POWDERED DRUGS AND FOODS. 787 



MoNTSERRAT arrowroot closely resembles the Bermuda starch, 

 but the grains are a little larger and more of them show the 

 cleft. St. V^incent arrowroot is slightly darker in color and 

 is in the form of masses or granules, which are sometimes 20 

 mm. in diameter. The starch grains resemble those of the Ber- 

 muda arrowroot, but the grains having clefts are more numerous. 

 The arrowroot starches all show a distinct cross with the 

 micropolariscope and a marked play of colors when a selenite 

 plate is used. These starches usually contain about 15 per cent, 

 of water, the remainder being composed of the starch grains. 



228. POTATO STARCH occurs as a more or less finely 

 granular powder, and appears to have less tendency to form 

 coherent masses than arrowroot starch. The grains (Figs. 95; 

 96; 316, A) are somewhat shell-shaped, having distinct lamellae 

 and a circular point of origin of growth, which is at the smaller 

 end of the grain. They vary in size from 50 to 100 fx,, there being 

 a large number of smaller, somewhat ellipsoidal or spherical 

 grains, and a few 2- or 3-compound grains. Under the micro- 

 polariscope the grains show a distinct cross (Fig. 95), and a 

 striking play of colors when a selenite plate is used. On heating 

 the starch to a temperature of 65 C. or treating it with very 

 dilute alkali or acid solutions, the grains swell to four times their 

 original size and finally burst, passing through the successive 

 changes in structure illustrated in Fig. 96. 



229. CORN STARCH. This occurs as a fine, somewhat 

 cream-colored, mobile powder, which is practically free from 

 cohering particles. The starch grains (Fig. 316, D) are more 

 or less polygonal or somewhat rounded, usually wdth a distinct 

 circular, or 2- to 5-rayed cleft in the cenfer, and vary from 10 

 to 35 fjL in diameter. When examined by means of the micro- 

 polariscope the grains show^ a distinct cross, but the display of 

 colors when the selenite plate is used is less pronounced than in 

 potato starch. This starch frequently contains traces of alkalies, 

 which may be detected by adding 0.5 Gm. of the starch to 2 c.c. 

 of an aqueous solution of fuchsin, when the latter is decolorized. 

 Corn starch is official (p. 642). It should also be stated that the 

 different kinds of corn produce starches that are somewhat 

 different in character (p. 229). 



