Bitter Fit in Apples. 105 



2. — The Action of Tannic Acid on the iodine tent for dextrins 

 formed during diastatic action o?i starch. 



A final concentration of 1% tannic acid was found to have no 

 effect on this test, as used in Greenwood and Rothera's, and the 

 following experiments. This is because the conditions involve an 

 excess of iodine. The interference of tannic acid with the starch 

 and dextrin colours is due apparently to its forming' a combination 

 with the iodine, and naturally ceases when the iodine is in excess. 



3. — Action of Tannic Acid on the diastatic hi/droli/sfs of starch. 



Filtered starch solution was used throughotit the expei-iments, 

 which were done at a temperature of 38^ — 40^0. 



Experiment 1. (Tubes each contained 15 c.c. of mixture.) 



Using a 2.5% solution of taka diastase, which proved rapid in 

 action, the following mixtures were made up, and tested for com- 

 parative rates of action. 



Tannic Acid 

 (final concentration). 



.25% 

 .125% 



c and d were finished in about 5| minutes, and a about 2 

 minutes later. f> still gave a strong red-brown at the end of 20 

 minutes. 



Experiment 2. (Tubes each contained 10 c.c. of mixture.) 



This was done, using taka diastase, with weaker concoctions 

 of tannic acid than those used in Experiment 1. 



starch (1%). Diastase (2.5%). (fi„aT'concentrL«on). 



In 2 minutes, the control a .still gave a red-violet, whilst the 

 others were all red. b was finished in 5 minutes, c and d in about 

 8 minutes, and control a in 12 minutes. 



