Oxidizers in the Hydrolysis of Starch and Dextrins. 389 



arsenite solution is titrated. Especially noticeable is the fine 

 blue color, with only a tinge of purple twice. The same thing 

 is noticeable in the next series, by which it is seen that no 

 reasonable excess of acid potassium carbonate causes any loss. 









Table IX. 











No extra dilution. 





n/10 











As 2 3 . 



n/10 I sol. 



KHC0 3 



. Starch solution. Color. 





cm 3 . 



cm 3 . 



cm 3 . 



cm 3 , ordinary pure potato. 





10 



9'82 



5 



1*5 deep blue 





10 



9*82 



10 



" deep blue 





10 



9-83 



15 



" deep blue 





10 



9-82 



20 



" deep blue, 



purplish 



10 



9'8L 



25 



" deep blue 





As still further corroborative proof a solution of tartar 

 emetic was made up as follows.* Tartar emetic was recrystal- 

 lized, dried by exposure to the air and pulverized ; 16 grm. 

 were weighed out and dissolved in 200-300 cm3 of water ; 20 

 grm. of tartaric acid, dissolved in a little water and filtered, 

 were added and also l cm of strong hydrochloric acid. The 

 solution was diluted to one liter. The significant fact about 

 the following titrations is the absence of any red colors, such 

 as are historically connected with antimony titrations. Indeed, 

 Freseniusf speaks of the red as giving the closer reading. 









Table X. 







n/10 Tartar 











Volume. 



emetic. 



n/10 I sol. 



Starch sol 



KHCO3. Color. 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



pure potato 



cm 3 . 



100 



10 



9-58 



1-5 





10 blue, no red 



100 



10 



9-58 



1 5 





10 blue 



75 



10 



9-56 







10 yellow 

 25 blue, 



125 



50 



4775 



15 















(purplish tinge) 



125 



50 



47'75 







25 yellow 



The average of the 10 cm3 readings (absolute) multiplied by 

 five equals 47-73. The absolute 50 cm3 reading (47-75-0-02) 

 equals 47*73. Evidently even tartar emetic causes no loss on 

 pure starch, for the 50 cm3 reading agrees with the plain iodine 

 reading for the same amount and with the 10 cm3 titrations. 



The severest test of all was then made on the pure potato 

 starch solution. With it were tried the two oxidizing experi- 

 ments with hydrogen dioxide and potassium permanganate. 



I. Into an Erlenmeyer flask 100 cm3 of water, 10 cm3 of acid 

 potassium carbonate, 4 cm3 of the starch solution and 5 cm3 of 



*Gruener, this Journal, vol. xlvi, Sept., 1893. 

 \ Freseuiu^, Quant. Anal., 6 te Aufl., II, 818. 



