148 L. C. Jones — Estimation of Boric Acid. 



None of the above methods with glycerine have, in raj 

 experience, given anything but comparatively crude results. 

 The weak acidic properties of boric acid, the interference (and 

 difficulty of removal) of carbondioxide with all organic indi- 

 cators sufficiently delicate to be used with boric acid, and 

 indeed, the procuring of a standard alkali containing no car- 

 bonate, together with the supposed detrimental influence of 

 silica and the lack of a convenient method for its removal, 

 have made the process of Gooch,* which involves distillation 

 and weighing with calcium oxide, the only means (though 

 requiring long time and exceeding care; in use for the accu- 

 rate separation and estimation of boric acid. Recently sodium 

 tungstate has been recommended from this laboratory f as a 

 substitute for calcium oxide to retain the distilled boric acid. 

 The entire process, however, is one of the most exacting in 

 analytical chemistry, and for this reason a convenient, rapid 

 and at the same time accurate method for the estimation of 

 boron is especially desirable. The iirst step toward the 

 development of such a process must be the convenient prepa- 

 ration and the accurate estimation of the standard solution of 

 alkali to be used for neutralizing the boric acid. This has 

 been found to be easily accomplished by the process recom- 

 mended by Kusler4 This observer, in an extensive investiga- 

 tion of the analytical methods for the volumetric estimation of 

 alkalic and alkali carbonates in solution, finds that both phenol- 

 phthalein and methylorange are appreciably sensitive to 

 carbonic acid, but when this interfering agent is removed by 

 precipitation with barium chloride according to the process of 

 Winkler,§ the remaining free alkali may be estimated with 

 great accuracy by phenol phthalein and decinormal hydrochloric 

 acid. 



Obviously, if the difficulties dependent upon the action of 

 carbon dioxide can be obviated, and if the acidity of the boric 

 acid can be increased to such an extent that a sufficiently sen- 

 sitive indicator will give with accuracy the neutralization 

 point with free alkali, and if the alkali and stronger acid can 

 be combined while boric acid alone remains free, then it 

 should be possible to estimate boric acid volumetrically. Ex- 

 periment has shown that barium chloride removes carbon 

 dioxide, and that mannite makes a combination with boric 

 acid strongly acidic to phenol phthalein. 



*Amer. Chem. Jour., ix, 23-33: Moissan, Comp. Rend., cxvi, 1087: Kraut, 

 Zeitschr. f. Aual. Chem., xxxvi, 165; Monte martini, Gaz. Chim. Ital., xxviii, l r 

 344. 



\ Gooch and Jones, this Journal, vii, 34. 



\ Zeitschr. f. Anorg. Chem , xiii, 124-150. 



§ Massanalyse. 



