CHROMIUM. 243 



Siewert's determinations, which do not seem to have attracted general 

 attention, were published in 1861.* He, reviewing Berlin's work, found 

 that upon reducing silver chromate with hydrochloric acid and alcohol, 

 the chromic chloride solution always retained traces of silver chloride 

 dissolved in it. These could be precipitated by dilution with water ; 

 but, in Berlin's process, they naturally came down with the chromium 

 hydroxide, making the weight of the latter too high ; hence too large a 

 value for the atomic weight of chromium. In order to find a more cor- 

 rect value Siewert resorted to the analysis of sublimed, violet, chromic 

 chloride. This salt he fused with sodium carbonate and a little nitre, 

 treated the fused mass with water, and precipitated from the resulting 

 solution the chlorine by silver nitrate in presence of nitric acid. The 

 weight of the silver chloride thus obtained, estimated after the usual 

 manner, gave means for calculating the atomic weight of chromium. 

 His figures, reduced to a common standard, give, as proportional to 100 

 parts of chloride of silver, the quantities of chromic chloride stated in 

 the third of the subjoined columns : 



.2367 grm. CrCl s gave .6396 grm. AgCl. 37-Oo; 



.2946 " .7994 3 6 .853 



.2593 -7039 36-838 



.4935 I -3395 36.842 



.5850 " 1.5884 " 36-830 



.6511 " 1.76681 " 36.852 



.5503 " L4939I " 36.836 



Mean, 36.865, .0158 



The first of these figures varies so widely from the others that we are 

 justified in rejecting it, in which case the mean becomes 86.842, .0031. 



Siewert also made two analyses of silver dichromate by the following 

 process. The salt, dried at 120, was dissolved in nitric acid. The silver 

 was then thrown down by hydrochloric acid, and, in the filtrate, chro- 

 mium hydroxide was precipitated by ammonia. Reduced to a uniform 

 standard, we find from his results, corresponding to 100 parts of AgCl, 

 Ag 2 O 2 7 as in the last column : 



.7866 grm. Ag 2 Cr 2 O 7 gave .52202 AgCl and .2764 Cr 2 O 3 . 150.684 



1.089 " .72249 " .3840 " 150.729 



Berlin's single determination of this ratio gave 151.035. Taking all 

 three values together as one series, they give a mean of 150.816, .074. 



Siewert's percentages of Cr. 2 3 obtained from Ag 2 O 2 O r are as follows, 

 calculated from the above weighings : 



35-'39 

 35.262 



Mean, 35.2005, .0415 

 * Zeit. Gesammt. Wissenschaften, 17, 530. 



