AJOMIC WEIGHTS 343 



to thoroughly free it from moisture, had been dried for several hours at 

 250°. The chromate was dissolved in nitric acid, the barium thrown 

 down by sulphuric acid, and the precipitate collected upon a filter, dried, 

 ignited and weighed in the usual manner. The natural objection to the 

 process is that traces of chromium may be carried down with the sul- 

 phate, thus increasing its weight. In fact, Lefort's results are certainly 

 too high. Calculated from his weighings, 100 parts of BaS04 correspond 

 to the amounts of BaCrO^ given in the third column : 



1.2615 grm. BaCrO^ gave 1.1555 grm. BaSO*. 109.174 



1.5895 " 1.4580 " 109.019 



2.3255 " 2.1340 " 108.974 



3.0390 " 2.7855 " 109.101 



2.3480 " 2.1590 " 108.754 



1.4230 " 1.3060 " 108.708 



1.1975 " 1.1005 " 108.814 



3.4580 " 3.1690 " 109.119 



2.0130 " 1.8430 " 109.224 



3.5570 " 3.2710 " 108.744 



1.6470 " 1.5060 " 109.363 



1.8240 " 1.6725 " 109.058 



1.6950 " 1.5560 " 108.933 



2.5960 " 2.3870 " 108.756 



Mean, 108.9815, ± .0369 



Hence Cr= 53.03. 



Wildenstein,^ in 1853, also made barium chromate the basis of his 

 researches. A known weight of barium chloride was precipitated by a 

 neutral alkaline chromate, and the precipitate allowed to settle until 

 the supernatant liquid was perfectly clear. The barium chromate was 

 then collected on a filter, washed with hot water, dried, gently ignited, 

 and weighed. Here again arises the objection that the precipitate may 

 have retained traces of alkaline salts, and again we find deduced an 

 atomic weight which is too high. One liundred parts of BaCrO^ cor- 

 respond to BaCla as follows : 



81.87 81.57 



81.80 81.75 



81.61 81.66 



81.78 81.83 



81.52 81.66 



81.84 81.80 



81.85 81.66 

 81.70 81.85 

 81.68 81.57 

 81.54 81.83 



^ Joum. prakt. Chem., 59, 27. 



