Oxidizers in the Hydrolysis of Starch and Dextrins. 387 



lute readings were found by subtracting one drop from the 

 actual reading. To render the plain iodine readings sharp a 

 crystal of potassium iodide was added in the first two titra- 

 tions. 



Table YI. 









Yolume 125 cm3 . 









nJ10 

 ^s 2 3 . 



n/10 I sol. 



reading - 

 by iodine 



color. 



n/10 I sol. 

 reading 



by 



KI starch 

 blue. 



n/101 sol. 

 abs. amt. 



n/10 I sol 

 abs. amt. 



n/10 I sol. 

 abs. amt. 



calc'd 



from 



5 cm3 



n/10 I sol. 



abs. errors 

 in A, . . in B. 





A 



B 



A 



B 





A 



B 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



cm 3 . 



5 



1 drop* 

 4-94* 



1 drop 

 4-96 



4-92 



4-94 



4-94 



0-02 — 



o-oo± 



10 



9-88 



9-90 



9-86 



9-88 



9-88 



0-02 — 



o-oo± 



15 



14-83 



14-83 



14-81 



14-81 



14-82 



o-oi — 



o-oi — 



20 



19-78 



19-78 



19-76 



19-76 



19-76 



00± 



o-oo± 



30 



29-64 



29-64 



29-62 



29-62 



29-63 



o-oi — 



o-oi — 



40 



39-55 



39-55 



39-53 



39-53 



39-51 



0-02 + 



0-02 + 



50 



49-41 



49-41 



49-39 



49-39 



49-39 



o-oo± 



o-oo ± 



The most noticeable and important fact is that all loss, noted 

 in the beginning of this paper, has disappeared, and that the 

 plain iodine and the starch readings agree exactly except for the 

 first two titrations, and here there is only a difference of a 

 drop. The absolute errors are interesting as they show how the 

 absolute values fluctuate about a standard set by the 50 cm3 read- 

 ings. This fluctuation is limited to a drop plus or minus. 



The statement has been made that starch from different 

 sources has a varying power of absorbing iodine, e. g., that 

 potato starch absorbs three times as much as rice starch. f To 

 learn whether this fact had any bearing upon the question at 

 issue, and at the same time to learn whether pure starch solu- 

 tions made in the ordinary way (G. Gastine) would give as 

 delicate readings as when boiled with potassium iodide, solu- 

 tions were made from pure potato starch, pure rice starch, 

 pure arrow-root starch and a pure soluble, so-called, starch of 

 unknown origin. The results of titration with these solutions 

 as indicators are shown in Table VII. 



A fresh arsenite solution was made in a slightly different 

 manner from the former. To assist in dissolving the arsenious 

 oxide (4/95 grm.), 4 grm. of potassium hydroxide were added, 

 not enough to entirely form di-potassium hydrogen arseniate, 

 but more than enough to form potassium di-hydrogen arseniate. 

 At each titration 5 cra3 of a saturated solution of acid potassium 

 carbonate were added. 



* A crystal of potassium iodide was added, 

 f Girard., Ann. Chim. Series (6), xii, 275. 



