152 



Z. C. Jones — Estimation of Boric Acid. 



silicondioxide is liberated by the excess of hydrochloric 

 acid, and this oxide, whether in hydrous or anhydrous condi- 

 tion, neither affects the indication with iodine nor phenol- 

 phthalein, nor does it form with mannite a compound of 

 acidic properties. Ammonium salts interfere with the indi- 

 cation given by phenol phthalein and may be removed by boil- 

 ing with potassium hydroxide in excess, or an indicator used 

 not affected by them. 



To test the action of .fluorides in the process, several experi- 



ments were made in which hydrofluoric acid (10 cm3 of — 



solution) was introduced into the solution containing salts of 

 sodium, free hydrochloric and boric acids. Barium chloride 

 w T as then added and the analysis for boric acid completed in 

 the usual way without the accuracy of the results being in any 

 way interfered with by the presence of hydrofluoric acid. 



The following table contains the results of a series of anal- 

 yses in which the boric acid was first drawn into an excess of 

 sodium hydroxide, then estimated according to the method 

 described. 



The standard solutions of boric acid used contained I, 7'153 

 grin, and II, 7706 grm. per liter. The solution of free sodium 

 hvdroxide was 0*21427 normal. 



Table I. 





B 2 3 Sol. 



NaOH Sol. 



B 2 3 



B 2 3 



Errors on 





taken. 



required. 



taken. 



found. 



B 2 3 . 





cm 3 



cm 3 



grm.. 



grm. 



grm. 



(0) 



21-95 



21-02 



0-1571 



0-1577 



+ 0006 



i(2) 



20*68 



19-65 



0-1479 



01474 



— 0-0005 



/(3) 



20-73 



19-63 



0-1483 



0-1473 



-o-ooio 



f(4) 



23-05 



23-71 



0-1776 



0-1777 



+ 0-0001 



1 (*) 



23-10 



23-80 



0-1780 



0-1783 



+ 0-0003 



J (6) 

 1 (?) 



22-76 



23*35 



0-1754 



01750 



-0-0004 



24-08 



24-78 



0-1855 



0-1857 



+ 0-0002 



1 (8) 



22-00 



22-50 



0-1695 



0-1686 



-0-0009 



1(9) 



20*78 



21-28 



0-1601 



0-1595 



-0-0006 



Practical tests of the method were made upon specimens of 

 crude calcium borate and colemanite.* 



The finely-ground minerals were dissolved in hydrochloric 

 acid and the analyses proceeded with as above described. 



* These specimens were kindly furnished by Dr. C. A. Crampton, of Washing- 

 ton, whom 1 desire to thank for this courtesy. 



