THE VOLATILE PAKT OF PLANTS. 



63 



dilute solution of caustic soda is used to dissolve the al- 

 buminoids, see p. 95. The starch and bran remaining, are 

 separated by diffusing both in water, when the bran rap- 

 idly settles, and the water being run off at the proper 

 time, deposits the pure starch, corn-starch of commerce, 

 also known as maizena. 



Starch is prepared by similar methods from rice, horse- 

 chestnuts, and various other plants. 



Arrow-root is starch obtained by grating and washing 

 the root-sprouts of Maranta Indica, and M. arundinacea, 

 plants native to the West Indies. 



EXP. 25. Reduce a clean potato to pulp by means of a tin grater. 

 Tie up the pulp in a piece of not too fine inuslin, and squeeze it repeat- 

 edly in a quart or more of water. The starch grains thus pass the 

 meshes of the cloth, while the cellulose is retained. Let the liquid stand 

 until the starch settles, pour off the water, and dry the residue. 



Starch, as usually seen, is a white powder which con- 

 sists of minute, rounded grains, and hence has a slightly 

 harsh feel. When observed under a powerful magnifier, 

 these grains often present characteristic forms and dimen- 

 sions. 



In potato-starch they are egg or kidney-shaped, and are 



distinctly marked with curved lines or ridges, which sur- 

 round a point or eye ; a, fig. 12. Wheat-starch consists of 

 grains shaped like a thick burning-glass, or spectacle-lens, 

 having a cavity in the centre, b. Oat-starch is made up 

 of compound grains, which are easily crushed into smaller 



