Oxidizers in the Hydrolysis of Starch and Dextrine, 383 



la. A few cubic centimeters of hydrogen dioxide were 

 added to l*25 cm3 of starch solution and diluted to 100 cm V One 

 drop of decinormal iodine brought out a fine blue color. Hence 

 hydrogen dioxide has no oxidizing effect on starch in neutral 

 solution. 



b. As already stated,* acid potassium carbonate by itself per- 

 mits a sharp reaction. In hot solution it has no noticeable 

 effect, since 4 cm3 of starch solution were boiled in 100 cm3 of 

 water with a few cubic centimeters of acid potassium carbo- 

 nate, and upon the addition of iodine to the cooled solution a 

 single drop gave a pale blue. 



g. A few cubic centimeters of both hydrogen dioxide and 

 acid potassium carbonate were added to a little starch solution 

 in about 100 cm3 of water. When the color began to come, an 

 abundance of red and purple resulted. Again, 3 cra3 of starch 

 solution were boiled in 100 cm3 of water in the presence of a few 

 cubic centimeters of hydrogen dioxide and acid potassium car- 

 bonate. Iodine added to the cooled solution produced an 

 abundance of red and purple. In both of these experiments 

 considerable iodine was taken up before the color came, but 

 this had no bearing upon the phenomenon, as hydrogen dioxide 

 and acid potassium carbonate together take up iodine, probably 

 forming iodate. The important feature of the experiment is 

 the production of a. compound coloring red with iodine when 

 the starch solution is treated with an oxidizing agent in the 

 presence of the acid potassium carbonate. 



II. The experiment was repeated with the substitution of 

 potassium permanganate for hydrogen dioxide. 



a. In neutral solution the starch was completely oxidized. 

 Into an Erlenmeyer flask 4 cm3 of the starch solution, l cm3 of 

 potassium permanganate and 120 cm3 of water were introduced, 

 brought to a boil and boiled for five minutes. Two drops of a 

 very dilute solution of sulphurous acid were then added and 

 the solution made acid in order to bleach the remainder of the 

 permanganate. The solution was cooled and made alkaline 

 with acid potassium carbonate. A drop of iodine produced 

 only a yellow color, and was shown to be free iodine by the 

 addition of fresh starch. 



b. The experiment was next made in alkaline solution and 

 resulted as in the previous experiment with hydrogen dioxide. 



In an Erlenmeyer flask, 4: sm3 .of starch solution, 10 cm3 of acid 

 potassium carbonate and l cm3 of potassium permanganate, 

 diluted to 125 cm3 , were boiled for five minutes. Three drops 

 of the dilute sulphurous acid were required to neutralize the 

 excess of permanganate in the acidified solution. The addi- 

 tion of iodine to the solution, cooled and made alkaline with 



* See Table I. 



