244 THE ATOMIC WEIGHTS. 



Combining, as before, with Berlin's single result, giving the latter equal 

 weight with one of these, we have a general mean of 35.236, .0335. 



For the ratio between silver chloride and chromic oxide, Siewert's two 

 analyses of the dichromate come out as follows. For 100 parts of AgCl 

 we have of Cr 2 8 : 



Mean, 53.049, .068 



This figure, reduced to the standard of Berlin's work on the mono- 

 chromate, becomes 26.525, .034. Berlin's mean was 26.682, .0076. 

 The two means, combined, give a general mean of 26.676, .074. 



By Baubigny * we have only three experiments upon the calcination 

 of anhydrous chromic sulphate, as follows : 



1.989 grm. Cr 2 (SO 4 ) 8 gave .7715 grm. Cr. 2 O 3 . 38.788 per cent. 



3.958 " 1.535 " 38.782 " 



2.6052 1.0115 " 38.826 " 



Mean, 38:799, .0092 



Moberg found for the same ratio the percentage 39.195, .028. The 

 general mean of both series, Moberg's and Baubigny's, is 38.838, .0087. 



In Rawson's work f ammonium dichromate was the substance studied. 

 Weighed quantities of this salt were dissolved in water, and then reduced 

 by hydrochloric acid and alcohol. After evaporation to dryness the mass 

 was treated with water and ammonia, reevaporated, dried five hours at 

 140, and finally ignited in a muffle. The residual chromic oxide was 

 bright green, and was tested to verify its purity. The corrected weights 

 are as follows : 



Am^Cr^O-. Cr. 2 O s . Percent. Cr. 2 O 3 . 



1.01275 -61134 60.365 



1.08181 .65266 60.330 



1.29430 -78090 60.334 



1.13966 .68799 60.368 



98778 .59595 60.332 



1.14319 .68987 60.346 





Mean, 60.346, .0046 



Latest in time and most elaborate of all, we come to the determinations 

 of the atomic weight of chromium made by Meineke,J who studied the 

 chromate and ammonio-chromate of silver, and also the dichromates of 

 potassium and ammonium. For the latter salt he measured the same 

 ratio that Rawson determined, but by a different method. He precipi- 



*Compt. Rend., 98, 146. 



tjourn. Chem. Soc., 55, 213. 



t Ann. d. Chem., 261, 339. 1891. 







