528 Dr. E. F. Armstrong and Mr. E. J. Caldwell. [Apr. 5, 



each experiment. In order to determine the end value, a portion of 

 the solution was heated on the water bath during 2 hours, a period 

 which sufficed to effect complete hydrolysis without giving rise to any 

 marked secondary change such as always occurs on prolonged heating 

 at the temperatures at which the rate of change was studied. The 

 ratio between the rotatory power at complete change and the initial 

 value was found, as the mean of three accordant observations, to 

 be 1-285. 



The results of a complete series of observations are recorded in the 

 following table. It is to be noted that in calculating the constant 

 from the logarithmic equation, t is taken in minutes. To make the 

 results comparable with those of other workers, the velocity constant K 

 is expressed in terms of a gramme molecular proportion of acid per 

 litre ; this merely involves the multiplication of the constant deduced 

 from the results approximately by two. 



Table I. — 18 per cent. (0*5 gramme molecule) Milk Sugar, 0*5007 

 gramme molecule HC1. Temperature 60°-l. 







Per cent. 



10* a 



-r l"gio 



t a — x 



Time in hours. 



an. 



hvdrolysed. 







19°-55 



o-o 





5 



20-22 



12-04 



1-85 



9 



20-62 



19-2 



1 - 71 



15 



21-27 



30-8 



1-78 



20 



21-83 



40-9 



1-90 



25 



22-17 



47-0 



1-84 



30 



22-47 



52-4 



1-79 



40 



23-23 



66-0 



1-95 



62 



24-23 



84-0 



[2-14] 



87 



24-93 



96-5 



[2-81] 



134 



25-15 





184 



25-28 





Mean 1 ■ 83 



216 



25-56 







Complete change 



25-12 







K = 3-65. 



In a second series of experiments, the value deduced from the first 

 eight successive observations — during which about two-thirds of the 

 sugar had undergone change — was K = 3 -42. 



In the interests of space, as the quotation of long series of values 

 serves no useful purpose, in discussing our remaining observations it 

 will suffice, as a rule, to give the mean value of K obtained in the 

 manner described. It is, of course, to be understood that K is 

 derived from not less than six accordant readings taken at regular 

 intervals during a period of 30 — 40 hours. 



It will be seen that after about 40 hours, when hydrolysis is half 



