Conductivities of Some Unusual Salts. 159 



As a rule, salts in aqueous solutions are more dissociated at low 

 than at high temperatures. This is in accord with the Thompson- 

 Nernst hypothesis to which reference has already been made. Some 

 exceptions to this rule have been found by other investigators. Barium 

 nitrate, cadmium iodide, lead nitrate, and uranyl acetate have been 

 found to show an increase in dissociation at higher temperatures. 

 Shaeffer 1 has called special attention to the anomalous behavior of 

 tripotassium phosphate, and suggests as a cause abnormal exothermic 

 heat of dissociation. A great number of the substances studied in the 

 present investigation showed a slight decrease in dissociation with rise 

 in temperature. Sodium bromate, sodium thiosulphate, trisodium 

 phosphate, and lithium chromate showed a well-defined increase. 

 Several compounds have almost identical dissociations at all the tem- 

 peratures studied. 



TEMPERATURE COEFFICIENTS. 



It has been found that the increase in conductivity with rise in tem- 

 perature, is due primarily to the velocities with which the ions move. 

 This velocity is governed by the viscosity of the medium and the 

 volume and mass of the ion. It is well known that the general tendency 

 of rise in temperature is to decrease viscosity, and also the volume and 

 mass of the ion, if the ion is considered not as a charged atom or group 

 of atoms, but as a charged nucleus plus molecules of water, which must 

 be carried along in all migrations through the remainder of the solvent. 

 Jones has given a number of proofs for the validity of this conception of 

 ions. He has also shown that these complexes break down at higher 

 temperatures. With these facts in mind, we should expect a greater 

 increase in conductivity with rise in temperature in the case of strongly 

 hydrated salts than in the case of weakly hydrated substances. Taking 

 the amount of water with which a substance crystallizes as indicative 

 of the extent to which it is hydrated, it is found that all of the com- 

 pounds referred to in the above tables are in accord with this concep- 

 tion, except potassium ferricyanide and ammonium chromate. Ref- 

 erence has been made to the work of Jones and Getman and Jones and 

 Bassett, which throws some light on the dissociation of the complex 

 ferricyanide, and also shows that water of crystallization is not always 

 indicative of the degree of hydration to which a compound is subject. 

 While they proved that the ferricyanide is not hydrated, it is rather 

 probable that the lithium chromate is, since lithium salts, as a class, 

 have a much greater tendency to hydrate than the salts of sodium or 

 potassium. 



The temperature coefficients, expressed in percentage, decrease in each 

 case with rise in temperature. They increase somewhat on dilution. 

 This is especially noticeable with hydrated and hydrolyzed salts. 



. Chem. Journ., 49, 249 (1913). 



