622 



SCIENCE 



[N. S. Vol. XXXIV. No. i 



deny rational progress towards the solution 

 of the innumerable and weighty problems 

 confronting us. 



Let me say in conclusion that it is my 

 firm belief that in the untrammeled con- 

 centrated study of the phenomena of dis- 

 ease, with the ward as the laboratory, will 

 medicine become truly scientific (in the 

 best sense of that word), therefore truly 

 rational, with hopes of conquest its best 

 endeavor and success its ultimate goal. 

 The change will evolve a man better taught, 

 better trained and possibly possessed of 

 better judgment. The numbers of those 

 who practise or pursue the "art" of medi- 

 cine will yet increase and reap larger and 

 more abundant rewards in satisfaction of 

 work well done than has hitherto been 

 dreamed of. For the new era will demand 

 the survival of the fittest to survive, and 

 the practise of the profession of medicine 

 will in even greater degree be counted the 

 most honorable of all professions. 



NOEMAN MacL. HaKEIS 



The Univeesitt op Chicago 



TBEOBIES OF SOLUTIONS^ 

 TwBNTT-ONE years ago the Chemistry 

 Section of the British Association at its 

 meeting in Leeds was the scene of a great 

 discussion on the nature of solutions. It 

 was my first experience of a British Asso- 

 ciation meeting, and I well remember the 

 stimulating effect of the lively discussion 

 on all who took part in it. To-day, speak- 

 ing from the honorable position of presi- 

 dent of the section, I conceive I can do no 

 better than indicate the position of the 

 question at the present time. And this ap- 

 pears to me the more appropriate as our 

 science has had this year to mourn the de- 

 parture of van't Hoff, the founder of the 



^Address of the president of the Chemical Sec- 

 tion of the British Association for the Advance- 

 ment of Science. Portsmouth, 1911. 



modern theory of solution, whose name will 

 remain one of the greatest in theoretical 

 chemistry — in time to come, it will, I think, 

 be considered almost the greatest. He had 

 expressed the hope that he might attend 

 this meeting as he did that twenty-one 

 years ago. The hope is not fulfilled: his 

 activity is merged in the final equilibrium 

 of death. But his ideas are part and par- 

 cel of the chemical equipment of every one 

 of us, and we know that whatever form the 

 fundamental conceptions of chemistry may 

 assume, the quantitative idea of osmotic 

 pressure will be to the theory of solution 

 what the quantitative idea of the atom is 

 to chemical composition and properties. 

 For I must emphasize the fact that chem- 

 istry is essentially a quantitative science, 

 and no chemical theory, no partial chemical 

 theory even, can be successful unless its 

 character is quantitative. To quote the 

 words of Lord Kelvin : 



I often say that when you can measure what you 

 are spealcing about, and express it in numbers, you 

 know something about it; but when you can not 

 measure it, when you can not express it in num- 

 bers, your knowledge is of a meager and unsatis- 

 factory kind; it may be the beginning of knowl- 

 edge, but you have scarcely in your thoughts ad- 

 vanced to the stage of science. 



A general theory of solutions must be 

 applicable to all solutions — to those in 

 which solvent and solute exist in practic- 

 ally mere intermixture, as well to those in 

 which solute and solvent are bound to- 

 gether in what we can not sharply distin- 

 iguish from ordinary chemical union. Be- 

 tween these extremes all grades of binding 

 between solvent and solute exist, and it 

 may be well to give a few examples illus- 

 trating the various types of solution. 



Where no affinity exists between solvent 

 and solute, the solution is practically of the 

 same type as a mixture of two gases which 

 are without chemical action on each other. 

 The solute is merely diluted by the solvent 



