Part I. 

 GENERAL OUTLINE OF THE INVESTIGATION. 



The investigation to be described in the following series of articles was 

 undertaken for the purpose of studying through a wide range of tempera- 

 ture, extending from 18 to the critical temperature and above, the elec- 

 trical conductivity of aqueous solutions and such other physical and chem- 

 ical properties of them as are related to it or can be determined through 

 measurements of it. Aside from its direct physical significance, it is well 

 known that the electrical conductivity of solutions is a property of funda- 

 mental importance in connection with the ionic theory ; for it gives the 

 simplest and most direct measure of the ionization of substances, upon 

 which their chemical behavior in solution depends. A full investigation of 

 this property at all temperatures would therefore furnish a comprehensive 

 knowledge of the chemical equilibrium of dissolved substances in water ; 

 and if supplemented by determinations of the solubility of solid salts, which 

 determinations can also be made by measuring the conductance of their 

 saturated solutions, a fairly complete basis for the development of the 

 chemistry of aqueous solutions of electrolytes would be obtained. 



A large number of such investigations had previously been carried out at 

 ordinary temperatures, especially at 0, 18, and 25, and a few of them had 

 been extended to somewhat higher temperatures ; yet even at 100, where 

 the results have much practical importance owing to the frequent use of 

 boiling solutions and owing to the fact that it is the limiting temper- 

 ature attainable in open vessels, few, if any, accurate data had been 

 obtained owing to the difficulties arising from evaporation and from con- 

 tamination when glass vessels are used. This temperature has therefore 

 been selected in this investigation as one of those at which each substance 

 will be studied. Above 100 only a few isolated conductivity measure- 

 ments have been published.* Yet the solubility of substances and their 

 chemical condition in solution at these higher temperatures is of much 

 importance, not only from the standpoint of physical and chemical science, 

 but also from that of chemical geology and the chemical technology of 

 reactions under pressure. 



Thus Sack (Wied. Ann., 43, 212-224, 1891) investigated the conductivity of 

 three copper sulphate solutions up to 120. Maltby (Z. phys. Chem., 18, 155. 

 1895) found that upon heating up to 237 the conductance of an aqueous potassium 

 chloride solution steadily diminished. Hagenbach (Drude's Ann., 5, 276-312. 

 1901) observed a maximum in the equivalent conductance of a 0.01 normal KC1 

 solution. In all of these experiments the conductivity cell was made of glass and 

 was necessarily very small; therefore, owing to the solubility of glass at these 

 temperatures and to the danger of polarization of the small electrodes used, the 

 results have little significance. 



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