OF CERTAIN ORGANIC ACIDS IN AQUEOUS SOLUTIONS. 49 



The acids which had already been investigated by White and Jones 

 at the lower temperatures, and which were reinvestigated by the author 

 were, hippuric, gallic, picric, and crotonic. In every case very close 

 agreements were found, and the values at 35 agreed to within the 

 limits of experimental error. The temperatures were the same as those 

 used by the former investigators. 



REAGENTS. 



The water used was purified in the same manner as that employed 

 in the earlier investigations. This method was described in detail by 

 Jones and Mackay. 1 



The acids were obtained from Kahlbaum and Schuchardt. The 

 general method of purification was recrystallization from conductivity 

 water. The butyric acids normal and iso were purified by distilla- 

 tion in a vacuum ; acetaminobenzoic acid was recrystallized from ether. 2 

 Whenever possible the acids were carefully dried in a vacuum desiccator 

 containing sulphuric acid. If practicable, the melting-points of the 

 acids were taken as one criterion of purity. The "mother" solution, 

 i. e., the one with the greatest concentration, was made up whenever 

 possible by direct weighing, and then titrated against standard alkali. 

 The acids which are liquids were made up directly by titration. The 

 modification of this method for the higher temperatures was described 

 in detail in the paper by Wightman and Jones. 3 All flasks and burettes 

 used in this investigation were calibrated by the method of Morse and 

 Blalock, 4 and also by weight of the contained water. 



The sodium salts of the organic acids were used to determine the ju> 

 values of the acids, and were prepared by titration. It had been found 

 that the sodium salts of organic acids, in general, are completely disso- 

 ciated at a dilution of F = 2048. Therefore, a solution of the acid at 

 this dilution was just neutralized by sodium hydroxide, using phenol- 

 phthalein as the indicator, and its conductivity determined in the 



usual way. 



APPARATUS. 



The cells used in this investigation were the same as those employed 

 by Jones and Wightman. In their paper they state: 5 



"The cells resembled those used by Jones and Bingham, 6 with platinum- 

 plate electrodes attached to glass tubes containing mercury, the tubes being 

 sealed into ground glass stoppers. As many as eight cells were employed with 

 constants ranging from about 10 to 330 in Siemens units. A cell of special 

 type, 7 having a very low constant, was used for obtaining the conductivity of 

 the water. In order to get a sharp reading in the cells, the electrodes were 

 covered with a fine coating of platinum black, in the usual manner." 



iAmer. Chem. Journ., 19, 91 (1897). *Ibid., 46, 62 (1911). 



"Carnegie Inst. Wash. Pub. No. 170. *Ibid., 34, 493 (1905). 



3 Amer. Chem. Journ., 48, 320 (1912). Ubid., 45, 282 (1911). 

 *Ibid., 16, 479 (1894). 



