222 VEGETABLE ENZYMES. XVIII 



a number of samples were hydrolyzed completely with dilute acid. 

 The results showed that for 15 cc. portions in which the blanks (orig- 

 inal reducing actions) gave 120 to 150 mg. of CU2O, reduction after 

 hydrolysis gave 220 to 250 mg. of CU2O. An excess of substrate 

 capable of forming reducing substances upon hydrolysis was there- 

 fore present. 



In general terms, the juice from winter potatoes showed greater 

 blanks and somewhat greater actions than the juice from new pota- 

 toes, and that from sprouted potatoes greater than that from winter 

 potatoes. These conclusions were confirmed by several experiments 

 with new potatoes which were ''aged" for from 1 to 2 weeks in a 

 warm room. The juice showed somewhat greater blanks and greater 

 actions after this "aging" of the potatoes. 



Doby2 had found by his method that sodium fluoride accelerated 

 the action of potato juice on added starch. In attempting to repeat 

 this work, by testing the residue, not merely the supernatant liquid, 

 with iodine, it was found that the action was not accelerated as he 

 stated. Further, by using the reduction method, it was found that 

 the action was retarded by the sodium fluoride at the indicated con- 

 centration (0.3 per cent). As pointed out before, the conclusions of 

 Doby were based upon incomplete observations. 



Discussion of Results. 



The results of Tables I and II may be summarized briefly. In 

 view of the greater number of experiments with new potatoes, the 

 conclusions will be based on the results with these, the other series 

 being used as confirmatory. 



With the juice alone, a large action was observed in the acid solu- 

 tion (pH 2), decreasing as the acidity decreased to pH 5, then increas- 

 ing again, showing a maximum at pH 6 to 7. The actions then 

 decreased with increasing alkaHnity, becoming at pH 9 to 10. 



The action of the juice on added soluble starch was marked at 

 pH 2, although less than on the juice constituents themselves. This 

 action decreased with decreasing acidity, giving a minimum at about 

 pH 4, increased again with a maximum at pH 6 to 7, and then 

 decreased to at pH 9 to 10. 



