1904] 



Studies on Enzyme Action, 



5^7 



Since the above was written, a paper has appeared by Noyes and 

 others* on the hydrolysis of maltose and dextrin by dilute acids, which 

 in the main confirms Sigmond's results. The hydrolysis of starch by 

 dilute acids under pressure at temperatures about 100°, was studied in 

 detail by Eolfe and Defren in 1896.f 



Although the behaviour of cane sugar in any particular solution is 

 fairly in accordance with the law of mass action, marked departures 

 from the law are observed in contrasting the effects produced by 

 varying the concentration whether of sugar or of acid. Not only does 

 the value of K increase as the concentration of the hydrolyte is 

 increased ; it also increases beyond the proportionate value when the 

 concentration of the acid is increased. 



The outcome of the experiments described in the following pages is, 

 briefly stated, as follows : In the first place, it is shown that, within 

 certain limits, milk sugar is hydrolysed in accordance with the 

 logarithmic law ; but that in somewhat concentrated solutions there 

 is a marked tendency for " reversion " to take place, so that the course 

 of change in the later stages of hydrolysis departs from this law. 

 The rate at which milk sugar undergoes hydrolysis compared with 

 that at which cane sugar is affected is shown to be remarkably slow : 

 yet the effect of increasing the concentration is found to resemble 

 that produced by changes of concentration in the case of cane sugar 

 and maltose ; moreover, the products of change are found to exercise 

 an influence on the rate of change comparable with that exercised by 

 milk sugar itself. Finally, it is shown that an increase in temperature 

 has even more influence on the rate of change of milk sugar than on 

 that of cane sugar. 



Experimental Method. — The method adopted in determining the rate 

 of change was practically that used by previous workers ; but, as milk 

 sugar is hydrolysed very slowly at ordinary temperatures, the experi- 

 ments were carried out at 60° C. On account of the small change in 

 the specific rotatory power which milk-sugar solutions exhibit when 

 hydrolysed, it was necessary to work with strong solutions — the 

 solution most frequently used contained 18 per cent, of sugar, i.e., 

 0*5 gramme molecular proportion per litre ; this was hydrolysed by an 

 equivalent solution of chlorhydric acid. The solutions of acid and 

 sugar, heated to 60° and then mixed, and the mixture maintained at 

 60°. Portions were taken out at stated intervals of time : each sample 

 was quickly cooled and its optical rotatory power determined in 

 a 2 dcm. tube. As the heating was often extended over several 

 days, it was necessary to cover the solution in the flask with a layer 

 of molten paraffin. In order to make sure that no evaporation had 

 taken place, the solution was titrated with alkali at the end of 



* ' J. Am. Chem. Soc., J 1904, vol. 26 p. 266. 

 f ' J. Am. Chern. Soc, vol. 18, p. 869, 



