AMYLACEOUS AND SACCHARINE SUBSTANCES. 73 7 



CHAPTER II. 



SECTION I. 



AMYLACEOUS AND SACCHARINE SUBSTANCES. 

 STARCH. 



Syn. FECUL.A, AMYLIN ; C 12 H 10 O 10 ; in combination with 

 oxide of lead, C 12 H 9 O 9 + 2PbO, (Payen). Its composition, well 

 dried in vacuo at 212, is 



12 atoms of carbon. . . . 917.22. . 44.91 

 10 atoms of hydrogen. . . 125.00.. 6.11 

 10 atoms of oxygen. . . . 1000.00. . 48.98 



204.22.. 100.00 



Starch is separated from a variety of vegetable substances 

 containing it, from the grains of the different cereals, many roots 

 such as the potato, the stems of many monocotyledonous plants 

 particularly the palms, and from several lichens. It is con- 

 tained in the cavities of the vegetable cells, in the form of small 

 white and brilliant grains, which are not crystalline, but have a 

 rounded outline without any determinate form. It is so far an 

 organised substance, that each grain has a species of envelope, 

 which resists the action of cold water, while the inner portion 

 is observed by the microscope to be composed of concentric 

 layers of unequal thickness, as if the layers produced during 

 the day exceeded in thickness those formed during the night. 

 (Fritzsche). The grains of the starch of different plants differ 

 in size, those of the potato being about -jrfor, of wheat -s-U, of 

 millet, TTT^irath of an inch in diameter, according to observations 

 of Raspail. But it is also known that the starch grains of the 

 same plant differ in size at different stages of its development. 



The purest starch is obtained from potatoes, which are 

 reduced to a pulp and washed on a sieve. The grains of starch 

 are separated and passed through; they may be washedrepeatedly 

 with cold water. Potatoes yield 15 to 17 per cent, of starch ; 

 wheaten flour consists essentially of starch and another vege- 

 table principle gluten. When made into dough with a little 

 cold water, inclosed in a linen bag ?> and gently pressed by the 

 hand in water, so long as a milky juice exudes, these two subs- 



2 c c 



