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- 
Hwibvyaatn els Ox varying from 0.85x10°°°. to O:98x10s'> 
expressed in terms of the conductivity of mercury at 0°C. 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 18°C. 
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. 
