90 Proceedings of Indiana Academy of Science 



2. In no case did the polyphenols or hydroxyacids give indication 

 of the formation of a complex suitable for an accurate volumetric deter- 

 mination of boric acid with sodium hydroxide. 



The polyphenols lowered the pH curve of boric acid to a consider- 

 able extent in the acid range but did not make the expected rise as 

 neutralization was approached and passed. A search of the literature" 

 reveals the fact that among the oxidation products resulting from the 

 exposure of alkaline pyrogallate to the air are carbon dioxide and acetic 

 acid. This fact would explain both the failure of the curve to make the 

 expected rise and the gradual decrease of the millivoltmeter readings 

 upon allowing the solution to stand in the air. A similar reaction may 

 be assumed in the ca.se of pyrocatechol. 



The aliphatic hydroxyacids all gave similar curves. Apparently 

 the two acids were neutralized separately just as if no complex had 

 been formed. If the assumption is made that no complex acid is formed, 

 it is merely a matter of the effect of the addition of a stronger acid to 

 the solution of a weaker one. Such a case is discussed by Lewis/ who 

 draws the conclusion that the degree of dissociation of the weaker 

 acid — boric — is directly proportional to its dissociation constant and 

 inversely proportional to the concentration of the stronger, glycolic for 

 instance. Application of this conclusion to the present problem makes 

 it obvious that as the amount of the glycolic acid is increased, the borate 

 ions become fewer and fewer, so that practically speaking, the presence 

 of the boric acid can be ignored during the titration of the glycolic. 

 Not until the latter is nearly all neutralized does the ionization of the 

 boric acid again need to be considered. During the latter part of the 

 neutralization the system differs from a solution of boric acid alone 

 only in that it contains in addition the salt of the organic acid neutralized 

 in the fir.st part of the process. The pH curve of the mixture then 

 shows a sharp upward break at the point of neutralization of the glycolic 

 acid, which break is much shorter than that for glycolic alone, how- 

 ever, since the boric acid is now ionizing and hydrogen ions are present. 

 Then follows a gradual rise with a small upward break representing 

 the neutralization of the boric acid. 



Both of the aromatic acids, upon approaching the end point of 

 the titrations, developed deep colorations, which would prevent any use 

 of thorn in ordinary volumetric analysis. Reference to the curves of 

 figure 3 shows that tannic acid is so inactive a substance that no con- 

 clusions regarding the nature of the complex formed can be drawn. 

 Gallic acid on the other hand did give evidence of the formation of a 

 complex capable of being titrated, but no application, other than electro- 

 metric, could be made of this fact, for the reason stated above. 



Summary. 



1. The fact that conductivity experiments indicate the formation 

 of a relatively highly ionized complex acid when certain polyhydroxy- 

 organic compounds are added to boric acid does not necessarily indicate 



® Meyer & Jacobson, "Lehrbuch dcr Organischen Chemie", 2, 423 (1902). 

 '"A System of Physical Chemistry", 1, 423 (1916). 



