( ^^-^ ) 



XIV. 



A DETKRMINATIO^f, BY MEANS OF A DIFFERENTIAL CALOEI- 

 METER, OF THE HEAT PRODUCED DURING- THE INVERSION 

 OF SUCROSE. 



By henry H. DIXON, Sc.D., F.R.S., 

 University Pi'ofesf3or of Botany in Trinity College, Dublin, 



AND 



NIGEL G. BALL.i B.A. 



[Read November 23 ; published December 14, 1920.] , 



Very little attention seems to have been paid to the heat changes 

 accompanying enzyme reactions. Theoretically these can be deduced from 

 the difference in the heats of combustion of the initial substances and 

 the products of the reaction; but, as Brown and Pickering (1) have pointed 

 out, such methods are inaccurate, as the amounts of the thermal changes 

 to be measured are so close to the limits of experimental error for the 

 combustion values. 



For example, in the case of inversion of sucrose, using the values for 

 the heats of combustion obtained by Stohmann and Langbein (2), we get^-'^''^<iii iris(/^7^ 



/• _.>^ 

 Sucrose .... 1352-7 cal. per gm. mol. 



Dextrose . . 673-7 1 _ ^g^^.g (^ - I^^H U 



Laevulose . . G75 9 



4', 



Difference S"! cal. per gm. mol. "^■■"^^£i££fiJi^-' 



From this it would appear that the heat of inversion of sucrose in the 

 solid state is + 3-1 cal. per gm. mol., or + 9-1 small calories per gram 

 inverted. This value represents only about 0-1 per cent, of the sum of 

 the quantities measured in order to determine it, and little reliance can 

 be placed upon its accuracy. In order to determine the heat of inversion 

 in the dissolved condition, this value must be corrected for the differences 

 in the heats of solution of the substances concerned, and, when this is done 



' Mr. Ball is indebted to the Department of Scientific and Industrial Research for a 

 maintenance grant which was received during the progress of this research. 



SCIENT, PROC. R.D.S., VOL. XVI., NO. XIV. Y 



