108 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



did not form uii osazone, and tliorefore it was not regarded as being saccharine. The 

 reducing substance differed essentially from tlextrin because of its being precipitated 

 from concentratetl solution by copper sulphate, and therefore more like a gum. 



Thompson (Jour. Soc. Chem. Industry, 1904, xxiii, 29) treated starch in a neutral, 

 alkaline or acid medium, preferably at high temperature, with more permanganate than 

 necessary to oxidize all of the extractive impurities, the treatment being continued until 

 all the starch was converted into a soluble form. 



Wolff and Roux (Compt. rend., 1905, cxli, 1046) modified the permanganate process; 

 they also used bichromate and chlorine instead of permanganate, and they extended our 

 knowledge of the properties of soluble starch. Starch was mixed with twice its weight of 

 a 1 per cent solution of potassium permanganate containing 10 to 15 per cent of sulphuric 

 acid, or 6 to 7 per cent of hydrochloric acid. The liquid becomes decolorized in about 

 2 hours, when the starch is filtered off, washed, and dried at 30°. A 5 per cent paste made 

 with distilled water is little less viscid than ordinary paste, and generally behaves like 

 ordinary starch-paste, but if treated at 70° in the presence of traces of basic substances 

 such as ammonia, or hydroxides, or carbonates of alkalies or alkaline earths, etc., there 

 occurs immediate liquefaction. This liquefying action takes place very slowlj^ at ordinary 

 temperatures, it is at its maximum at 70° to 75°, and it is somewhat different from the 

 liquefying action of malt because of its persisting above a temperatiu'e of 80°. The hot 

 solutions of this liquefied starch gelatinize as the temperatm-e falls, and become a jelly 

 at ordinary temperatures, and again pass into a limpid solution upon heating. 



Unless the action of the permanganate is checked the starch is gradually broken 

 down. Leitner (Zeitsch. f. angew. Chemie, 1890, 546) followed the progress of the actions 

 by testing the preparation from tune to time with iocUne in the manner pursued when 

 diastase is used. He recorded that the color reaction, which at first is blue, changes to 

 violet, red-violet, red, and reddish-brown, which becomes weakened, until finally there is 

 an absence of color response. The products, he states, are different from ordinary dextrins, 

 as is shown by their forming precipitates with basic lead acetate and barium hydroxide, 

 and by their acid reaction. They have a slight reducing power, and upon boiling expel 

 carbon dioxide from carbonates. 



Glycerol breaks down starch into soluble starch and, if the action is continued or is 

 carried on at a higher temperature, dextrins and related bodies are formed. Zulkowsky 

 (Ber. d. d. chem. Gesellsch., 1891, xxiii, 3295) found that starch heated in glycerine is 

 first changed to soluble starch, and that as the temperature rises erythrodextrin and 

 then acliroodextrin are formed, together with a series of bodies wliich are increasingly 

 soluble in alcohol and which could be separated by means of the differences in solubility. 

 Difficulty was met with in removing the last traces of glycerine, owing probably to 

 the formation of glycerides. This research was supplemented by another bj^ the same 

 author in conjunction with Franz (Chem. Centralbl., 1894, ii, 918; 1895, iii, 557), who 

 studied somewhat in detail the varying products formed at different temperatures. At 

 190° soluble starch is produced which gives a deep-blue reaction with iodine and has a 

 specific rotation of-|-188.3°. This starch is precipitated by alcohol, lime-water, or baryta- 

 water. The alcohol precipitate, after drying and upon keeping, is gradually converted 

 into the insoluble form. When kept in strong solution it gradually gelatinizes and becomes 

 insoluble. At 200° erytlu-odextrin is formed, and at 210° achroodextrin. Wlien the prepa- 

 ration is subjected to prolonged heating related carbohydrates are produced, one resembling 

 gum arable. Pregl (Monatsch. f. Chem., 1901, xxii, 1049) used 10 times the volume of 

 glycerine and purified the product by filtering the solution into 60 per cent alcohol, 

 collecting and drying the precipitate. The specific rotatory power of the aqueous 

 solution was found to be (a)D = +191.26°. From this preparation he made and studied 

 acetyl derivatives. 



