L. C. Jones — Estimation of Boric Acid. 14' 



Art. XVI. — A Volumetric Method for the Estimation of 

 Boric Acid; by Louis Cleveland Jones. 



{Contributions from the Kent Chemical Laboratory of Yale University— LXXVIII.] 



When boric acid and mannite are mixed in solution, a 

 peculiar compound of strongly acid properties is the result. 

 This compound decomposes carbonates, and its acid taste 

 is comparable to that of citric acid, much stronger than that 

 of boric acid alone. Magnanini* has found that the pro- 

 duct of such a mixture of boric acid and mannite solutions 

 shows greater electrical conductivity and a lower freezing 

 point than a similar molecular solution of either substance 

 alone. Other polyatomic alcohols (but all to a less degree 

 than mannite) and some organic acids show this peculiar prop- 

 erty of combining chemically with boric acid to increase its 

 acid qualities.f Of this reaction between boric acid and the 

 polyatomic alcohols, Thomson,;}; Barthe,§ and Jorgensen|| have 

 taken advantage to develop methods for the volumetric esti- 

 mation of boric acid. Glycerine is used to form a combination 

 with boric acid, sufficiently acidic to give an acid reaction 

 when used with a sensitive indicator and make possible its 

 titration with an alkaline solution. Honig and Spitz^f show 

 that in the method of Jorgensen a very large amount of 

 glycerine must be used to prevent the appearance of the indi- 

 cation of alkalinity with phenolphthalein before all the boric 

 acid is neutralized according to the following equation : 

 2NaOH+B 2 3 =2NaOBO + H 2 0— ; that in the presence of 

 carbonates the solution must be boiled to decompose bicarbo- 

 nates and the escape of boric acid by volatilization prevented by 

 the use of a return condenser, and that silica must be removed 

 by the process of Berzelius, and the solution then neutralized 

 by the use of methylorange before a titration of the boric acid 

 can be made. 



Yadam,** for the estimation of boric acid in butter, makes 

 use of mannite, which, as he finds, gives sharper indication 

 with litmus than glycerine. According to this process, the 

 solution to be analyzed for boric acid is neutralized by the use 

 of litmus and a solution of sodium hydroxide. Mannite 

 (1-2 grm.) is then added, bringing about an acid reaction with 

 the boric acid present in free condition. The solution is then 

 titrated to alkalinity by sodium hydroxide. 



*Gaz. Chim., xx, 428-440, xxi, 134-145. 



\ Klein, J. Pharm. China., 4, vol. xxviii; Lambert, Comp. Rend., cviii, 1016-1017. 



X J. S. C. I., xv, 432. § J. Pharm. Chim., xxix, 163. 



|| Zeitschr. f. Angew. Chem., 1897, 5. 



^[Zeitschr. f. Angew. Chem. (1896), 549. 



**J. Pharm. Chim (6), viii, 109-111. 



