SVANTE AERHENIUS WALKER 729 



equal increments of temperature the increase is not approximately 

 arithmetical, but geometrical. This circumstance indicates that the 

 increase in reaction velocity with temperature is not due to change in 

 physical properties of the reacting substances. A similar very rapid 

 change in reaction velocity is observed when ammonium salts are 

 added to ammonia which is saponifying ethyl acetate. Here the 

 explanation is that the ammonium salts greatly reduce the concentra- 

 tion of the free hydroxide ions which really determine the reaction. 

 May we not then surmise that in the inversion of cane sugar the 

 amount of the really active substances is increased by temperature? 

 The amount of hydrogen-ion, one of the active substances, is little 

 affected by temperature. We must, therefore, assume that the other 

 really active substance is not cane sugar, as this is not changed 

 in amount by temperature, but another hypothetical substance, 

 which is produced from cane sugar as fast as it is removed by 

 inversion. Arrhenius here reverts to his old distinction between 

 " active " and " inactive " molecules. The hypothetical substance is 

 " active cane sugar " formed from the inactive substance. It is pres- 

 ent at all available temperatures in very minute amount, and the 

 quantity of it in equilibrium with the inactive cane sugar increases 

 about 12 per cent per degree. We are therefore dealing principally 

 with the effect of temperature on an equilibrium, namely, that be- 

 tween the active and the inactive substance, and can apply van 't 

 Hoff's equilibrium equation d \o<^,k/dT=q/'2,T'\ where k is the equi- 

 librium constant and q is the heat of activation. For a small range 

 of temperature this leads to log k=G—A/RT, i. e., a straight line 

 should be obtained on Arrhenius's assumption if we plot the logarithm 

 of the velocity coefficient against the reciprocal of the absolute tem- 

 perature, the slope of the line measuring the heat of activation. 

 Arrhenius's equation actually applies to many homogeneous and 

 heterogeneous reactions, and although there is much that is arbitrary 

 in its derivation, it is in its general character quite in accordance 

 with modern ideas. 



Returning once more to his personal fortunes, we find that after 

 1887 he was recognized abroad as one of the chief figures of physical 

 chemistry, but the death of Edlund in 1888 deprived him of his 

 stoutest champion at home, and greatly reduced his chances of ob- 

 taining suitable academic employment in Sweden. Abortive negoti- 

 ations to establish him in a chair of physics at Utrecht and of chem- 

 istry at Graz were succeeded by a definite call to the chair of chemistry 

 at Giessen in 1891. Arrhenius, however, notwithstanding the invidia 

 mter suos to which he had been subjected, was intensely patriotic and 

 declined the offer on the chance of being appointed chief of the 

 laboratory of physics in the Hogskola (University College) at Stock- 

 holm, a post which at this time had become vacant. Arrhenius was 



