368 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



tions are always more or less in doubt. However, if the molecular weights 

 are determined at a series of concentrations, it is possible to draw an 

 inference as to the limit approached, as the concentration of the solution 

 decreases, from the manner in which the apparent molecular weight 

 varies as a function of the concentration. In the following table are 

 given values of the apparent molecular weight of sodium dissolved in 

 liquid ammonia at different concentrations, and in Figure 63 are shown 

 these values plotted as ordinates against the logarithms of the concen- 

 trations as abscissas. 



TABLE CXLVIII. 



APPARENT MOLECULAR WEIGHT OF SODIUM IN AMMONIA AT 

 DIFFERENT CONCENTRATIONS. 



C Apparent Mol. Wt. C Apparent Mol. Wt. 



2.903 32.23 0.3665 25.31 



1.841 30.70 0.3587 25.27 



1.220 29.06 0.2669 23.53 



0.9910 28.80 0.2516 23.43 



0.9038 28.46 0.2261 23.41 



0.5614 26.39 0.1565 21.62 



0.5558 26.47 0.1519 21.58 



0.4104 25.36 



It will be seen that, as the concentration decreases, the calculated value 

 of the molecular weight decreases very nearly as a linear function of 

 the logarithm of the concentration over the ranges of concentration 

 investigated. It is not possible to state what value the molecular weight 

 approaches as a limit, but it is evident that the limit approached has a 

 value less than 23, the atomic weight of sodium. It appears, therefore, 

 that sodium dissolved in liquid ammonia exists in an atomic condition 

 and it is probable that the limit, which the molecular weight approaches, 

 has a value less than the atomic weight of sodium. This indicates the 

 presence of a molecular species other than the sodium atom in these 

 solutions. While similar molecular weight determinations have not been 

 carried out in solutions of metals other than sodium, nevertheless, in 

 view of the similarity of the properties of solutions of the different metals 

 in ammonia, it is highly probable that the state of these metals differs 

 little from that of sodium. 



3. Material Effects Accompanying the Current. The criterion for 

 determining whether a given substance is a metallic or an electrolytic 

 conductor is the absence or existence of material effects accompanying 

 the passage of the current. In dilute solutions of the metals in liquid 



