SYSTEMS INTERMEDIATE 375 



due to the motion of this carrier, ammonia will be carried from the 

 dilute to the concentrated solution. If the vapor pressures of the two 

 solutions are known, we may calculate the work due to the transfer 

 of solvent by the negative carrier, the number of molecules of ammonia 

 associated with this carrier being assumed. The complete expression 

 for the electromotive force is: 



_ 2nRT . M* 



where m is the number of molecules of ammonia associated with the 

 negative carrier and p 2 and p v are the vapor pressures of the two solu- 

 tions. If we place n = in this equation, that is, if we assume that 

 all the current is carried by the negative carriers, we may calculate a 

 maximum value for m, if the electromotive force of the cell and the 

 vapor pressures of the solutions are known. For a concentration cell 

 between solutions whose concentrations were 1.014 and 0.627 normal, the 

 measured electromotive force was 0.08 X 10' 3 volts, and the ratio of the 

 vapor pressures was 1/1.006. This yields for m the value 0.67; that is, 

 a value less than unity. Since m cannot be less than unity, it follows 

 that at least a portion of the current must be carried by carriers not 

 associated with ammonia. It is evident, from the manner in which the 

 electromotive force and the vapor pressure of ammonia solutions vary 

 with the concentration, that at higher concentrations the value calculated 

 for m would be even smaller. The negative carriers in solution, there- 

 fore, consist of negative electrons surrounded with ammonia molecules. 

 As the concentration of the solution increases, the number of ammonia 

 molecules associated with the carriers decreases and ultimately a por- 

 tion of the carriers becomes entirely free from ammonia molecules. The 

 great increase in the relative carrying capacity of the negative carriers 

 at higher concentrations is due to the presence of these free negative 

 electrons. 



5. Conductance of Metal Solutions. If the increased carrying 

 capacity of the negative carrier is, in fact, due to an increase in the 

 mean speed of this carrier, the speed of the positive carrier remaining 

 substantially constant, then the equivalent conductance of solutions of 

 the metals in liquid ammonia should increase largely with the concentra- 

 tion at higher concentrations. Since the determinations of the molecular 

 weight, as well as the results on the motion of the boundary between a 

 metal and a metal amide solution, indicate that an equilibrium exists 

 between the positive ions and the negative carriers and the neutral 

 atoms, it is to be expected that the ionization of the metal will vary as a 



