92 STARCH. 



finally burst, yielding a uniform viscous mass of starch-paste of which 

 the chief component is the granulose. The mass thus obtained cannot 

 be regarded as a true solution of starch, and it filters with extra- 

 ordinary difficulty, leaving a gelatinous residue on the filter, however 

 dilute the starch-paste may be which is used for the filtration. When 

 subjected to hydrolytic agencies such as superheated water, dilute 

 acids and enzymes the starch passes rapidly into true solution, 

 yielding at the same time a series of successive products to be 

 described below. 



Many attempts have been made to assign a definite formula to this 

 substance. The outcome of these is that the molecule of starch is 

 certainly not C 6 H 10 O 5 but n (C 6 H 10 O 5 ), where n is not less than 5 or 6 

 and is probably much larger. 



When starch is converted into dextrose by treatment with dilute boiling 

 sulphuric acid, it is found that 99 parts of starch yield 108 of dextrose 1 . Thus 



[(C 6 H 10 5 ) 6 + H 2 0] (mol. = 990) + 5H 2 = 6C 6 H 12 6 (mol. = 1080). 



Most recently, and in continuation of previous researches, it has been shown, 

 by an application of Eaoult's method, that the molecule of soluble starch must 

 probably be represented by the formula 5 (C 12 H 20 10 ) 20 2 . Formulae based on 

 analyses of the supposed compound of starch with iodine are probably valueless 

 since there is but little reason to suppose that any such definite compound exists. 



2. Soluble starch (Amylodextrin) (C 6 H 10 O B ) B . 



When starch-paste, heated to 40 C. on a water-bath, is digested 

 with a small amount of saliva and the whole stirred so as to effect a 

 thorough mixture of the two, the paste rapidly loses its opalescent 

 appearance, becoming limpid and clear like water : the moment this 

 change has taken place the digesting mixture should be boiled to cut 

 short the further action of the ptyalin. The fluid thus obtained con- 

 tains the first product of the hydrolysis of starch to which the name of 

 ' soluble starch ' has been given. Its solution filters readily, and the 

 filtrate yields with iodine the pure blue characteristic of the original 

 unaltered starch. On the addition of an excess of alcohol the soluble- 

 starch is precipitated, the precipitate after drying, being but little 

 soluble in cold water although it readily dissolves in water at 60 

 70 C. It also yields a characteristic precipitate with tannic acid, 

 and differs in this respect from the dextrins 3 . It is dextrorotatory 



(a) D = + 194-8" [(^ = 216"], 

 and does not reduce Fehling's fluid. The same substance may be 



1 Sachsse, Sitzb. d. Natforsch. Gesell. Leipzig, 1877. Chem. Centralb. 1877, 

 No. 46. 



2 Brown and Morris, JL Chem. Soc. Vol. LV. July, 1889, p. 462. 



3 Griessmayer, Annal d. Chem. Bd. CLX. (1871), S. 40. 



