STARCHES. 221 



iodine they must, besides this, also contain soluble amylose. If the author 

 understands the above investigators correctly the starch granules con- 

 tain three constituents, namely; soluble amylose, which is colored blue 

 by iodine ( = starch granulose), insoluble amylose, which is not colored 

 by iodine ( = starch cellulose), and amylopectin. 



In the formation of paste the amount of amylose is not the essential, 

 but rather the quantity of amylopectin. The amylopectin is a slime- 

 like substance, insoluble in boiling water and dilute alkalies, only becom- 

 ing pasty therein, and not colored blue by iodine. Accordingly the 

 paste is a solution of amylose made thick by amylopectin. The amylo- 

 pectin, unlike the amylose, is only slowly transformed into sugar 

 with dextrin formation. Starch is insoluble in alcohol and ether. On 

 heating starch with water alone, or heating with glycerin to 190 C., 

 or on treating the starch grains with 6 parts dilute hydrochloric acid 

 of sp. gr. 1.06 at ordinary temperature for six to eight weeks, 1 it is con- 

 verted into soluble starch (AMYLODEXTRIN, AMIDULIN). Soluble starch 

 is also formed as an intermediate step in the conversion of starch into 

 sugar by dilute acids or diastatic enzymes. Soluble starch may be 

 precipitated from very dilute solutions by baryta-water. 2 



Starch granules swell up and form a pasty mass in caustic potash or 

 soda. This mass gives neither MOORE'S nor TROMMER'S test. Starch 

 paste does not ferment with yeast. The most characteristic test for starch 

 is the blue coloration produced by iodine in the presence of hydriodic 

 acid or alkali iodides. 3 This blue coloration disappears on the addition of 

 alcohol or alkalies, and also on warming, but reappears again on 

 cooling. 



On boiling with dilute acids starch is converted into dextrose. In 

 the conversion by means of diastatic enzymes we have, as a rule, besides 

 dextrin, maltose, and isomaltose, only very little dextrose. We are 

 considerably in the dark as to the kind and number of intermediate 

 products produced in this process (see Dextrins). 



Starch may be detected by means of the microscope and by the 

 iodine reaction. Starch is quantitatively estimated, according to SACHSSE'S 

 method, 4 by converting it into dextrose by hydrochloric acid and then 

 determining the dextrose by the ordinary methods. 



Inulin, (C 6 HioO 5 )x+H 2 O, occmys in the underground parts of many 

 Composite, especially in the roots of the Inula helenium, the tubers 



1 See Tollens' Handb., 191. In regard to other methods, see Wroblewsky, Ber. d. 

 deutsch. chem. Gesellsch., 30; Syniewski, ibid. 



2 In regard to the compounds of soluble starch and dextrins with barium hydroxide, 

 see Billow, Pfluger's Arch., 62. 



3 See Mylius, Ber. d. deutsch. chem. Gesellsch., 20, and Zeitsch. f . physiol. Chem., 11. 



4 Tollen's Handb., 2. Aufl.. 1, 187. 



