GELATINIZATION, REFRACTIVE INDEXES, AND REACTIONS IN POLARIZED LIGHT. 175 



Table 20. 



Kind of starch. 



Swelling 

 begins. 



Gelatinization 

 begins. 



Rye 



Corn 



Horse chestnut {/Esculus hippo- 



caxtanum) 



Barley 



Chestnut (Castanca i-cscn) 



Potato 



Rice 



Arum maculatum 



Arrowroot (Marania arund.).. . 



Tapioca (Jatropha uHlis.) 



Arum esculentum 



Sago (Sagus rumphii) 



Buckwheat 



Acorn 



Wheat 



45.00 

 60.0 



62.5 



37.5 



62.6 



46.25 



63.75 



50.0 



66.25 



45.6' 



55.0 

 57.5 

 50.0 



50.0 

 55.0 



56.25 



57.5 



58.75 



58.75 



58.75 



58.75 



66.25 



62.5 



63.75 



66.25 



68.75 



77.6 



65.0 



Gelatinization 

 complete. 



forming ultimately a paste or a pseudo-solution of varying degrees of viscosity, according 

 to the |)ercentagc and kind of starch and various attendant conditions. Lippmann (Jour, 

 f. imxkt. C'hcniie, 1861, lxxxiii, 51) studied the temperatures at which swelling and at 

 which gelatinization begin, and at which gelatinization is complete. Tlie starch and 

 water were put in a beaker 

 in a water-bath and slowly 

 heated, and the preparation 

 was subjected to microscop- 

 ical examination at proper in- 

 tervals. His results are given 

 in table 20. 



Lintner (Tollen's Handb. 

 d. Kohlenh., ii, 207) records 

 that potato starch suddenly 

 goes into a paste at about 62° to 

 64°, while cereal starches un- 

 dergo the same change at 75° 

 to 80°. (See table 23, page 178.) 



According to Dafert 

 (Meyer, Die Starkekorner, he. 

 cit. p. 134) rice starch gelatin- 

 izes at 73°. Whymper (»Seventh Int. Cong. Appl. Chem., London, 1909; Jour. Soc. 

 Chem. Ind., 1909, xxviii, 800) recorded the temperatures of gelatinization of Ijarley, 

 corn, rye, potato, rice, wheat, and tapioca starches by subjecting them to a gradually 

 rising temperature and examining them microscopically. The values differed in most 

 cases from those of pre\'ious observers, and also varied mth the state of maturity of 

 the grains. The larger granules of any given starch were found to almost im^ariably 

 succumb more cjuickly than the smaller granules to both wet and dry heat, and to 

 diastase and mineral acids. 



Gelatinization may be bi'ought about by various chemicals, such as potassium hy- 

 droxide, chloral hydi'ate, chromic acid, etc. (see page 172). 



55.0 

 62.5 



68.75 



62.5 



62.5 



62.5 



61.25 



62.5 



70.0 



68.75 



68.75 



70.0 



71.25 



87.5 



07.5 



REFRACTIVE INDEXES OK STARCHES. 



The refractive indexes of starches from tliiferent sources were determined by Ott 

 (Osterr. bot. Zeitschr., 1899, xxxix, 313). The figures recorded are given in table 21. 



Table 21. 



REACTIONS IN POLARIZED LIGHT. 



The behavior of starch-grains toward polarized light seems to have been discovered by 

 Biot (Compt. rend., 1844, xviii, 795). Since then many observers have noted the differ- 

 ences in the form and distinctness of the interference figure or "cross"; and also differences 

 in the degree with which light is transmitted by grains of the same and of different starches, 



