SOLUBLE STARCH. 109 



Iodine was employed by Rodenwald and Kattein (Sitzungsber. d. Berliner Akad., 1899, 

 xxxiii-xxxiv, 62S), who heated starch in Lugol's solution in the autoclave for 15 min- 

 utes at 130°. A greenish-brown liquid is formed, which as stated consists essentially of 

 iodide of starch and some sugar. The starch iodide, they found, can be obtained pure by 

 dialysis and filtration. The quantity of iodine in combination was ascertained to be con- 

 stant at 14.3 to 14.8 per cent. The starch iodide is decomposed by heating, and as the 

 iodine is freed it is removed by a current of steam, leaving a clear solution. On cooling, 

 granules separate which give a blue reaction with iodine, and when dried the granules 

 are insoluble in cold water, but form a paste on boiling, and swell in potassium hydrate. 

 Some of the grains measured 0.02 mm. in diameter. 



Formaldehyde has a marked decomposing action on starch. Syniewski (Ann. d. Chem. 

 u. Pharm. 1902, cccxxiv, 201; Jahr. ii. d. Fort. d. Tierchemie, 1902, xxxii, 100) put potato 

 starch in 5 times its weight of 40 per cent formaldehyde, and at the end of two months 

 the starch was found to be completely dissolved. The solution was opalescent, but showed 

 no iodine reaction. Upon evaporation he obtained a homogeneous mass consisting of 

 trioxymethylen and a crystalline condensation product. The addition of water caused a 

 gradual disintegration of the latter, as was indicated by changes through a scale of colors 

 from brown to red and ^•iolet and blue, owing to the separation of the formaldehyde. 

 This cleavage could be accelerated by the presence of acid. The product present which 

 gi\'es the blue reaction with iodine he regards as amylodextrin or a body closely related 

 to it. He notes that amylodextrin otherwise prepared is dissolved at once in formalde- 

 hyde, with a transition of colors the reverse of that which is observed when the formalde- 

 hyde combination is broken up; and the reverse play of colors is also found to occur 

 when the solution is diluted. The amjdodextrin thus prepared undergoes crystallization 

 upon evaporation of the solution. Under the microscope, stars composed of needles were 

 first seen, and these were surrounded by a substance arranged in radial concentric layers. 

 These bodies were deceptively like starch-grains, and under the polariscope the similarity 

 was further shown by the double refraction and the interference figure. This amylodextrin 

 was found to form a definite dark-blue iodine compound. 



Reichard (Zeit. ges. Brauw., 1908, xxxi, 161) confirmed Syniewski's views regarding 

 the formation of a formaldehyde-amylodextrin compound by the action of 40 per cent 

 formaldehyde at ordinary temperature. He showed that at higher temperatures the process 

 goes on very rapidly, anil that the temperature of gelatinization is reduced with an increase 

 in the concentration of the formaldehyde. At 15° to 16° a 38 per cent solution of formalde- 

 hyde gelatinizes the starch completely in two daj'S. At 25° 1 gram of starch in 10 c.c. 

 of the same solution of formaldehyde was completely gelatinized in 7 to 8 hours. The 

 action is less rapid if the formaldehyde is neutralized. 



Potassium hydrate was used by B6champ (Compt. rend., 1854, xxxix, 653) to dissolve 

 starch, and it has since been used by a large number of investigators and is one of the 

 most valued agents when pure soluble starch is desired, because it, unlike dilute acids, 

 diastase, glycerol, permanganate, and most other agents, does not give rise to dextrin or 

 to any reducing substance ; in other words, with a weak solution of alkali the decomposition 

 of starch ceases at the stage of liquefaction. Tollens (Nachricht d. k. Gesellsch. d. Wis- 

 sensch, etc., Gottingen, 1873, 762) also used potassium as well as sodium hydroxide to 

 prepare soluble starch. 



Wr6blewski (Ber. d. d. chem. Gesellsch., 1897, xxx, 218) prepared soluble starch in 

 the following way: 100 grams of rice starch are rubbed with a small quantity of a 1 per 

 cent solution of potassium hydrate, and set aside for 2 to 4 hours, then more of the solution 

 is added until the whole has attained a volume of 600 to 800 c.c. This jelly-mass is heated 

 on a water-bath, stirred until fluid, and then boiled for 20 to 30 minutes, filtered, acetic 

 acid added to slight acidity, precipitated with alcohol, dissolved and precipitated, redis- 



