414 M. C. Lea — Color Relations of 



ions with which they were previously combined. That this is 

 true is shown by removing the hydrogen ions, which is easily 

 done by the addition of nitric acid. Thereupon those chlorine 

 ions which were previously influenced by, and influenced, the 

 hydrogen ions, now influence the ferrous ions, converting them 

 to ferric ions. 



The facts of osmosis seem to indicate that dissociated ions 

 are mechanically free, inasmuch as the total number of mole- 

 cules appears to be increased. But the above reaction, which is 

 one of a great number, shows that in a chemical sense they 

 cannot be considered as free. 



Those who, like Ostwald, on the contrary hold that dissoci- 

 ated ions are perfectly free* would perhaps explain the above 

 reaction by the asserted principle that plurivalent ions have a 

 tendency to lose a portion of their valency.f One of the 

 examples given (p. 796) is that of the trivalent iron ion, which 

 by reason of its tendency to lose valency, may act as an oxidiz- 

 ing agent. 



This reasoning does not seem to be sound. Whatever may 

 be the tendency of the ferric ion to lose valency, the tendency 

 of the ferrous ion to gain it is still stronger, so that ferrous 

 chloride acts as a powerful reducing agent by reason of the 

 strong tendency of the ferrous ion to acquire additional 

 valency. This tendency of the ferrous ion shows itself in 

 other ferrous salts and a similar tendency is exhibited by 

 cuprous and stannous salts. In fact it may be said that most 

 of our powerful reducing agents owe their activity to the ten- 

 dency of ions 'to acquire additional valency; consequently it 

 cannot be admitted that an opposite tendency prevails. And 

 when in the above mentioned reaction we find that ferrous 

 chloride in dilute solution with hydrochloric acid does not take 

 up additional chlorine ions actually present in spite of its 

 strong tendency that way, we are compelled to believe that the 

 chlorine ions of the hydrochloric acid, though mechanically dis- 

 sociated, are still held in check by, and hold in check, the 

 hydrogen ions. 



In this connection I may refer to some interesting remarks 

 made by Professor Fitzgerald in his recent Helmholtz Memo- 

 rial Lecture, reported in Nature (January 30, 1896). 



"It is almost impossible to explain dynamically the assump- 

 tion that free electrically-charged ions wander about in a 

 liquid in a condition at all rightly described as one of dissocia- 

 tion." 



And again : 



*Lehrbuch, 2d.Ger. ed., ii, 783. 

 fib., 796 and 801. 



