 a general mean of 59.584, dz .0075. 



Finally, we come to the work of Stas,t which was exe- 



* Zeit. Anal. Chem., i, 402. 



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



J Aronstein's Translation, 279-302. 



