212 PROCEEDINGS OF THE AMERICAN ACADEMY. 



dredths of a milligram, although occasionally a third heating was 

 necessary to effect this result. 



That no loss of silver chloride by volatilization took place is certain 

 for two reasons. In the first place the cover of the crucible and the 

 delivery tube for the bromine when rinsed with ammonia and the 

 solution treated with a slight excess of hydrochloric acid gave no 

 visible opalescence in the nephelometer. In the second place the 

 weight of the chloride became constant without difhculty. It has 

 already been shown that silver chloride which has been fused in 

 chlorine, if subsequently heated in air, retains no excess of chlorine. ^^ 



The following vacuum corrections were applied: silver bromide, 

 + 0.000041; silver chloride +0.000071.23 ^he atomic weight of 

 chlorine referred to silver 107.930 is assumed to be 35.473. 



Aside from the close agreement of all the results of Series I, the 

 fact is to be emphasized that of the last seven analyses, which were 

 consecutive, only two differ from the average of the series, 79.953, by 

 as much as one one thousandth of a unit. Furthermore, there is no 

 evidence of any dissimilarity in the different preparations of bromine. 

 Material which has received only two distillations from a bromide gives 

 values no lower than bromine which has been thus treated four times. 

 The various specimens of silver also show no difference in purity. 



In the case of Series II, the extreme variation of the results is only 

 four thousandths of a unit, and only one of the thirteen experiments 

 yielded a value which differs from the average by more than one one 

 thousandth of a unit. 



Finally, the difference between the averages of Series I and II is 

 only seven ten thousandths of a unit. It is extremely unhkely that 

 constant errors could have affected both series equally, so that this 

 striking agreement is strong proof that both series are free from such 

 errors. 



It has already been pointed out that the average of Stas's syntheses, 

 79.954, probably represents with considerable accuracy the atomic 

 weight of bromine, and that certainly his determinations are more 

 accurate than those of later experimenters. His syntheses are few 

 in number, however, and differ among themselves by several thou- 

 sandths of a unit, so that they do not define within this amount the 

 constant in question. Their average, however, confirms the value 



22 Baxter, These Proceedings, 40, 4:12 (1904) ; Richards and Wells, Publica- 

 tions of the Carnegie Institution, No. 28, page 59. 



23 Kicliards and StuU have found tiie density of fused silver chloride to 

 be 5.5G. 



