246 THE ATOMIC WEIGHTS. 



And the ratios become 



Percent. Cr.,O. A . looAgCl : Salt. woAgCl : Cr.,O 3 . 

 19.037 139-679 26.591 



19.072 139.255 26.559 



19.059 i39- I 38 26.532 



Mean, 19.059, HZ .0074 Mean, 139.357, .1 109 Mean, 26.561, =h .01 15 



The first of these three analyses is rejected by Meineke as suspicious, 

 but for the present I shall allow it to remain. The data in the third 

 column may now be combined with the corresponding figures from the 

 normal chromate, as found by Meineke and his predecessors. 



Berlin 26.682, .0076 



Siewert, from Ag 2 Cr 2 O 7 26.525, .0340 



Meineke, from Ag 2 CrO 4 26.560, .0093 



Meineke, from Ag 2 CrO 4> 4NH 3 26.561, dr .0115 





General mean ..................... 26.620, rb .0052 



: Cr 2 O 3 : : 100 : 26.620, .0052 



Obviously, this mean is vitiated by the known error in Berlin's work, 

 the ultimate effect of which is yet to be considered. 



In all four of the salts studied by Meineke he determined volumetric- 

 ally the oxygen in excess of the normal oxides by measuring the amount 

 of iodine liberated in acid solutions. With the silver salts the process 

 was essentially as follows : A weighed quantity of the chromate was dis- 

 solved in weak ammonia, and the solution was precipitated with potas- 

 sium iodide. After the silver iodide had been filtered off, five or six 

 grammes of potassium iodide were added to the filtrate, which was then 

 acidulated with phosphoric acid and a little sulphuric. The liberated 

 iodine was then titrated with sodium thiosulphate solution, which had 

 been standardized by means of pure iodine, prepared by Stas' method, 

 From the iodine thus measured the excessive oxygen was computed, and 

 from that datum the atomic weight of chromium was found. For pres- 

 ent purposes, however, the data may be used more directly, as giving the 

 ratios I 3 : Ag 2 Cr0 4 and I, : Ag 2 Cr0 4 .4NH 3 . Thus treated, the weights are 

 as follows, reduced to a vacuum. Reckoning the salt as 100, the third 

 column gives the percentage of iodine liberated : 



Ag.fr O. I Set Free. Percentage. 



.43838 .50251 114.628 



.90258 1.03432 H4-595 



.89858 1.02980 114.603 



.89868 1.03072 T 14.693 



Mean, 114.630, .015 



