162 Scientific Proceedings, Royal Dublin Societij. 



in the acid solution are different from those in a neutral solution. Barry 

 himself has shown that the heat of solution of sucrose in acid is different 

 from that in water. 



The Hydrolysis of Maltose. 



We also made some attempts to obtain a value for the thermal changes- 

 which take place when maltose is hydrolysed to dextrose under the influence- 

 of maltase. According to Stohmann and Langbein (2), the heat of combus- 

 tion of maltose hydrate is 1339-S cal. per gm. mol., and for two gm. mol. of 

 dextrose it is 1347'4. This would give a value of - 7'6 cal. per gm. mol. 

 for the hydrolysis of maltose, but such indirect determinations are of little- 

 use. 



The direct determination of this value is attended by many difficulties.- 

 At air temperature maltase acts very slowly, and even at the optimum, 

 temperature, about 38° C, the action is still rather slow. A 5 per cent, 

 solution of maltose when acted on overnight by one-twentieth of its volume of 

 extract of dried brewers' yeast at 38° 0. was only hydrolysed to tlie extent of 

 about 42 per cent. An attempt was made to obtain a value for the thermal 

 changes accompanying hydrolysis by filling the flasks with a 5 per cent, 

 solution of maltose at 38° C, and using an extract of dried yeast as a source of 

 maltase. A curve showing the change in the galvanometer deflections during 

 1-| hours was plotted, and then the capsules were ruptured. Any thermal 

 changes produced by the action of the enzyme on the maltose should cause a 

 change in the direction of the curve. No change was noted, but after I5 hours 

 the amount of hydrolysis, when determined by the polarimeter, was so small 

 as to be within the limits of experimental error, and so no conclusions could 

 be drawn. 



In order to obtain accurate results it would be necessary to obtain a 

 much more active preparation of maltase, and to have a pair of flasks so 

 carefully adjusted that, when filled with a sugar solution at 38= C, the 

 temperature of the two fell at exactly the same rate. This would ensure 

 that any change in the deflections of the galvanometer was entirely due to 

 the action of the enzyme. 



