1919] 0/M 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM Z41 



into thin slices which were dropped into about 200 cc. of boiling 

 95 per cent alcohol containing 1 per cent of strong ammonia. 

 After boiling for 10 or 15 minutes, this material was transferred, 

 as nearly quantitatively as possible, to a Soxhlet extraction 

 apparatus and extracted for 18 to 24 hours. After washing 

 out the extraction apparatus with alcohol, this extract, which 

 usually amounted to 400-500 cc, was then evaporated in vacuo 

 at a temperature of 35-40° C, leaving finally a volume of 40- 

 50 cc. This extract always contained a certain amount of loose 



starch, which was removed by centrifuging, after which the 



extract was made up to 200 cc. with doubly distilled water. 

 When the analyses could not be made at once, 2 per cent toluol 



was added as a preservative. 



This method of extraction and evaporation in vacuo is essen- 

 tially that described by Davis, Daish, and Sawyer ('16) and is 

 quite effective in removing the sugars. The necessity for 

 transferring the material from one vessel to another several 

 times during the process introduces the possibility of error, 

 but with careful handling this is small. 



Estimation of reducing sugars.— In making the determinations 

 of reducing sugars, the method described by Shaffer ('14) was 

 employed, with slight modifications. Forty cc. of the sugar 

 solution were used instead of the 10 cc. recommended. This 

 was done on account of the dilution, which made duplicates 

 difficult to obtain when only 10 cc. were used. Five cc. of 

 water and 5 cc. of colloidal iron brought the total to 50 cc, 

 instead of 40 cc. as in the original method used by Shaffer. 

 After removing the iron by centrifuging and filtering, two 15-cc 

 samples of the filtrate were used for the determinations, each 

 sample corresponding to 12 cc. of the original si 

 The dissolved cuprous oxide was titrated with 

 permanganate, and duplicates checked within .1 or .2 cc. of 



permanganate. 



Determination of sucrose. — For the determination of sucrose, 

 the method used was the same up to the point where the two 

 15-cc samples were measured out. Then 1.5 gms. (10 per cent) 

 solid citric acid were added to each sample, as recommended by 



N 



mm 



Davis and Daish 



sample; 



