BORON AND FLUORINE. 61 



affect the end-point. Furthermore, these experiments prove that 

 boric acid does influence the end-point, inasmuch as the latter is 

 reached prematurely, that is to say, before it would be reached if 

 no boric acid were present. 



In order to fix the end-point with precision Rimbach, in the 

 final titrations, proceeded as follows: Standard hydrochloric 

 acid (about ^) was added to the borax solution until a faint 

 acidity was indicated. A more dilute acid (about ) was then 

 added to a blank until the tint was exactly equal to that of the 

 former solution. The more dilute acid thus required expressed 

 in terms of the original standard was subtracted from the acid 

 added to the borax solution and the difference was taken to 

 represent the hydrochloric acid actually needed to react with the 

 borax. It is evident that this mode of procedure did not correct 

 for any possible acidity of the boric acid itself; and if our observa- 

 tions in regard to the acidity of this acid be correct, it is also 

 certain that the approach of the end-point was thus hastened 

 somewhat and that, therefore, the amount of hydrochloric acid 

 recorded was slightly insufficient. 



Obviously we are now in a position to apply a correction to 

 Rimbach's results. But as the concentration of the borax solu- 

 tions used by him and, hence, that of the boric acid solution 

 formed, can only be reproduced approximately, such a correction 

 for the acidity of boric acid can not be rigidly applied. Further- 

 more, the standard of the acid used by the writers to measure this 

 acidity was not determined with the idea of actually revising 

 Rimbach 's results on this basis. Nevertheless it may be of interest 

 to see how and to what extent such a correction would have influ- 

 enced Rlmbach's value for boron. If, from the above data, we 

 calculate the value of this correction for the mean quantity of 

 borax titrated by Rimbach, the atomic weight of boron would be 

 lowered from 10.917 to 10.887. It is thus seen that a slight inac- 

 curacy in the method, an inaccuracy which would not be notice- 

 able in ordinary analytical work, 14 would affect the atomic weight 

 of boron to the extent of nearly 0.3 per cent, of its approximate 

 value ! 



14 In the titration of 1 gram of crystallized borax this error due to the acidity of boric 

 acid would be equivalent to less than 0.02 c.c. of JQ hydrochloric acid, an entirely 

 negligible amount. 



