Chemical Activity of Free and Semi-Combined Water. 139 



The solutions of the non-hydrated salts were made up directly by 

 weight, while those of the hydrated salts were analyzed gravimetrically 

 and diluted to the required strengths. The chlorides of barium, 

 strontium, calcium, and magnesium were determined as silver chloride 

 and the sulphates of sodium and magnesium were determined as 

 barium sulphate. 



The solution of sodium hydroxide used in titrating the acetic acid 

 formed by the hydrolysis of the acetic anhydride was made up approx- 

 imately half-normal, using "sodium hydroxide from alcohol." It 

 was preserved in an apparatus protected from the impurities in the air. 

 It was standardized by titration against a solution of sulphuric acid of 

 about the same strength (0.4115 N). The sulphuric acid had been 

 standardized as barium sulphate. 



The indicator used was phenolphthalein, as it gives the best results 

 in titrating a weak acid with a strong alkali, the only objection being 

 that it is also sensitive to carbonic acid. Corallin had been tried, but 

 was not so satisfactory. 



METHOD OF PROCEDURE. 



The method in principle is a modification of that of Menschutkin 

 and Vasilieff, 1 and later employed by A. and L. Lumiere and Barbier. 2 

 In order that the results should be comparable, the amount of water 

 present must be kept constant ; therefore the specific gravity of the salt 

 solution was first taken, giving the weight of 1 c.c. From analysis, that 

 part of the weight due to the anhydrous salt alone was known for each 

 cubic centimenter. This known weight of salt, subtracted from the 

 weight of 1 c.c. of solution, gave the weight due to the pure water alone. 

 This, divided into the weight of 1 c.c. of pure water at that temperature, 

 gave the amount of solution in cubic centimenters equivalent to 1 c.c. 

 of pure water. The amount of solution thus calculated was pipetted 

 into a 250 c.c. Jena bottle. An equivalent of 100 c.c. of pure water 

 was taken in all determinations. The bottle was suspended in the 

 constant-temperature bath. There was also placed in the bath a 

 bottle containing the anhydride and a number of small empty bottles 

 of 50 c.c. capacity. 



When all had come to the temperature of the bath, the bottle was 

 removed and 5 c.c. of the anhydride introduced. Time was reckoned 

 from when the anhydride was first added. Solution took place 

 immediately on shaking, except in the case of the very concentrated 

 solutions. Aliquot portions were removed and placed in the small 

 50 c.c. bottles, the whole being kept in the bath. These small bottles 

 were removed, first every 5, then every 10 minutes, and a slight known 



Carnegie Inst. Wash. Pub. No. 60, 160 (1907). -Ibid., 130 (1910); 190 (1910). 



