164 SCIENTIFIC THOUGHT. 



attacked by chemists, became gradually better under- 

 stood and gained ground. The merit of having finally 

 introduced into our modern notions the idea of the free 

 mobility of the constituents of electrolytic compounds 

 41. belongs to W. Hittorf and F. Kohlrausch. The name 



Hittorfand i • i i • p • 



Kohlrausch. of the latter will be connected in the history or science 

 with the phenomenon of the " migration of the ions," 

 which he has expressed, after ten years of research 

 (1869-79), in his well-known law. The question was 

 put and answered, " What becomes of the energy of the 

 electric current ? " It was found that electrolytic conduc- 

 tion increased with dilution and temperature — two agents 

 which would favour dissociation. The phenomena of 

 dissociation had, moreover, been studied independently of 

 the galvanic current. Following in the track of Graham 

 and Andrews, a number of physicists abroad — notably 

 van der Waals, Eaoult, and Van't Hoff — had confirmed 

 and extended the view that bodies in solution resembled 

 gases, that the osmotic pressure of a liquid resembled 

 ordinary gas pressure, that the law of Avogadro regard- 

 ing the number of molecules in a gas could be trans- 

 ferred to matter in a state of solution, and that the 

 magnitude of the osmotic pressure in a liquid could be 

 used as a measure of the number of dissociated — wander- 

 ing — molecules which are contained in a given volume 

 of a solution, just as the pressure of a gas would increase 

 if the number of molecules in a given space were in- 

 creased through the splitting up of compounds. Apparent 

 anomalies in the behaviour of gases approaching conden- 

 sation were explained by the aggregation, and similar 

 ones in dilute solutions by the dissociation, of molecules. 



