278 REPORTS ON THE STATE OF SCIENCE. 



F. — Influence of Temperature on the Rate of Inversion. 



The velocity of inversion increases with rise in temperature. This 



fact was discovered by Wilhelmy, by Lowenthal and Lenssen and by 



Urech independently. 



1883 Urech gave an empirical equation to represent the influence of 



temperature, and at a later date showed how very great this effect 



1884. is by means of curves. 



1885 Spohr also deduced an equation for the influence of tempera- 



ture from his results. 



jgg^ This was criticised by Urech, who now made use of an expo- 



nential equation [which he showed to be the same as Van't Hoff's 



equation deduced theoretically for the alteration of the position of a 



chemical equilibrium with temperature]. 



1890 Hammerschmidt has also given an empirical equation to 



represent the influence of temperature on sugar inversion. 



1889 Arrhenius, too, adopted the Van't Hoff equation, viz. : — 



p<2=p<, £ 



X T.-T. Where 



2 ■ T, ..T, 



io<= velocity at temp. H.' 

 T=absolute temp. =(273 -f H '). 

 5'=thermal value of the change. 



He showed that it holds not only for the inversion of sugar but also for 

 a large number of other catalytic actions.' Now, seeing that Van't HoflF's 

 equation does not represent the effect of temperature on the velocity of 

 an action but on the position of an equilibrium, it must be conceded that 

 there is some kind of equilibrium to be disturbed in all these reactions. 

 Arrhenius supposes that only a certain proportion of the sugar is suscep- 

 tible to hydrolysis at any given moment. This is called the ' active part * 

 and the equilibrium is : — 



Inactive sugar '^ active sugar — q calories. 



No other explanation suffices to account for the great effect of a rise 

 in temperature, the increase in molecular velocity being only ^ per 

 cent., of ' ionisation ' of the acid -05 per cent, and of fluidity 2 per cent, 

 per degree rise in temperature. The hypothetical active sugar, which has 

 a calculated heat of formation of 25,600 cals., is supposed to be formed 

 by intramolecular change or by combination of the inactive sugar with 

 water. Additional non-electrolytes, neutral salts, and even the acid itself, 

 are supposed to increase the amount of 'active sugar.' 

 - q^Q Lippmann objected to this theory on the ground that it was 



impossible to imagine the nature of the active part, and he could 

 not understand why so much heat should be required for its formation. 

 This objection is certainly a serious one, as any internal rearrangement 

 of the molecule of cane sugar would involve a very small heat change ; 

 ,Qq- Brown and Pickering have shown that the heat of dissolution of 



cane sugar is only — 95 i cal, per equivalent and the heat of inver- 

 sion itself is but 4,560 calories. 

 ■■QQ, Euler, on the other hand, has interpreted Arrhenius's 'active 



part ' as meaning the sugar which is dissociated into ions of glucose 



' H. Ley (1899) has shown that this equation holds good up to 100° C. 



