SYSTEMS INTERMEDIATE . 381 



expected, of course, that minor variations will be observed, since equiva- 

 lent solutions are not physically .identical. The densities of potassium 

 and sodium solutions, for example, differ; and the amount of ammonia 

 associated with the positive ions in these solutions doubtless differs. 

 Aside from minor differences, we should expect those properties of metal 

 solutions, which depend upon the negative carrier, to be relatively inde- 

 pendent of the nature of the metal. In Figure 67 are shown the conduc- 

 tance curves of dilute solutions of potassium, lithium, and mixtures of 

 sodium and potassium. The uppermost curve is that of potassium, the 

 lowest that of lithium, while the intermediate curve is that of a mixture 

 of sodium and potassium. The curve for mixtures of sodium and potas- 

 sium lies intermediate between that of sodium and of potassium. It is 

 seen that in the case of very dilute solutions of potassium and lithium, 

 the conductance values, as shown, lie below the true values owing to the 

 fact that these metals react with the solvent according to the equation: 



Me + NH 3 = MeNH 2 + H 2 ; 



that is, the metals react with the solvent to form the amides. This re- 

 moves a portion of the metal from solution and consequently the con- 

 ductance values measured are lower than the true values. From the 

 extensive data presented by Kraus,. however, there can be no doubt as 

 to the cause for the low values observed in dilute solutions in the case 

 of potassium and lithium. At intermediate concentrations, where the 

 formation of amide is not marked, the conductance of the solutions 

 diminishes in the order: potassium, sodium, lithium. At a given con- 

 centration, the difference in the values of the conductance of these 

 metals corresponds approximately to the difference in the conductance 

 of the positive ions of these metals. This shows that in dilute solutions 

 of potassium, sodium and lithium in liquid ammonia, the conductance of 

 the negative carrier is the same ; presumably, therefore, the negative car- 

 riers are identical in the three cases. At higher concentrations, where 

 the conductance of the positive ion becomes negligible in comparison 

 with that of the negative carrier, we should expect the specific conduc- 

 tance of the solutions to be practically the same at the same equivalent 

 concentration. As may be seen from Figure 66, the conductance curves 

 for sodium and potassium possess the same form, and over a considerable 

 range of concentration they are practically identical. 7 At higher con- 

 centrations, slight variations occur as might be expected, since the den- 

 sities of these solutions are not the same. The conclusion that the 



T Kraus and Lucasse, loc. tit. 



