240 THE ATOMIC WEIGHTS. 



oxide thus left as residue. In the sulphate, Cr 2 (S0 4 ) 3 , the subjoined per- 

 centages of Cr 2 3 were found. The braces indicate two different sam- 

 ples of material, to which, however, we are justified in ascribing equal 

 value : 



.542 grm. sulphate gave .212 grm. Cr 2 O 3 . 39.114 per cent. ~\ 



1.337 " .523 " 39.117 " 



.5287 .207 " 39. 153 " 3 



1.033 .406 " 39o03 " ) 



.868 " .341 " 39-286 " 



Mean, 39.1946, .0280 



From the alum, NH 4 .Cr(S0 4 ) 2 .12H 2 0, we have these percentages of 

 O 2 O 3 . The first series represents a salt long dried under a bell jar at a 

 temperature of 18. The crystals taken were clear and transparent, but 

 may possibly have lost traces of water,* which would tend to increase 

 the atomic weight found for chromium. In the second series the salt was 

 carefully dried between folds of filter paper, and results were obtained 

 quite near those of Berlin. Both of these series are discussed together, 

 neither having remarkable value: 



1.3185 grm. alum gave .213 grm. Cr 2 O 3 . 1 ^> 1 55 P er cent. 



.7987 " .129 " 1 6. 151 " 



1.0185 " .1645 " 16.151 " 



1.0206 .1650 " 16.167 " 



.8765 .1420 " 16.201 " 



.7680 " .1242 " 16.172 " 



1.6720 " .2707 " 16.190 " 



.5410 .0875 <( 16.174 



1.2010 " .1940 " T 6.i53 " 



i. ooio " .1620 " 16.184 " 



.7715 " .1235 " 16.007 



1.374 " .2200 " 16.012 " 



Mean, 16.143, .0125 



The determinations made by Lefortf are even less valuable than those 

 by Moberg. This chemist started out from pure barium chromate, which, 

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

 250. The chromate was dissolved in pure 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 somewhat 

 too high. Calculated from his weighings, 100 parts of BaS0 4 correspond 

 to the amounts of BaCr0 4 given in the third column : 



* This objection is suggested by Berlin in a note upon I v efort's paper. Journ. fur Prakt. Chem. 

 71, 191. 

 t Journ. fur Prakt. Chem., 51, 261. 1850. 



