L. C. Jones — Estimation of Boric Acid. 149 



To obtain the boric acid alone in free condition many 

 attempts have been made. Gladding,* Thaddeefff and Kosen- 

 oladt;): have isolated the boric acid by distillation with methyl- 

 alcohol and a non-volatile acid. Many indicators theoretically 

 insensible to free boric acid have been used to indicate the 

 neutralization of the stronger acids. Hdnig and Spitz, § and 

 Thomson,! use methylorange, Morse and Burton,T[ tropaeolin 

 00, while Yadam** makes use of litmus. All these indica- 

 tors, however, have been found by experiment to be more or 

 less affected by boric acid in solution. On the other hand, I 

 have found in the well-known reaction according to which a 

 stronger acid liberates regularly iodine from a mixture of 

 iodide and iodate, the solution of this difficulty. If both the 

 iodide and iodate are in excess of the acid the entire amount 

 of free acid will be neutralized and the corresponding amount 

 of iodine liberated according to the following equation : 



5KI + KI03 + 6HCl=6KCl + 3H 2 + 3l a . 



This liberated iodine may be removed by sodium thiosulphate 

 and a solution obtained which is absolutely neutral containing 

 only neutral salts, potassium iodide, iodate and tetrathionate. 

 The statements made by P. Georgevicff and Furry,^ that boric 

 acid present in moderate amount in solution has not the 

 slightest action on a mixture of iodide and iodate, have been 

 experimentally verified. Therefore when this acid is liberated 

 by an excess of a stronger acid, and the iodine set free de- 

 stroyed by thiosulphate, it remains free in solution to be titra- 

 ted in any convenient manner possible. 



Following along the lines suggested by the above reac- 

 tions, a volumetric process for the estimation of boric acid 

 has been developed. For a basis of the investigations, a 

 standard solution of boric acid was prepared by dissolving 

 in a liter of water about eight grm. of carefully weighed 

 anhydrous boric oxide. This anhydrous boric oxide was pre- 

 pared from the several times recrystallized hydrous boric 

 acid by long-continued fusion over a blast lamp. A solution 



of approximately - sodium hydroxide was prepared from the 

 o 



ordinary sodium hydroxide of the laboratory. The free alkali 



* Jour. Am. Chem. Soc, iv, 568. 



\ Zeitschr. f Anal. Chem., xxxvi (9), 568. 



% Zeitschr. f. Anal. Chem, xxvi, 18. 



§ Zeitschr. f. Anorg. Chem. (18). 549. 



I J. S. C. L. xv, 432. 



«f[ Am. Chem. Jour., x, 154. 



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



\\ J. Prac. Chem., xxxviii, 118. 



XX Am. Chem. Jour . vi, 341. 



