138 Studies on Solution. 



determined the freezing-points of the solutions of anhydride and water, 

 and compared them with the freezing-points of known concentrations 

 of acetic acid. Menschutkin and Vasilieff treat with aniline and water, 

 and determine the acidity after the reaction 



C 6 H 5 NH 2 + (CH 3 CO) 2 = C 6 H 5 NHCOCH 3 + CH 3 COOH 



has taken place. Treadwell recommends treatment with barium- 

 hydroxide solution and titration of the excess of the latter, while 

 Edwards and Orton convert the anhydride into acetanilid, the latter 

 into phenylacetylchloramine, and then determine the chloramine volu- 

 metrically. 



The method finally adopted to purify the acetic anhydride was that 

 of repeated distillation, using a 5-bulb distilling head and discarding the 

 first and last fractions. This gave an anhydride which distilled prac- 

 tically constant at 138 to 139. Specific gravity determinations, using 

 a 10 c.c. pycnometer, gave a mean value of 1.0852 at 15/4. The 

 acetic anhydride was further tested by titrating weighed samples both 

 directly and by the method advocated by Menschutkin and Vasilieff. 



PURIFICATION OF SALTS. 



Only the purest salts obtainable were used. They were usually 

 Kahlbaum preparations, although some of other well-known firms were 

 used. These salts were dissolved in conductivity water, filtered from 

 any foreign matter present, and then recrystallized one or more times. 



APPARATUS. 



Thermostats. The constant-temperature baths were of the improved 

 form designed by Davis 1 of this laboratory. The thermometers were 

 of the differential Beckmann type. They were compared with a 

 standard thermometer, which had been calibrated at the Bureau of 

 Standards. Flasks, pipettes, and burettes for measuring purposes were 

 all carefully calibrated by weight. All bottles used (varying in 

 content from 50 to 6.1 c.c.) and all measuring flasks were of Jena glass. 

 A special apparatus was used for the alkali solution, to protect it from 

 carbon dioxide and water vapor in the air. 



SOLUTIONS. 



The water used in the preparation of the solutions was purified by the 

 method of Jones and Mackay 2 as modified by Schmidt. 3 It had a con- 

 ductivity at no time greater than 2X10~ 6 . 



The aniline used to combine with the excess of acetic anhydride was 

 the purest obtainable. It was further distilled as many tunes as 

 necessary to remove all decomposition products. The slightly colored 

 product was then kept in a cupboard protected from light. 



Carnegie Inst. Wash. Pub. No. 210 (1914). 3 Ibid., 19, 90 (1*97). 



2 Amer. Chem. Journ., 17, 83 (1895). 



