226 GOLD IN SCIENCE AND IN INDUSTRY. 



The phenomena of the solid state throw an interesting light on the 

 interplay of the two great forces, the primitive or blind cohesion 

 which holds undisputed sway at the absolute zero, and the repulsion 

 due to the molecular vibrations which is developed by heat. This 

 interplay we know continues through the states which succeed each 

 other as the temperature is raised, till a point is reached at which the 

 ]nolecular re])ulsions so far outweigh the cohesive force that the sub- 

 stance behaves like a perfect gas. The problems of molecular consti- 

 tution are more likely to be elucidated by a study of the successive 

 states between the absolute zero and the vaporizing temperature than 

 at the upper ranges where the gaseous state alone prevails. The sim- 

 plicity of the laws which govern the jDhysical behavior of a perfect 

 gas is very attractive, but we must not forget that this simplicity is 

 only possible because repulsion has so nearly overcome cohesion that 

 the latter may l)e practically ignored. The attractiveness of this sim- 

 plicity should not blind us to the fact that it is in the middle region, 

 where the ojjposing forces are more nearly equal, that the most inter- 

 esting and illuminating phenomena are likely to abound. The appli- 

 cation of the gas laws to the phenomena of solution and osmosis 

 appears to be one of those cases in which an attractive appearance of 

 simplicity in the apparent relations may prove very misleading. 



Before passing from the specially metallic qualities of gold I will 

 only remind j^ou of the important part it has played in the researches 

 on the diffusion of metals by the late Sir William Roberts- Austin, 

 and in those of Mr. Haycock and Mr. Neville on the freezing points of 

 solutions of gold in tin, which led to the recognition of the monatomic 

 nature of the molecules of metals. 



3IOLECULES IN SOLUTION. 



It has occurred to me that the practice of the cyanide process of 

 gold extraction presents us with several new and interesting aspects 

 of the problems of solution. As you are aware, the gold is first 

 obtained from the ore in the form of a very dilute solution of cyanide 

 of gold and potassium, from Avhich the metal has to be separated, 

 either by passing it through boxes filled with zinc shavings or by 

 electrolysis in large cells. 



The solution as it leaves the cyanide vats may contain gold equal to 

 100 grains or more per ton, and as it leaves the precipitating boxes it 

 may contain as little as 1 or 2 grains and as much as 20 grains. 

 In the treatment of slimes much larger volumes of solution have to be 

 dealt with, and in this case solutions containing 18 grains per ton 

 have been regularly passed through the precipitating boxes, their 

 gold content being reduced to 1^ grains per ton. In round numbers 

 we may say that 1 gram of gold is recovered from 1 cubic meter of 

 solution, while • 1 gram is left in the solution. Even from the point 



