96 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



conversion of raw starch into the so-called soluble starch, of which starch-paste and pseudo- 

 solulions and true solutions arc simple modifications, is one of hydrolysis or hydration 

 in the strictly chemical sense, but of adsorption, that is, an extramolecular union with 

 water that is of a physico-chemical character, such, for instance, as is observed in the 

 deposition of moisture on glass and in the taking up of water by hygroscopic substances, 

 in which there may be no true chemical union in the conventional meaning, but a mere 

 surface combination — certainly no hydrolysis or splitting-up of molecules. 



Starch-grains do not either gelatinize or pass into solution in their normal state, 

 because apparently of the existence of some form of protective covering which prevents 

 the water from reaching the starch-substance, but when the grains are crushed, or if the 

 coating is otherwise injured, they take up water rapidly and become gelatinous; but if 

 such grains are placed in water containing a sufficient quantity of some agent which liinders 

 or prevents the surface-combination with water, such as alcohol, acetone, alcohol and 

 ether, brine, etc., httle or absolutely no swelling or solution occurs. Analogous phenomena 

 have been observed with other so-called colloids, where it has been shown that swelling 

 may be augumented or inliibited by the presence of various substances. Starch in conmion 

 with organic colloidal substances is hygroscopic, and the so-called process of hydration 

 or hydrolysis to form soluble starch or "hydrate of starch" is explicable on the basis of 

 adsorption, that is, a physico-chemical affinity that is specific and selective, and supple- 

 mental to satisfied affinities according to the laws of stoichiometry. The water is conceived 

 to enter into a physico-chemical combination, the energy of this combination or adsorption 

 becoming more marked with an increase of temperature, and observed at its maximum when 

 starch is heated in the autoclave to form a solution so perfect as to be separable by methods 

 of filtration which prevent the passage of molecules in other than in true solution. 



Raw starch gradually heated in water slowly takes up water until at a certain level 

 of temperature adsorption occurs very actively, and the grains swell rapidly, the gelati- 

 nized capsules burst, and the whole disappears. Before any marked swelling occurs the 

 starch-grain loses its anisotropy, thus showing an intermolecular disorganization, but 

 this can not be regarded as a manifestation of hydrolysis or of the formation of a hydrate 

 in the chemical sense any more than in the case of particles of gelatin, which also when 

 dry are anisotropic or doubly refractive, but not after swelling. The combination is, of 

 course, actually chemical, because all of the so-called physico-chemical reactions are 

 technically chemical, but it is not chemical in the conventional sense any more than the 

 solution of sugar in water is chemical and thus a hydrate is formed. 



The striking analogies that have been shown in the behavior of starch, dextrin, gum, 

 cellulose, gelatin, glue, and proteins by the results of the investigations of Hofmeister 

 (Arcliiv f. exp. Path. u. Pharm., 1890, xxvii, 395; 1891, xxviii, 210), Pauli (Archiv f. 

 ges. Physiologic, 1897, lxvii, 219; 1898, lxxi, 1; Physical Chemistry in the Service of 

 Medicine, trans, by Fischer, 1907), Spiro (Beit. z. chem. Physiologic, 1904, v, 276), Ost- 

 wald (Arcliiv f. ges. Physiologic, 1905, cviii, 563), Fischer ((Edema, 1910), and others, 

 render it clear that the explanation of the phenomena of swelling, gelatinization, pseudo- 

 solution, and true solution, as determined by one of these substances, is in all essential 

 respects applicable to all. If, therefore, the phenomena in the case of gelatin are explicable 

 on a physico-chemical basis, the same will hold good for starch, and, therefore, the phenom- 

 ena attending the so-called hydration of starch are those of adsorption. Moreover, not 

 only are these parallelisms manifested in the behavior towards water and various aqueous 

 solutions and in the reversibility of the taking up of water, but also in changes brought 

 about in colloids by alterations in external conditions, every change leaving its effects 

 temporarily or permanently on the colloid. 



As regards the latter, reference may be made to the investigations of Syniewski (Ann. 

 d. Chem. u. Pharm., 1899, cccix, 282), who found that when a 5 per cent starch-paste 



