BORON AND FLUORINE. 55 



chloride obtained was finally dried at about 350 in a current of 

 air and, therefore, must also have retained some moisture, for 

 sodium chloride, as obtained under the conditions of the experi- 

 ment must be fused for the complete expulsion of the last traces 

 of water. 10 It is practically certain, therefore, that these two 

 sources of error were operative; doubt can be entertained only 

 concerning their magnitude. Fortunately the determination of 

 the latter is not entirely beyond our reach. 



Again, the residual water in fused borax, as prepared by Ram- 

 say and Aston, is fairly constant and amounts to about 0.2 per 

 cent. It is highly probable that the percentage of water in the 

 "borax glass" used by those investigators was even greater, for 

 the low density of their vitreous borax (2.29, as against the more 

 probable value 2.357; see p. 24) is probably not without sig- 

 nificance and may be taken to show that their "borax glass" was 

 not entirely free from flaws which, in tins' case, are not only due 

 to air, but to a mixture of the latter with steam. It may be quite 

 reasonably assumed that this borax glass contained approximately 

 0.3 per cent, of water. It now remains to be seen whether we can 

 also arrive at some legitimate estimate concerning the amount 

 of moisture in the sodium chloride. This, the writers hope, can 

 also be done, with a fair degree of certainty, without drawing 

 upon the imagination. 



From Ramsay and Aston's work the ratio AgCl : NaCl may 

 be computed. The same ratio has been determined, much more 

 accurately, by Richards and Wells. The two ratios, as given by 

 Clarke, are as follows: 



100 NaCl An - /r> , 



= 40.867 (Ramsay and Aston) 



AgCl 

 100 NaCl 

 AgCl 



= 40.7797 (Richards and Wells) 



10 Sodium chloride is particularly prone to retain traces of water or mother liquor 

 when crystallized from water solution. It seems safe to say that sodium chloride, 

 prepared in this manner, that does not slightly decrepitate just before fusion 

 is yet to be made. In their work upon the atomic weight of columbium (J. Am. 

 Chem.Soc. 37, 1783 (1915)) the writers found that sodium chloride dried at about 

 400 was not free from water. In some cases it retained over 0.1 percent, of 

 moisture which was not given off until the salt was fused. (This statement, 

 although not recorded in the paper just mentioned, is borne out by original 

 notes.) 



