Crystallised Starch. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amsterdam, 

 Vol. XVIII, 1915, p. 305 309. - Verscheen onder den titel Gekristalliseerd zetmeel* 

 in Verslagen Kon. Akademie van Wetenschappen, Wis-en Natuurk. Afd., Amsterdam, 



Deel XXIV, 1915, biz. 240245. 



The fact that starch crystallises easily is not generally known. It is true 

 that Arthur Meyer supported the view that the starch grain is a 

 sphero-crystal 1 ), but convincing figures he does not give; his considerations are 

 hypothetical and not decisive as he did not make any microscopical examination 

 on soluble starch. Moreover, the highest temperature used by him was but 145 C. 

 and he continued the heating not long enough. 



Most species of starch, such as that of potato, wheat, barley, rye, rice, 

 maize, behave as follows. 



When a io/o solution, after previous boiling and gelatinising in distilled 

 water, is heated during fifteen minutes or half an hour at 150 to 160 C., the 

 grains dissolve to a perfectly clear, transparent liquid, in which, at slow cooling 

 a crystalline deposit sets off, consisting of very fine needles, which are either 

 isolated or united in groups of various shapes, not seldom resembling natural 

 starch, and which must undoubtedly be considered as crystallised starch on account 

 of their behaviour towards diastase and chemical reagents. 



The free needles, measuring but few microns or parts of microns, make the 

 impression of an amorphous sediment. The groups, formed by longer needles 

 have the shape of corn-sheaves or bundles of arrows (bolidesms) ; or of discs 

 (bolidiscs), reminding in size and form of the red blood-cells; or they are more 

 or less regular globules (spherites or sphere-crystals) from whose surface, however, 

 here and there project the crystal needles. 



Potato starch is very well apt to produce bolidesms and spherocrystals ; it 

 is sufficient to heat to 150 C., during a quarter of an hour, a 10% solution in 

 distilled water, previously boiled and gelatinised. After being kept 24 hours in a 

 cold room loose needles, bolidesms or sphere-crystals are precipitated, and their 

 crystalline nature is easily observable. What circumstances determine the union 

 of the needles to bundles is not yet well known, but certainly slowness of 

 crystallisation favours it, and the concentration has also some influence. Not 

 seldom the whole deposit consists of a magnificent mass of sphere-crystals (Fig. i). 

 The discs, to which I shall return presently, are formed from potato starch at 

 a somewhat lower temperature than the needles mentioned here. The two con- 



') Untersuchungen iiber Starkekorner, Jena 1895. Beitrage zur Kenntnis der Stiirke- 

 gallerten, Kolloidchemische Beihefte Bd. 5, pag. i, 1913. The observations and opinions 

 of Butschli, Untersuchungen iiber Strukturen, pag. 283, Leipzig 1898, are obscure. 



13' 



