DISCUSSION OF EVIDENCE. 197 



simultaneously; but, as Reid has pointed out, in the presence of an 

 equal number of molecules of water and alcohol, the tendency of the 

 hydrogen ion to hydrate is greater than the tendency to form alcohol- 

 ates; and under these conditions the first reaction proceeds much more 

 rapidly than the second. 1 A very large number of types of reactions 

 could be discussed illustrating this same point, i. e., the value of the 

 solvate theory in interpreting chemical reactions. 



When we turn to physical chemical processes, the solvation of the 

 ions has to be taken into account at every turn. The velocities of the 

 ions are, of course, a function of the degree of their solvation; and the 

 behavior of the ions, both chemically and physically, is a function of 

 their velocities. The effect of dilution, and especially of temperature 

 on reaction velocities, is largely a question of the velocities of the ions 

 present, which, in turn, are a function of the degree of their solvation. 



In determining the actual concentration of a solution, the amount 

 of the solvent combined with the ions must be taken into account, as 

 has already been pointed out ; and without knowing the actual concen- 

 trations of solutions quantitative chemistry would be impossible. 



The solvate theory has thrown a flood of light on the whole subject 

 of the conductivity of solutions, or the power of the ions to carry the 

 electric current. It has shown us why the conductivity of lithium salts 

 is less than that of sodium and potassium, notwithstanding the fact 

 that the lithium ion is much smaller and lighter than the atom of sodium 

 or potassium. We now know that the lithium ion is much more 

 hydrated than the ions of these elements, and the mass of the moving 

 ion is really much greater in the case of lithium. 



When we come to the temperature coefficients of conductivity, the 

 solvate theory has enabled us to interpret results which, without its 

 aid, would be meaningless. We now know why ions with the greater 

 hyclrating power have the larger temperature coefficients of conduc- 

 tivity. We know why ions with the same hydrating power have 

 approximately the same temperature coefficients of conductivity, and 

 why dilute solutions have larger temperature coefficients of conduc- 

 tivity than concentrated solutions; 2 and, did space permit, we could 

 multiply examples, almost without limit, of the effect of the solvate 

 theory on physical or general chemistry. 



WHY IS THE NATURE OF SOLUTIONS OF SUCH VITAL IMPORTANCE NOT 

 ONLY FOR CHEMISTRY BUT FOR SCIENCE IN GENERAL? 



The fact is well recognized that modern physical or general chemistry 

 has reached out into nearly every branch of science, and has had an 

 important influence on many of them. The question arises: Why is 

 this the case? The answer is that physical or general chemistry is 

 primarily a science of solutions. 



1 Amer. Chem. Journ., 41, 509 (1909). Ibid., 35, 445 (1906). 



