polariscopic readings, because the strong acid and the high temperature 

 employed (95 C.) make the rate of the mutarotation instantaneous 

 in comparison with the rate of the hydrolysis; but in the hydrolysis 

 by emulsin the polariscopic readings do not give the real extent of the 

 hydrolysis unless a considerable correction is made for the mutaro- 

 tation of the freshly liberated glucose. The case is very similar to 

 the hydrolysis of cane sugar by the enzym invertase, in which reaction 

 the mutarotation of glucose, as has been shown by one of the writers, 

 plays an important part. 



THE HEAL AND APPARENT COURSES OF THE HYDROLYSIS OF 

 SALICIN BY EMULSIN. 



The emulsin consisted of two samples, one from a chemical manu- 

 facturer, who stated that it had been prepared from almonds, and a 

 second, which we prepared by digesting powdered bitter almonds for 

 a day in water, filtering through cloth, precipitating a casein-like 

 substance with a little acetic acid, filtering, and precipitating the 

 emulsin with alcohol as a flocculent white mass. The salicin was 

 prepared by recrystallizing a kilogram of commercial salicin once 

 from alcohol and then twice from water. Five grams of this dry 

 product dissolved in 100 grams of water gave a solution of specific 

 gravity 1.013 at 90 C., and of -14.91 rotation in a 50 cm tube; 

 therefore the specific rotation of the pure salicin was 61.8; Noyes 

 and Hall 6 found -61. 5 to -62.2 and Tiemann c found -62.6. As 

 it was expected that salicin on hydrolysis by emulsin would liberate 

 /^-glucose, which would slowly change partially to a-glucose, means 

 were taken to stop the action of the emulsin at definite instants by 

 adding a little sodium carbonate; the slightly alkaline solution was 

 then read in the polariscope. Special experiments proved that the 

 action of the emulsin is stopped instantly by the sodium carbonate 

 and that the mutarotation of the glucose reaches completion almost 

 instantly in the alkaline solution; the rotations of these alkaline 

 solutions therefore show the real extent of the hydrolysis at the 

 time the alkali was added. In the experiment reported in Table I, 

 500 cc of an emulsin solution were mixed at the time with 20 

 grams of finely pow^dered salicin, the solution filtered after one min- 

 ute's shaking, and the filtrate kept at 30 C. in a thermostat. A 

 portion of it was used to fill a 50 cm jacketed observation tube, 

 which was also kept at 30. The readings of this portion, as shown 

 in column 2 of Table I and curve I of figure 1, give the apparent 

 course of the hydrolysis. It is this course which Henri measured. 



J. Amer. Chem. Soc., 1908, SO: 1160-1166, 1564-1583; 1909, 31: 655-664. 

 bLoc. cit. 



cBer., 1885,15:1600. 

 [Cir. 47 J 



