774 



SCIENCE 



[N. S. Vol. XXVII. No. ( 



pendent on the law of maximimi work and 

 should lead to the recognition of what may- 

 be called the driving force of the actions — 

 I have not time to discuss it here. In our 

 experience there was only one notable ex- 

 ception to the rule: years ago we found 

 that urea esters would not react with 

 amines to give guanidines, a reaction which 

 would correspond entirely to the formation 

 of amidines from imido esters : 



NHjC ( NH ) OCH3 + NH3 -» 



NH,C ( NH ) NHj + CH3OH. 



And, yet, the guanidines are much stronger 

 bases than are the urea esters. Now it 

 happened that in our older work we had 

 almost invariably used the free esters and 

 amines, no salts. In a reinvestigation of 

 the action from the new point of view, 

 hydrochloric acid was added to help the 

 ionization of the urea ester. With this 

 simple modification, the method works 

 beautifully, excellent yields of guanidines 

 are obtained and the action falls into line 

 with the others. Quantitative measure- 

 ments showed too that the reaction pro- 

 ceeds with a velocity proportionate to the 

 concentration of the positive urea ester ion. 

 The result was interesting not only because 

 it represents a successful synthesis pre- 

 dicted by the theory, but also because in 

 this case the stronger base is the urea ester 

 and it takes the major part of the cat- 

 alyzing acid — for the imido esters and 

 ammonia the conditions were reversed. 

 And so the theory is found to work, 

 whether the reacting positive ions are pres- 

 ent in very minute or in larger masses, 

 whether the catalyzer combines in minimal 

 or in larger proportion with the substance 

 undergoing catalysis! 



We thus find that it is possible by 

 physico-chemical methods to determine the 

 mode of action of reagents, so-called cat- 

 alyzers, which we add to mixtures in or- 



ganic chemistry to make the actions "go." 

 By entirely analogous methods and prop- 

 erly chosen conditions the active component 

 may be ascertained by velocity determina- 

 tions in a large variety of organic reactions, 

 methods which are applicable not only in 

 chemistry proper, but also particularly in 

 the domain of biochemistry, where catalytic 

 action by acids, alkalies and enzymes is 

 of foremost importance. 



In conclusion, I should like to call atten- 

 tion to one other important method of 

 physical chemistry which has been exten- 

 sively applied in inorganic fields and is 

 now being used in organic work with- the 

 largest promise of valuable results. It is 

 the method of studying chemical reactions 

 with the aid of potential differences pro- 

 duced by a logical arrangement of reacting 

 substances— a method which Ostwald seems 

 to have originated and which he has devel- 

 oped into a chemometric method. One of 

 the most valuable applications is in the 

 study of oxidation and reduction, and it 

 was, in fact, first used by Ostwald in such 

 reactions in an investigation carried out 

 with Bancroft. Such potential differences, 

 according to the theory of Nernst, amply 

 confirmed by experience, are a function, in 

 the first place, of characteristic constants of 

 the reacting substances and, in the second 

 place, also, of the concentrations of the re- 

 acting substances, the ions, around the elec- 

 trodes. The application to an organic 

 problem will become clear by the considera- 

 tion of a specific case. We remember that 

 the oxidation of a great many organic com- 

 pounds like aldehydes and sugars is most 

 vigorous in alkaline solutions. "We use 

 ammoniacal silver solution and even sodium' 

 hydroxide with it as a most delicate test 

 for such aldehydes, and alkaline Pehling 

 solution for sugars. Is the alkali necessary 

 to liberate silver oxide or copper oxide as 

 the true oxidizing agent, as is often sup- 



