SYSTEMS INTERMEDIATE 373 



TABLE CXLIX. 



E.M.F. OF CONCENTRATION CELLS AND VALUES OF n AND FOB 



SOLUTIONS OF Na IN NH 3 . 



C a EX10 3 n 1 -^ 



0.870 0.080 0.00359 277.6 



0.732 0.328 0.0109 90,6 



0.335 0.620 0.0231 41.2 



0.164 0.72 0.0291 33.4 



0.081 0.86 0.0336 28.8 



0.040 1.07 0.0385 25.0 



0.020 1.38 0.0575 16.4 



0.010 1.80 0.0704 13.2 



0.005 2.60 0.0980 9.2 



0.0024 3.40 0.125 7.0 



In Figure 64 are shown values of the ratio ; in other words, the 



n 



ratio of the charge transported by the negative carrier to that transported 

 by the positive carrier. On examining the table, it will be seen that, for a 

 given concentration ratio, the electromotive force increases as the con- 

 centration decreases. At higher concentrations, the electromotive force 

 decreases very rapidly with increasing concentration and ultimately be- 

 comes extremely small. Referring to the figure, it is seen that at low 

 concentrations the ratio of the carrying capacities of the two ions ap- 

 proaches a limiting value; that of the negative carrier being approxi- 

 mately seven times that of the positive carrier. As the concentration 

 increases, the relative amount of current carried by the negative carrier 

 increases, at first slowly and then more and more rapidly. In the neigh- 

 borhood of normal concentration, the current carried by the negative 

 carrier is several hundred times as great as that carried by the positive 

 carrier. As we have seen, the positive carrier in a sodium solution is in 

 all likelihood identical with the positive ion of a sodium salt. As Frank- 

 lin and Cady have shown, the speed of this ion varies only little with 

 concentration. The increased carrying capacity of the negative ion at 

 higher concentrations must, then, be due to an increase in the mean 

 speed of the negative carriers. 



It is a noteworthy fact that the carrying capacity of the negative 

 carrier in dilute solutions is much greater than that of the sodium ion. 

 The speed of the negative carriers in these solutions must therefore be 

 much greater than that of the sodium ion. The speeds of the different 



