150 Journal of the Mitchell Society [Jan. 



THE STABILITY OF KESII^ ACIDS AT SLIGHTLY 

 ELEVATED TEMPEEATUKES— A COKRECTIOK * 



BY CHAS. H. HEETY AND H. L. COX 



Schwalbe/ noting the evolution of carbon dioxide when 

 rosin was heated to 140° C. in air freed from carbon dioxide, 

 interpreted this result as the breaking down of the carboxyl 

 groups of the acids contained in the rosin. 



Herty and Dickson ^ showed that the carbon dioxide obtain- 

 ed by Schwalbe was due to one or more of the following factors : 

 traces of spirits of turpentine in the rosin, moisture, oxygen of 

 the air conducted through the heating flask and oxygen absorbed 

 by the rosin previous to the experiment. Rosin, prepared from 

 fresh oleoresin, freed completely from spirits of turpentine dur- 

 ing distillation, and heated in a current of dry nitrogen, showed 

 no signs of decomposition at 140°, even after seven hours' 

 heating at this temperature. 



But they further stated that if the resin acids were prepared 

 cold and freed from the other constituents of the fresh oleoresin, 

 such acids heated in dry nitrogen melted at 65°-Y0° C. and im- 

 mediately evolved carbon dioxide in quantity. No explanation 

 was offered of this seeming paradox, the results, however, in- 

 dicating a probable decomposition of some of the acid con- 

 stituents of the oleoresin during its separation by distillation, 

 in the woods, into rosin and spirits of turpentine. 



Later, in seeking an explanation, two possibilities suggested 

 themselves: First, that during the preparation of the acids 

 some oxygen might have been absorbed from the air, in spite 

 of the precautions taken; second, that the drying of the acids 

 in a desiccator over phosphorus pentoxide may have been im- 

 perfect. This last idea was suggested during the course of an- 

 other investigation in this laboratory, in which great diiSculty 

 was experienced in drying perfectly resin acids precipitated 



* Reprinted from the Journal of Industrial and Engineering Chemisty, Volume 

 6, No. 9, page 782. September, 1914. 



Presented at the 49th Meeting of the American Chemical Society, Cincinnati, 

 April 6-10, 1914. 



^ Zett. angew, Chem., 18, 1825. 



2 This Journal, 1, 68. 



