464 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



applying the corresponding correction, it was subtracted from that com- 

 puted for the nitrate, and the difference added to the final weighing, in 

 order to determine the true loss of weight which corresponds to the 

 nitric pentoxide. * 



Results of the Analtsis of Caesic Nitrate. 

 O = 16.000 ; N = 14.040. 



In this case, as in all the other cases treated in this paper, the analyses 

 were consecutive, and the table contains all that were made excepting 

 such as were intentionally of a preliminary nature and not worthy of 

 detailed mention. The results will be discussed in connection with the 

 other data at the close of the paper. 



VIII. The Analysis of Caesic Bromide. 



While the preceding results seemed to be conclusive as to the atomic 

 weight of caesium, it was thought desirable to study the bromide also, 

 because this salt is capable of especially exact analysis. 



The bromide is easily prepared. In the first place, by adding to the 

 nitrate an excess of hydrobromic acid and bromine, the tribromide is 

 obtained on cooling in the form of deep orange crystals. Pure materials, 

 prepared by the well known methods of Stas, were used in this process. 

 After having been freed from chlorine and iodine the bromine was 

 redistilled five times; and the hydrobromic acid made from it was 



* Let a = weight of nitrate in air, and m — its correction to the vacuum standard ; 

 b = the weight of the oxide in air, and n — its correction to the vacuum standard ; 

 c = weight of silica. Then the weight of nitric peroxide in vacuum = true loss of 

 weight ='[a + c) + m — [(b + c) + n] = (a — b) + (m — n). 



