240 THE ATOMIC WEIGHTS. 



oxide thus left as residue. In the sulphate, Cr./SOJj, the subjoined per- 

 centages of Cv.fis were found. The braces indicate two different sam- 

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

 value : 



.542 gim. sulphate gave .212 grm. Cr^O,. 39- 114 per cent. "^ 



1.337 " -523 " 39- H7 " y 



.5287 " .207 " 39.153 " 3 



1.033 " .406 " 39-303 " ] 



.868 " .341 " 39.286 " 



Mean, 39.1946, zb .0280 



From the alum, NH^.Cr(SOj2.12H.^O, we have these percentages of 

 CrjOg. The first series represents a salt long dried under a ])ell 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 l^etween 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.,0.5. '6.155 P^'' cent. 



.7987 " .129 " 16.151 " 



1. 0185 " .1645 " 16. 151 " 



1.0206 " .1650 " 16.167 " 



.8765 " .1420 " 16.201 " 



.76S0 " .1242 " 16.172 " 



1.6720 " .2707 " 16.190 " 



.5410 " .0875 " 16.174 



I. 2010 " .1940 " 16.153 " 



I. 0010 " .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 BaSO^ correspond 

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



* This objection is suggested by Berlin in a note upon I^efort's paper. Journ. fiir Prakt. Cheni., 

 71, 191. 

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



