BORON AND FLUORINE. 59 



tecting it from dust. The salt, stirred frequently, was thus 

 exposed for 12 days, by the end of which period the weight had 

 become practically constant. It was then assumed to have the 

 theoretical composition of the decahydrate. 



When carbon dioxide is passed through a solution of borax a 

 partial decomposition into sodium carbonate and boric acid takes 

 place; a solution thus treated will finally effervesce upon the 

 addition of an acid. It is only reasonable to suppose, therefore, 

 'that the moist borax crystals would also absorb some carbon 

 dioxide from the air. Such an absorption might take place, of 

 course, simultaneously with the evaporation of moisture, so that 

 the net result might still be a decrease in weight. In fact, it was 

 found that a sample of moist, powdered borax, entirely free from 

 carbonate, after being exposed to the laboratory air for several 

 weeks, gave a very slight effervescence with dilute hydrochloric 

 acid. The reaction was slight, but unmistakable. This action 

 of carbon dioxide on the moist crystals probably becomes inap- 

 preciable as soon as the borax is " air-dry." To what extent 

 carbon dioxide may have affected Rimbach's salt it is impossible 

 to say. The effect may have been negligible. Nevertheless the 

 fact remains that no steps were taken to eliminate this source of 

 error, however slight it may have been. The question is of much 

 interest for another reason. As borax, contaminated with traces 

 of carbonate, is said to effloresce more readily than the pure salt, any 

 absorption of carbon dioxide even might have been accompanied 

 by a slight loss of water of crystallization itself. 



While the influence of the factors just discussed is rather 

 uncertain, an error which may have affected the final titration 

 is much more tangible and must not be dismissed without com- 

 ment. In the titration of borax it is assumed that the boric acid 

 resulting from the reaction has no effect upon methyl orange. 

 This assumption, the writers believe, is not strictly correct, for 

 according to their experiments solutions of pure boric acid, par- 

 ticularly when fairly concentrated, are distinctly acid toward this 

 indicator, and it is only in every-day analytical work that this 

 factor may safely be neglected; not so, it would seem, in an 

 analysis of precision. Rimbach, it is true, did not neglect to 

 carefully consider this very point. He found, from a series of 

 experiments, that a solution containing 9 grams of pure ortho- 



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