Chemical Activity of Free and Semi-Combined Water. 137 



STATEMENT OF THE PROBLEM. 



The object of this investigation and the methods used were fully 

 outlined in the preliminary paper. However, in order that the com- 

 pleted work may be more readily understood, they are repeated here in 

 some detail. 



The studies on the absorption spectra of solutions carried out 

 in this laboratory by Anderson, Strong, Guy, Shaeffer, and others led 

 to the conclusion that a marked physical difference exists between free 

 and combined water. It seemed desirable, therefore, to determine 

 whether a similar chemical difference was to be found. With this in 

 view, Holmes and Jones 1 took up a study of the action of strongly hy- 

 drated salts and slightly hydrated salts on the hydrolysis of methyl 

 acetate and methyl formate. The method used consisted in measuring 

 the velocity of hydrolysis of the ester by pure water and by solutions 

 of slightly and strongly hydrated salts. The solutions were prepared 

 in such a way that the amount of water in each was the same and was 

 equal to the amount of pure water employed. Taking into account the 

 hydrolysis of the strongly hydrated salts, they found that these salts 

 hydrolyzed the ester much more rapidly than pure water itself. 



The reaction studied by Holmes and Jones was a very slow one and 

 indicated that combined water has greater activity than free water. 

 We wished to investigate the same problem, using a reaction that pro- 

 ceeded much more rapidly; therefore we chose the reaction involving 

 the conversion of acetic anhydride into acetic acid. 



EXPERIMENTAL. 

 PURIFICATION OF ACETIC ANHYDRIDE. 



Pure acetic anhydride was necessary for the work. The physical 

 properties as described in the literature vary greatly. The boiling- 

 points given range anywhere from 135 to 140 at 760 mm. pressure. 

 The densities given vary between 1.07 and 1.09. From this it can be 

 seen that it was impossible to test its purity by the ordinary simple 

 means. Acetic acid is the impurity most likely to be present in the 

 anhydride, and is very difficult to detect if only small amounts are 

 present. 0.51 gram of pure acetic anhydride, when completely hydro- 

 lized, is equivalent to 100 c.c. N/10 solution of sodium hydroxide, while 

 the same weight of a mixture containing 1 per cent of acetic acid is 

 equivalent to 99.85 c.c. This is within the experimental error. 



Methods of finding the actual percentage of acetic acid and anhydride 

 in a mixture have been given by Pickering, 2 Menschutkin and Vasilieff, 3 

 Treadwell, 4 Edwards and Orton, 5 and Orton and Jones. 6 Pickering 



a Carnegie Inst. Wash. Pub. No. 230 (1915). "Analytical Chemistry, 1914, vol. n. 



2 Journ. Chem. Soc. 63, 1000 (1893). Mourn. Chem. Soc. 99, 1181 (1911). 



Journ. Russ. Phys. Chem. Soc. 21, 190 (1889). *Ibid., 101, 1720 (1912). 



