418 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



The behavior of physical, that is to say molecular phenomena rather 

 than atomic, which are affected by temperature, is quite different. 

 The effect of temperature is in these phenomena quantitatively much 

 less than it is in phenomena which arise from chemical transforma- 

 tions. Thus the Viscosity of a liquid is diminished by an elevation of 

 temperature, it is true, but the reduction of viscosity which is brought 

 about by a rise of ten degrees in temperature does not exceed about 

 twenty per cent., so that the ratio: 



Viscosity at T +.10 



Viscosity at T 



is 1.2 or thereabouts. Consequently all the physical phenomena in 

 solutions which are dependent upon the viscosity of the solvent, such as 

 electrical Conductivity, and Diffusion are affected in a similar degree 

 by elevation of temperature. Those phenomena of which the rate is 

 determined by changes of Surface-tension have, in fact, a temperature- 

 coefficient of less than unity, the velocity of changes in capillary 

 tension being actually reduced by elevation of temperature. 



One consequence of this decided quantitative difference between 

 the effects of temperature upon chemical and physical phenomena is 

 that we may, with a fair degree of confidence, employ the temperature- 

 coefficient of a complex phenomenon which involves physical as well as 

 chemical changes as a means of gauging the extent to which the velocity 

 of the process is governed by the chemical transformations which it 

 involves. If the pace is set by the rate at which some chemical change 

 transpires, then the rapidity of the process will be at least doubled 

 and not improbably more than doubled by a rise of ten degrees in 

 temperature. But if the chemical transformations are subordinate to 

 some physical process and must await its development before they can 

 proceed, or if they are simply consequent upon physical changes such 

 as electrolysis, or alterations in surface-tension, then the pace of the 

 whole process will be set by this physical event and the temperature- 

 coefficient of the process may be expected to be less than 2 or even very 

 considerably less than 2. 



We have already seen that the various enzymatic hydrolyses which 

 occur in the digestion of the foodstuffs yield temperature-coefficients 

 which lie between 2 and 4; all of them exceeding 2 at temperatures 

 which are not too far above the temperature of the warm-blooded 

 animals. The temperature-coefficient of enzymatic processes neces- 

 sarily declines very rapidly at temperatures which are much in excess 

 of 40, because at these temperatures the acceleration of the auto- 

 destruction of the Enzyme itself is so great that its loss of activity more 

 than compensates for the gain in the velocity of the hydrolysis which 

 the residual undestroyed enzyme is able to bring about. We have, in 

 fact, to deal with the resultant of two opposed processes both of which 

 are accelerated by elevation of temperature. At lower temperatures 



