266 



BAXTER,, WEATHERILL AND SCRIPTURE. 



In the foregoing tables the analyses are arranged in the order in 

 which they were carried out. A better comparison of the various 

 fractions is obtained if the results are tabulated in the order of volatil- 

 ity. The following table gives the observed atomic weights in the 

 order of decreasing volatility for the different chloride samples as well 

 as for the bromide. 



In the first three series, with the exception of Fraction 16, Series III, 

 there is unmistakable evidence of slightly increasing atomic weight 

 with decreasing volatility. It is especially noticeable that Fraction 12, 

 Series I, Fraction 20, Series II, and Fraction 21, Series III, which were 

 the third from the last, the next to the last and the last fractions 

 respectively, all give values nearly alike and markedly higher than the 

 others. As explained on page 252 this is probably due to less volatile 

 chlorides of silicon which seem to be removed with considerable 

 difficulty. The figures indicate, however, that the process of separa- 

 tion was still taking place even in the most carefully and elaborately 

 distilled material, Sample III. In Sample IV the fractionation was 

 many times as effective owing to the use of fractionating towers in 

 nearly every distillation. The greater efficiency is obvious from the 

 fact that even before the distillation was half completed, extreme 

 fractions, Nos. 1 and 14, showed no indication of a difference in compo- 

 sition, and the uniformity of all the material from that point on is all 

 that could be desired. There seems to be no question therefore that 



