ATOMIC WEIGHTS 



349 



From Meineke's figures Cr=: 52.10, 52.04 and 52.14. 

 With the ammonio-chromate Meineke found as follows 



And the ratios become — 



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,Cr„0, 26.525, ± .0340 



Meineke, from Ag.CrOi 26.560, ± .0093 



Meinel^e, from Ag,Cr04.4NH3. . . 26.561, ± .0115 



General mean 26.620, ± .0052 



4AgCl:Cr203: : 100: 26.620, ± .0052 



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

 the ultimate effect of which is serious. 



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

 ally file 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 Avas 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 



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