The Dissociating Powers of Free and of Combined Waters. 123 



suited to each salt. The hydrated salts, being so soluble, were in most 

 cases not recrystallized, but dissolved in conductivity water, filtered, 

 and used as concentrated solutions. 



SOLUTIONS. 



Solutions for the first three salts in table 100 were made as follows. 

 Quantities of the isohydric solutions of the two chlorides were made. 

 The amount of added salt necessary for each concentration was weighed 

 upon a watch glass and introduced into a calibrated flask through a 

 short-stemmed funnel. The salt was dissolved by one of the isohydric 

 solutions and the flask placed in the bath regulated for 25 C. When 

 the solution had come to temperature it was diluted to the mark with 

 more of the isohydric solution. The process was now repeated, using 

 the same flask and the other isohydric solution. But it was found that 

 the volume change caused by the added salts was considerable. This 

 means that the solutions when made would be of the proper strength 

 for the added salt but weaker for the isohydric solutions. The results 

 are, however, still comparable, as the volume change in the two iso- 

 hydric solutions was found to be about the same. 



Solutions for the other three salts in table 100 were made in a dif- 

 ferent manner. Instead of using the stock isohydric solutions, they 

 were made up as needed. The amount of potassium chloride necessary 

 to make the isohydric solution molar was weighed into the flask. 

 The added salt, being a hydrated one, could not be weighed directly. 

 It was added in the form of a concentrated solution of known strength 

 from a small burette. The solutions were finally brought to the mark 

 with conductivity water. For a comparable solution the necessary 

 number of cubic centimeters of a concentrated calcium chloride solu- 

 tion of known strength to make the solution 0.6951 molar was used in 

 place of potassium chloride. In this way solutions were obtained 

 accurate with respect to the isohydric solutions but not with regard to 

 the added salt, because of the errors due to improper drainage of con- 

 centrated solutions in a burette of such small bore. 



It was finally decided to take the densities of the various concen- 

 trated solutions and to add these solutions by weight rather than by 

 volume. The densities were taken with a pycnometer. The solutions 

 were added to the weighed flasks (capacity 25 c.c.) from a burette with 

 a finely drawn tip. With care the solutions could be weighed to 

 within 1 or 2 mg., and this proved to be the most accurate method of 

 handling these salts. As before the same flask was used for comparable 

 solutions and the possibility of errors was thus, in part, avoided. 



The strengths of the different concentrated solutions of the chlorides 

 were determined by an estimation of the chlorine as silver chloride. 

 The other concentrated solutions were analyzed for the cations. All 

 solutions were made up at 25 C. 



