SCIENCE 



[N. S. Vol. XXX. No. 757 



ions are normal in behavior, we are led at 

 once to the principle of the constancy of 

 the solubility product, the substantial cor- 

 rectness of which has been demonstrated 

 by the experiments of Noyes, and the more 

 recent work of Stieglitz. An entirely sim- 

 ilar method which depended upon the elim- 

 ination of the undissociated electrolyte was 

 employed by Rothmund in his study of the 

 dissociation of picric acid. 



Another dedi;ction which is similarly 

 justified is that the product of the hydro- 

 gen and hydroxide ion concentrations is a 

 constant, in any dilute aqueous solution, 

 and this important constant has been ob- 

 tained by several independent methods, all 

 in excellent agreement. Finally the Nernst 

 equation for the electromotive force of a 

 concentration cell gives very satisfactory 

 results when we consider only the ion con- 

 centrations. If, however, we apply an 

 equation similarly obtained to the undisso- 

 ciated portion of the electrolyte we obtain 

 results which are by no means corroborated 

 by experiment. 



A few years ago I had occasion to make 

 a calculation which involved simultaneously 

 the application of all the principles which 

 I have just enumerated, the Nernst equa- 

 tion, the solubility product, the dissociation 

 constant of water. By the aid of these it 

 was possible to calculate from the decom- 

 position pressure of silver oxide the poten- 

 tial of the oxygen electrode. The potential 

 thus ol)tained differed more than one tenth 

 of a volt from the value previously ac- 

 cepted, but was in perfect agreement with 

 the results of the independent investiga- 

 tions published during the same year by 

 Haber and by Nernst. The calculation 

 would obviously have been vitiated if any 

 one of the principles used had been unre- 

 liable. 



To review the service rendered by these 

 simple generalizations deduced from the 

 ionic theory would be to summarize a very 



considerable part of the exact work in 

 physical chemistry published during the 

 past two decades. In the study of chem- 

 ical equilibrium and reaction velocity, espe- 

 cially in the process of rationalizing quan- 

 titative analysis, these principles are of 

 daily service. 



While therefore many difficult problems 

 relating to the application of the ionic 

 theory remain to be solved, this theory 

 must even at the present time be regarded 

 as established on a sound working basis. 

 Advance will come through the exact quan- 

 titative study of the properties of aqueous, 

 atid especially of non-aqueous, solutions. 

 After this work is completed it is not im- 

 probable that our views of the nature of 

 solutions will be greatly changed, but I 

 venture to predict that the later and better 

 theories will not be substitutes for, but 

 rather developments of, the simple hy- 

 pothesis of Arrhenius. 



Gilbert Newton Lewis 

 Massachusetts Institute 

 OF Technoloct 



TEE COLLEGES OF TEE UNITED STATES 



AND THE CAMPAIGN AGAINST 



TUBERCULOSIS ^ 



The colleges and universities of the 

 United States are social forces of such 

 power that the campaign against tubercu- 

 losis can not ignore them: it needs their 

 help, it seeks to enlist them among its 

 strongest allies. And the campaign is so 

 reasonable, so timely, and already so effi- 

 cient, that it may confidently expect the co- 

 operation of the colleges of the country, as, 

 indeed, it depends on the cooperation of all 

 intelligent men and women interested in 

 the betterment of man. 



First in importance among the aids 

 which the higher schools are giving is per- 

 haps the investigation of fundamental 



' Read before the International Congress on 

 Tuberculosis, Washington, D. C. 



