232 GOLD IN SCIENCE AND IN INDUSTRY, 



This state of e(|uilibriii.ii is indicated on the diagram by marking 

 with a cross the mok'cnle ^vhich is exactly halfway through the 

 jjartition. 



At B a single solute molecule, S, has been introduced at the right 

 side. If this molecule exactly cancels tlie energy of on.e solute mole- 

 cule at its own end of the row, the equilibrium point will move one 

 molecule to the right, the solvent molecules will move in the same 

 direction, and one of their number will enter on the solution side. So 

 long as the row includes one, and only one, solute molecule, the 

 equilibrium will remain unchanged and no more solute molecules will 

 pass in. If another solute molecule arrives on the scene, the equilib- 

 rium will again be disturbed in the same way as before, and another 

 solvent molecule will pass into the solution. 



This mechanism accomplishes to some extent the work of a " Max- 

 well demon," in so far at least as it takes advantage of the movement 

 of rridiri(Ii/(d molecules to raise one part of a system at a uniform 

 temperature to a higher level or energy. 



A MECHANICAL VIEW OF DISSOCIATION IN DILUTE SOLUTIONS. 



The view that the phenomena of solution depend on the relative 

 kinetic energy of the solvent and solute molecules a})pears to aj)ply 

 with special force to the phenomena of dissociation in dilute solutions. 

 Under the gas theory there does not a2:)pear to be any reason why the 

 solute molecules should dissociate into their ions. So obvious is this 

 absence of any physical motive that Professor Armstrong has happily 

 referred to the dissociation as "" the suicide of the molecules." Others 

 have proposed to ascribe the phenomenon to what might be called " the 

 fickleness of the ions," thus supposing that the ions have an inherent 

 love of changing partners. These may be picturesque ways of label- 

 ing certain views of the situation, but the views themselves do not 

 appear to supply any clew to the physical nature of the phenomena. 

 With the acceptance of the view that the phenomena of solution are 

 largely due to the kinetic energy of the solvent molecules, the i)he- 

 nomena of dissociation also appear to take their place as a natural 

 result of this activity. For consider the situation of an isolated mole- 

 cule of cyanide of gold and potassium closely surrounded by and at 

 the mercy of some millions of water molecules all in a state of intense 

 activity. The rude mechanical jostling to Avhich the complex mole- 

 cule is subjected will naturally tend to break it up into simpler pov- 

 tions which are mechanically more stable. The mechanical analogy 

 of a ball mill in which the balls are self-driven at an enormous veloc- 

 ity is probably rather crude, I)ut it may at least help us to pictui'e 

 what, on the view now advanced, must be essentially a mechanical 

 operation. 



