SYSTEMS INTERMEDIATE 367 



common with those of metallic systems and, on the other hand, with 

 those of electrolytic systems. 1 These are solutions of the alkali metals 

 and the metals of the alkaline earth in liquid ammonia and organic 

 derivatives of ammonia. In order to make clear the bearing of these 

 solutions on the problem of metallic conduction, it will be necessary to 

 discuss in some detail the properties of these solutions of the metals in 

 liquid ammonia. 



2. Nature of the Solutions of the Metals in Ammonia. The alkali 

 metals are extremely soluble in liquid ammonia, yielding solutions whose 

 external appearance depends upon their concentration. Dilute solutions 

 of the alkali metals, as well as of metals of the alkaline earths, exhibit a 

 fine blue color, whose absorption for all wave lengths is relatively 

 great. 1 * At higher concentrations, the solutions possess a marked re- 

 flecting power for all wave lengths. Very concentrated solutions exhibit 

 distinct metallic reflection of a color intermediate between that of copper 

 and gold. Among the earlier investigators of these solutions there was 

 much discussion as to whether the metal exists in solution as such or as 

 a compound with the solvent. Cady 2 showed that these solutions are 

 excellent conductors of the electric current and that in concentrated 

 solutions the passage of the current is characterized by the absence of 

 polarization effects at the electrodes. Finally, it has been shown that, 

 in the case of the alkali metals, stable compounds between the metals 

 and the solvent cannot be separated from these solutions. 8 While com- 

 pounds between the metal and the solvent may exist in solution, such 

 compounds, if they exist, possess little stability as follows from the low 

 value of the energy changes accompanying the process of solution. In 

 the case of the metals of the alkaline earths, however, it has been shown 

 that compounds may be separated from solution, in which the metal is 

 combined with ammonia. Kraus has prepared the compound Ca(NH 3 ) 6 

 and recently Biltz 4 has prepared the compounds Ba(NH 3 ) 6 and 

 Sr(NH 3 ) 6 . These compounds possess a metallic appearance, resembling 

 that of the concentrated solutions of the metals in ammonia. 



Kraus has determined the vapor pressure of solutions of sodium in 

 liquid ammonia, from which he calculated the molecular weight of the 

 metal in these solutions. Since the molecular weight can be determined 

 only in dilute solutions, where the properties of the system are approach- 

 ing those of an ideal system, it follows that molecular weight determina- 



1 Kraus, J. Am. Chem. Soc. 9, 1557 (1907) ; ibid., SO, 653, 1157 and 1323 (1908) ; 

 iMd., S6, 864 (1914) ; ibid., 43, 749 (1921). 



la Gibson and Argo, J. Am. Chem. Soc. 40, 1327 (1918). 

 8 Cady, J. Phys. Chem. 1, 707 (1897). 

 Kraus, J. Am. Chem. Soc. SO, 653 (1908). 

 3iltz, Zfschr. f. Electroch. %6, 374 (1920), 



