Mat 15, 1908] 



SCIENCE 



771 



has always been a subject for speculation 

 and investigation as to how and why a 

 catalytic agent like hydrochloric acid does 

 its work in actions like the saponification 

 of methyl acetate or the inversion of cane- 

 sugar or the digestion of food. Many 

 chemists have believed that more reactive 

 addition products are formed as inter- 

 mediate products; but of what nature 

 would they be to be more reactive? We 

 know that addition products, representing 

 more saturated compounds, very often are 

 really less reactive than the unsaturated 

 compounds from which they are obtained. 

 There are, however, important exceptions 

 to this rule: in trying to imagine just how 

 an acid can affect the speed of the action 



CH3COOCH3 + HOH + HCl -> 



CH3COOH + CH3OH + HCl 



we must recall the most fundamental fact 

 concerning acids, the fact that they have 

 the power to form salts with bases and 

 basic oxides. Here we have the acid and 

 the oxide and the idea is at once suggested 

 that salt formation of the ester with the 

 acid is the cause of the acceleration or 

 catalysis. Baeyer has shown, in fact, that 

 acid esters in common with other oxygen 

 compounds do form well-defined salts with 

 acids, oxonium salts, derived from quad- 

 rivalent oxygen, salts of exceedingly weak 

 bases, but still true salts, as shown by the 

 electrolytic experiments of Coehn. Now, 

 one of the most important differences be- 

 tween a very weak base and its salts is 

 that almost aU salts, no matter how weak 

 the base, ionize much more readily than 

 the weak base itself— this is a general 

 case when the addition product, the salt, is 

 more reactive than the unsaturated com- 

 pound, the base, and it is so through the 

 power of ionization.^ So it was thought 

 that the accelerating or catalytic action of 

 ^ Addition products often have a decomposition 

 tension producing an action as the result of an 

 increased potential of a component. 



the acid could be readily understood as due 

 to such salt formation, if the water reacts, 

 not with the ester itself, but only with its 

 positive ion, as expressed in: 



CH3CO.6.CH, -1- HOH -» CH3COOH + CH36H 



I I • 



H H 



The velocity of the reaction would then 

 be simply expressed in the fundamental 

 equation : 



dx 

 Velocity = ^ = •S'veiodty X Cone. p^,, lonsXConc. hoh- 



As a matter of fact, with this single as- 

 sumption that only the positive ions are 

 active, it is possible to deduce mathe- 

 matically by the rigorous application of our 

 simple laws of chemical equilibrium and 

 dynamics, as applied to the salts of very 

 weak bases, every fundamental fact that 

 has long been known about the processes 

 of saponification and esterification : In the 

 first place, by the application of these laws, 

 we find this equation resolving itself, 

 mathematically, into the equation : 



dx 

 Velocity = — =-ff''velocity X Cono. jj^ter X Cono. HOH 



X Conc.H i„„3_ 



the fundamental empirical equation which 

 tells us that at a given temperature the 

 velocity of saponification is proportional to 

 the concentrations of the ester, the water 

 and the hydrogen ions; the innumerable 

 measurements which have established the 

 correctness of this empirical equation agree, 

 therefore, obviously also with the funda- 

 mental equation of our theory. The latter 

 is also found to be in perfect agreement 

 with the two other characteristic features 

 of this catalysis— namely, that the ultimate 

 condition of equilibrium of the reversible 

 reaction of saponification and esterification 

 is not sensibly modified by the addition of 

 the acid, but is only reached more rapidly; 

 and finally, the catalyzing acid does not 

 appear to combine with any of the sub- 



