REVISIONS OF THE THEORY OF ELECTROLYSIS. 159 



electrolysis I would not be understood to imply that we now have the 

 ultimate truth. Many cogent objections have been urged against the 

 theory of dissociation in its present form. Theories should be 

 regarded as helps or scaffolds only; they are necessary for the con- 

 struction of the edifice of truth, and they finally disappear like the 

 staging. We should use them as temporary expedients, not retaining 

 them till the whole edifice is completed, but only until a grand arch 

 is finished, some minaret or tower emerges against a clear sky or 

 light streams through some noble window. 



The i^hysicist or chemist, who is more intent to ascertain the truth 

 than to preserve consistency, holds to a theory no longer than he finds 

 it able to furuish supjDort. Faraday, the prince of research, said 

 that experimental work is a great disturber of preconceived theories. 



Just now the dissociation theory is in a state of siege, with many 

 A'aliant defenders. The objection is urged that there are many cases 

 of electrolytes in solution in which the osmotic pressure does not 

 exceed that required by the gas law. Hence, there can be no dis- 

 sociation. Also that the simplest cases of electrolysis are those of a 

 molten salt, such as silver electrodes in molten silver chloride. In 

 these cases there is no complication with a solvent and no dissocia- 

 tion by solution. In what way, then, is that migratory freedom of 

 the electrically charged part-molecules, which is assumed in the 

 theory of dissociation, secured in a molten salt? Doctor Kahlen- 

 berg has shown that " a normal solution of trichloracetic acid in 

 allyl mustard oil is a poorer conductor of electricity than the purest 

 water wdiich Kohlrausch ever prepared in contact with air, and 

 yet this solution attacks dry magnesium rapidly, and decomposes 

 dry carbonates of sodium and potassium." But chemical reactions 

 are assumed to depend on dissociation into ions, as does electrical 

 conductivity. 



This much is generally accepted: " The ions must be free to move; 

 but this migratory freedom may be secured either by ionic inter- 

 changes between the molecules, as Clausius imagined, or by a pro- 

 longed separation in accordance with the dissociation hypothesis of 

 Arrhenius and Planck. The essential point in the general ionic 

 theory is the migratory freedom." 



The solution of obscure problems, like those of electrol^^sis, in which 

 event the chief agent itself is an elusive enigma, is necessarily one 

 of prolonged effort, with many a flamboyant processional and the 

 not infrequent refrain of the later recessional. But there is no occa- 

 sion for discouragement, for we are destined to struggle forever with 

 the unsolved problems of the here and the hereafter. 



It is often darkest just before the dawn. Sometimes, too, we 

 emerge into the light with a suddenness that blinds before the eye 



