92 STARCH. 



granulose. The mass thus obtained cannot be regarded as a true 

 solution of starch, and it filters with extraordinary difficulty, 

 leaving a gelatinous residue on the filter, however dilute the 

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

 jected 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 HioO 5 but n (C 6 Hio0 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 -f H 2 0] (mol. = 990) + 5H 2 = 6C 6 H 12 O 6 (mol. = 1080). 



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

 been shown, by an application of Raoult's method, that the molecule 

 of soluble starch must probably be represented by the formula 5 (C 12 

 H 20 0io)2o- 2 Formulae based on analyses of the supposed compound of 

 starch with iodine are probably valueless, since there is but little rea- 

 son to suppose that any such definite compound exists. 



2. Soluble Starch (Amylodextrin) (C 6 H 10 5 ) n . 



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 contains 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 =:-f- 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, Anna/, d. Chem. Bd. CLX. (1871),'S. 40. 



