Bitter Pit and Sensitivity to Poisons. 237 



kept at 350 C. and tested at intervals with diops of iodine solu- 

 tion. With tlie 1 per cent, and tiie 0.2 per cent, solutions of tannie 

 acid a large coaguluni of starcli was formed condensing on stand- 

 ing. With 0.04: per cent, a slight coa<ruluni was formed, later 

 nearly dissolving. 



Tannic Acid. 3 Hours. 9 Hours. 20 Hours. 30 Ifoiu-s. 



5 c.c. of 1 %* - Strong blue. - Strong- blue. - Stronof l)lu<'. - Ppt. smaller 



but givin<:j 



strong blue. 



5 c.c. of 0.2% - Strong blue. - Strong blue. - Strong blue. - Ppt. smaller 



but giving 

 strong blue. 

 5 c.c. of 0.0-1% - Strong blue. - Fairly strong - Purple. - Pale purple. 



blue. 

 5 c.c. of 0.02% - Fairly strong - Fairly strong - Pale purple - Nil. 



blue. blue. 



5 c.c. of O.OOS% - Paler blue. - Greenish blue. - Nil. - Nil. 



5 c.c. of 0.001% - Grreenisli blue.- Greenish blue.- Nil. - Nil. 



5 c.c. of water - Greenish blue. - Purple. - Nil. - Nil. 



■ 'I'otal concentration one-tliird of this in eacii case. 



There are some indications that even after adding 5 c.c. of 0.2" 

 per cent, tannic acid (making a concentration of 0.07 per cent, 

 approximately in the whole liquid), a small amount of the preci- 

 pitated starch was converted into sugar at 35^ C., and there is 

 slightly less precipitation when the solutions are warmed to 38^ C. 

 before mixing them if they are mixed at 14^ or 15^ C. Accord- 

 ingly in the following experiment the solutions were all warmed 

 to 380 c. before mixing, and kept at that temperature for 2-i 

 hours. Each tube contained 5 c.c. of 1 per cent, starch, 5 c.c. 

 of 1 per cent, diastase, and 5 c.c. of tannic acid. The controls 

 were boiled. The tubes were shaken several times during the 24 

 hours, and then 10 c.c. of the supernatant liquid tested with 

 Fehling's solution, using an excess of sodium hydrate. The brown 

 precipitate dissolves, forming first a green, and then a brown 

 liquid, and tests showed that even in the presence of tannic acid 

 small quantities of sugar can be detected. Tannic acid itself gives- 

 a red precipitate^ with Fehling's solution, if the sodium hydrate ib 

 not in excess. If the latter is in excess the tannic acid reduction is 

 separated by a long interval from the sugar reduction, or is 

 practically arrested. The red precipitates were allowed to settle 

 for not more than 10 or 15 minutes, filtered rapidly on tared filter 

 papers, washed, dried and weighed, and the excess weight over the 

 control is given in the third column of the table. 



1. According to Sonnenscheiii, Ding. Polytechii. Jourii., Vol. cclvi., p. 555, 1885, 1 gram CuO = 

 0.4126 gram tannin and 0.4245 gram dextrose. 



