Oxidizers in the Hydrolysis of Starch and Dextrins. 381 



starch, and the impurity coloring red with iodine is erythro- 

 dextrin, the second product of saliva digestion of pure starch. 



4th. The loss of iodine is due to the formation of erythro- 

 dextrin from this amidulin-like body, and erythrodextrin does 

 not use up iodine by any transformation to achroodextrins. 



Experiments showing the Loss of Iodine and its Correction. 



A few qualitative experiments on the sharpness of the reac- 

 tion between iodine and starch demonstrated no loss in getting 

 a reading under proper conditions, such as were used in the 

 titrations. 



Table J. 



Total 





Ordinary 







dilution. 



w/10 I sol. 



starch. 



Other reagents. 



Color. 



cm 3 . 



drops. 



cm 3 . 







75 



1 



2 



1-25 



a 







75 





blue 



75 



1 



<c 



KI, 1 crystal 

 (0*1-0-3 grm.) 



blue 



35 





a 



KI, few grams 



reds (fading) 



75 



7-10 



a 



Na 2 C0 3 , 1 grm. 



blue 



75 



5-6 



u 



K 2 C0 3 , 1 grm. 



blue 



75 



1 



a 



KHC0 3 , 1 grm. 



blue 



The iodine solution used was made up in the usual way, 

 12*685 grm. of iodine and 18 grm. of potassium iodide to the 

 liter. The arsenite solution in the following table contained 

 4*95 grm. of arsenious oxide to the liter and 70 cm3 of a satu- 

 rated solution of acid potassium carbonate. 



In 5 cm3 of iodine solution there are about 0*09 grm. of potas- 

 sium iodide, and about O06 grm. of potassium iodide are 

 formed from the free iodine in a titration, hence in an ordinary 

 titration of arsenite solution by iodine enough potassium iodide 

 (0*15 grm.) is present to bring a reading with one drop, in 

 accordance with the experiments above. The presence of too 

 much potassium iodide is, however, injurious to delicacy of 

 reading. The only alkalies which can be employed are the 

 acid carbonates. The influence of potassium iodide on the 

 starch reaction, as well as the influence of the alkalies, has 

 been ably shown by Lonnes.* 



Notwithstanding the fact that the following titrations were 

 made under favorable conditions, i. e., in the presence of acid 

 potassium carbonate and of a proper amount of potassium 

 iodide, Table II shows a considerable loss of iodine. The 

 action which brings about the loss, with a fixed amount of 

 starch, must be rapid, for it seems complete when 20 cm3 of 



* Zeitschr. anal. Chem., 1894, 409-436. 



