17G DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



aiul ill the c'olm-s with a sclenite plate. The point of intersection of the two parts of the 

 cross usually corresponds to the position of the hilum, or in compound grains to each of 

 the many liila. In grains having a centric hilum, the form of the cross corresponds with 

 that of the Greek cross or cross of St. George, but in grains with eccentric hila, the figure 

 corresponds with that of the Latin cross, the cross-arm being in any position between a 

 short distance from the center and the almost extreme end of the part corresponding to the 

 upright, and in such grains the arms become curved, sometimes so much so as to resemble 

 the hanging branches of the weeping-willow tree, losing the appearance of a cross. Many 

 illustrations will be seen in the accompanying plates. Muter {loc. cit.) found that the follow- 

 ing starches give a well-marked cross: Potato, canna, maranta. Natal arrowroot, turmeric, 

 mother-cloves, sago, tapioca, and cinnamon. The following do not give a well-marked cross : 

 Wheat, barley, rye, acorn, and cacao. The following give a faint cross : Ginger, banana, 

 nutmeg, sorghum, oat, and corn. The following give an indistinct cross: Pea, bean, and 

 lentil. Rice gives a cross that is distinct and well-marked, and pepper shows a cross by 

 high magnification. 



The polariscopical properties are destroyed by all agents which cause a swelling of 

 the grains, but they are not affected after prolonged subjection of grains to dilute acid, 

 which renders the grains soluble without destroying their skeletal structure. 



The employment of polarized light for the microscopic detection of the presence of 

 foreign starches has been proposed by Gastine (Compt. rend., 1907, cxliv, 35; Jour. Soc. 

 Chem. Ind., 1907, xxvi, 108). A small quantity of the starch is suspended in a drop of 

 water, placed on a microscopic slide, and dried by exposure at room temperature and 

 finally by heating for a few moments at 120° to 130°. The preparation is then mounted 

 in Canada balsam and examined in ordinary polarized light, and also with the addition 

 in the polariscope of a selenite plate. With ordinary polarized light, the grains of rice 

 starch mth a magnification of 300 appear brilliantly illuminated in the dark field and 

 present a granitic structure. In the cliromatic polarized light obtained by means of selen- 

 ite, the blue and orange tints present a characteristic network of lines. Corn starch gives 

 a similar network, but its meshes are much larger than those obtained with rice starch; 

 corn starch also polarizes brilliantly. Millet, buckwheat, and rye starches, and many 

 others, show appearances similai" to those of rice and corn starches. The characteristic 

 form of the grains of bean and pea starch and their very brilUant polarization render 

 their determination easy. In the case of wheat starch, the groups formed of these grains 

 are of very varied size and irregularly placed, giving a very characteristic appearance 

 under the microscope ; seen in chromatic polarized light they do not present a symmetric 

 network of Unes. 



CHARACTERS OF STARCH-PASTE AND PSEUDO-SOLUTIONS FORMED BY STARCHES FROM 



DIFFERENT SOURCES. 



The characters of the starch-paste and also of the pseudo-solution vary with different 

 kinds of starches. This has been recognized in technical trades for many years, and on 

 this account preference is given to certain starches in the stiffening, sizing, and finishing 

 of fabrics. Potato starch yields a preparation by boiling that is poorly adapted to these 

 purposes, whereas wheat and corn starch yield an excellent product; but where a starch 

 is normally not of high value in this respect it may be rendered so by various means, as, 

 for instance, by the process suggested by Bellmas (Osterr. Chem. Zeitung., 1902, 366), wliich 

 is to digest potato starch at 55° in a 2 per cent hydrochloric acid, then forining a limpid 

 preparation by boiling. Various of the methods employed for making "soluble starch" 

 and liquefying starch-paste may be used (see page 101). In the experiments of Saare and 

 Martens (Zeit. Spiritusind., 1903, xxvi, 436) it was found that the length of time the starch 

 was heated at the boiling-point had a considerable influence upon the stiffening power of 



