SOLUBLE STARCH, 105 



and dry the starch in the air. This gives a preparation that is readily soluble in hot 

 water, yielding a clear solution. A 2 per cent solution will remain clear or slightly opal- 

 escent for two days, after wliich it will become cloudy, but if no further change takes 

 place tliis will not interfere with its use for diastatic experiments. A concentrated (10 

 per cent) solution on cooling becomes salve-like. The solution will reduce only a minute 

 quantity of Fehling's solution, so that this need not enter into consideration in using the 

 starch for experimental purposes. Ten per cent hydrochloric acid will immediately turn 

 starch into soluble starch, differing in this respect from sulphuric acitl, for if the latter be 

 employed it will be necessary to use at least a 15 per cent solution and to conduct the 

 experiment at 40°. 



Brown and Morris (Jour. Chem. Soc. Trans., 18S9, lv, 449) subjected potato starch 

 to the action of 7.5 to 12 per cent hych-ochloric acid. With the former, the power of gela- 

 tinization was lost in 10 days; with the latter within 24 hours. This alteration is not 

 accompanied by the least change of structure of the starch-grain or in the behavior of the 

 starch-grain in polarized light. In hot water (60° to 70°) the grains form a perfectly 

 limpid solution, and from the solution there separates, on cooling, a substance in the form 

 of a white, flocculent, amori)hous precipitate which has all of the properties of soluble 

 starch prepared by the limited action of diastase or dilute acids on starch-paste at elevated 

 temperatures. Both in solution and in the solid state this soluble starch is colored intensely 

 blue in the presence of iodine. In solution it is without reducing power on copper solu- 

 tions, and it has a specific rotatory power (a)j 3.86= -|-216. Even after 20 days the 

 microscopic form of the granules is retained, notwithstanding the profound modification 

 in the starch. 



Lintner's method was modified by Lake (Jour. Soc. Chem. Industry, 1894, xiii, 264) 

 by centrifugalization of the starch-hydrochloric acid preparation. The starch is placed 

 in an equal volume of 5 to 10 per cent hydrochloric acid and centrifugalized, the action 

 of the centrifuge causing a very intimate penetration of the starch by the acid. The acid 

 is removed by washing with cold water and with dilute solutions of alkaUne carbonates, 

 after which the preparation is centrifugalized, and the starch collected and dried at a 

 temperature of 20° to 40°. Starch prepared in this way dissolves in hot water without 

 gelatinization. The process may also be carried out with nitric, sulphuric, phosphoric, 

 oxalic, lactic, acetic, and other liquid or volatile acids. 



Virneisel (Jour. Soc. Chem. Industry, 1899, xviii, 697) digested starch in a 1 to 2 

 per cent solution of mineral or organic acid, preferably sulphuric acid, at a temperature 

 of 50° to 55° for about 12 to 15 hours. Dextrin and sugar were not formed. 



Blumer (Jour. Soc. Chem. Industry, 1903, xxii, 310) slowly heated starch in a 1 per 

 cent solution of volatile acid for 5 to 6 hours at 115°, the acid afterwards being removed 

 by distillation. 



The foregoing processes were modified by Cross (Jour. Soc. Chem. Industry, 1903, 

 XXII, 1008) by heating the starch in a monocarboxylic acid with or without a dehydrat- 

 ing agent, such as alcohol or a concentrated solution of neutral salt. For instance, starch 

 dried at 100° is intimately mixed with one-third to one-half of its weight of glacial acetic 

 acid, heated in a steam-jacketed vessel for 1 to 2 hours, and the starch then freed from 

 acid and ckied. Formic or lactic acid may be employed, but preferabh^ in the presence 

 of a dehydrating agent to prevent gelatinization. 



Similar procedures were adopted by Wotherspoon (Jour. Soc. Chem. Industry, 

 1904, xxiii, 29). For instance, dried starch is treated with glacial acetic acid to the extent 

 of 10 to 50 per cent of its weight, and the preparation heated in a closed steam-jacketed 

 converter until the starch is soluble in hot water. If an aqueous acid be employed, an 

 inert dehydrating agent may be used, such as alcohol or brine, to prevent gelatinization. 

 The acid may be distilled off. 



