110 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



solved in a small quantity of water, poured into a large quantity of alcohol under constant 

 stii-ring, the precipitate washed in absolute alcohol and ether, and finally dried in vacuo. 

 This method jdelds a snow-white preparation which contains little ash. It gives an intense 

 blue reaction with iodine; it does not reduce Fehling's solution; and it is soluble in water to 

 the extent of about 4 per cent. By the prolonged boiling of a dilute solution a small amount 

 of reducing substance is formed. If a strong solution of alkali is used, as by Biilow (Archiv 

 f. d. ges. Physiologie, 1895, lxii, 131), decomposition continues beyond the starch stage. 



Wr6blewski (Chem. Zeit., 1898, xxii, 375) reported a process for preparing a soluble 

 starch by means of caustic potash that can be filtered tlirough porcelain. On a small 

 scale, the soluble starch can be prepared by rubbing 20 grams of starch in a mortar wth 

 100 c.c. of cold water, pouring tliis into a 2-liter flask, adding about 1 liter of 0.5 per cent 

 potassium hydrate, and boiling under an inverted condenser for VA to 2 hours until it becomes 

 limpid and of a pale-yellow color. The preparation is neutralized with acetic acid, pre- 

 cipitated with an equal volume of alcohol, filtered, and filtrate washed successively with 

 50 per cent, 95 per cent, and absolute alcohol, and finally with ether, and then dried in 

 vacuo. The snow-white powder thus obtained is soluble to the extent of about 3 per cent 

 in water: and it contains about 0.4 to 0.6 per cent of ash. The less the ash the stronger 

 the alcohol necessary to cause precipitation. 



The caustic-alkaU processes for producing soluble starch were modified by Kautorwicz 

 (Jour. Soc. Chem. Industry, 1904, xxiii, 1038; 1905, xxiv, 144) by the introduction of alco- 

 hol, acetone, mixtures of alcohol and ether, etc., into the process to prevent the gelatinization 

 of the starch while it is being rendered soluble by the action of the alkali. The starch is 

 mixed with 50 to 90 per cent alcohol, and to this is added two-fifths the weight of the starch 

 of a solution of caustic soda at 30° Baume. The mass thickens, and is set aside for an hour, 

 then neutralized with acetic acid, and the resulting precipitate filtered off and diied. One 

 part of the dried product with 10 parts of water yields a viscous, hquid-Uke paste. 



Both oxidizing agents and caustic alkalis have, as shown, been found valuable in ren- 

 dering starch into a soluble form. Syniewski (Ber. d. d. chem. Gesellsch., 1897, xxx, 2415; 

 1898, XXXI, 1791) combined both by using sodium peroxide. 60 grams of sodium peroxide 

 were dissolved in 500 grams of water and rubbed up with 50 grams of starch in 500 gi-ams 

 of water, and set aside for an hour, after which the preparation was precipitated v/ith 

 95 per cent alcohol, the precipitate dissolved in water, neutralized with acetic acid, and 

 again precipitated with alcohol. By repeated solution and precipitation a snow-white 

 powder was obtained which is A-ery soluble in hot water, and soluble to the extent of 12.5 

 per cent in water at ordinary temperature. It is colored blue with iodine, does not reduce 

 Fehling's solution, and has a rotatory power at 20° of -|- 182.66° for a 2.5 per cent solution 

 and +189.5° for a solution of 12.5 per cent. In his second ai-ticle he gives the rotatory 

 power of a 10 per cent solution as (a)Di20 = +195.3°. Solutions containing more than 12.5 

 per cent could not be read in the polarimeter because of the deposition of a white precipi- 

 tate, which precipitate, by analysis, he found to be formed from the soluble starch, pre- 

 sumably by dehydration, and therefore a reversion product. This substance was also 

 formed in solutions which gelatinized upon cooling, thus giving rise to a gelatinous mass 

 identical with ordinary starch-paste. He describes the reactions with baryta-water, 

 acetylchloride, and benzolchloride, and also the invertive action of water under pressure, 

 and of alcohol, and diastase. 



A form of starch which possesses all of the properties of starch gelatinized at high tem- 

 peratures may be prepared by treatment with ammonium thiocyanate, according to the 

 process of the Arabel Manufacturing Co. (Jour. Soc. Chem. Ind., 1909, xxviii, 213). 100 

 parts of dry starch are mixed with 80 parts of a 50 per cent aqueous solution of this salt, 

 to which 40 parts of alcohol are added. The product swells in cold water to form a paste. 

 The thiocyanate can be removed by washing with alcohol, acetone, etc. 



