AQUEOUS SOLUTIONS. ARCHIBALD. 293 



Purification of the Salts. 



The salts were obtained as chemically pure from Eimer and 

 Amend of New York. They were carefully re-crystallized three 

 times. After being thus treated, no impurities to any extent 

 could be detected. 



Purification of the Water. 



The water used was purified by the method described by 

 Hulett,* except that a block tin condenser was used instead of 

 a platinum one. Water, purified by this method, had a conduc- 

 tivity at 18C, varying from 0.85 X KT 10 to 0.98 xlO~ 10 , 

 expressed in terms of the conductivity of mercury at 0C. It 

 was kept in bottles which had been used for this purpose for 

 several years. It was neutral and left no residue on evaporation. 



Preparation and Analysis of Simple Solutions. 



The method adopted was to make up as concentrated a solu- 

 tion as it was desired to measure. This solution was carefully 

 analysed, and from it successive multiple dilutions were pre- 

 pared by adding water, all solutions being prepared at a tempe- 

 rature of 18C. 



A volume of fifty cubic centimetres of these solutions would 

 be introduced into the electrolytic cell, and successive dilutions 

 prepared from this in the cell itself, by withdrawal of a certain 

 volume, and addition of an equal volume of water. As a check 

 upon errors of dilution, after a portion had gone through a 

 number of dilutions, it was taken from the cell and carefully 

 analysed, and, if found necessary, the previous determinations 

 of the concentration were corrected from these results. 



The concentration of the solutions was determined by gravi- 

 metric analysis, the quantity of salt in solution being esti- 

 mated from the amount of Barium Sulphate precipitated by 

 Barium Chloride, when added in slight excess to a known 



* Journ. Phys. Chem., Vol. I, p. 91. 



