GOLD IN SCIENCE AND IN INDUSTRY. 233 



In importing this mechanical view of the breaking down of com- 

 plex into simpler molecules we are not without some solid basis of 

 facts to go upon. My own observations have shown that even in the 

 solid state the crystalline molecule can be broken down by purely 

 mechanical means into the simpler units of the amorphous state; 

 and, further, that the Avater molecules of a crystal may by the same 

 agency be broken away from their combination with the salt mole- 

 cides. Since the publication of the earlier of these observations, 

 Professor Spring has shown that the acid sulphates of the alkali 

 metals may be mechanically decomposed into two portions, one of 

 which contains more acid and the other more base than the original 

 salt. It is important to recognize that in these three apparently 

 short steps the transition has been made from the overcoming of the 

 simple cohesion of similar molecules in contact with each other to the 

 breaking asunder of the chemical union of dissimilar molecules. At 

 each step the solid molecules appear, not as mere ethereal abstrac- 

 tions, but as substantial portions of matter which can be touched and 

 handled mechanically. 



The physical properties of a gas are primarily due to its being an 

 assemblage of rapidly moving molecules. These simpler and more 

 general i)roi)erties can coexist with, and may be modified by, the more 

 com])lex relations introduced by chemical affinity as it occurs in com- 

 pound gases and mixtures. 



It appears to me quite legitimate similarly to regard the physical 

 properties of a liquid as due to its being an assemblage of rapidly 

 moving molecules. The liquid system is highly condensed, and the 

 motions of its molecules are controlled by the cohesive as well as by 

 the repulsive forces. The closer approximation of the molecules 

 may reduce their mean free path to an extremely small amount, or it 

 may even cause their translatory motion to disappear, so that the 

 whole kinetic energy of the liquid molecules may be in the form of 

 rotation or vibration. 



As w^e can imagine a perfect gas, so also may w^e imagine a perfect 

 liquid, the physical properties of which are as simply related to the 

 laws of dynamics as are those of the gas. But the conditions of the 

 liquid state being also those most favorable to the play of chemical 

 affinity, the internal equilibrium of solutions or of mixed liquids 

 must be a resultant of this affinity, together with the primary forces 

 of the ideal liquid state. 



An ideally perfect solution — that is, a solution of the physical prop- 

 erties of which are determined solely by the number of molecules it 

 contains in a given volume — must consist of a solvent aiul a solute 

 Avhich have no chemical affinity for each other, so that their mole- 

 cules will neither associate nor dissociate in solution. Probably only 

 m 1905 19 



