STARCH. 205 



When dried, starch, which has been treated with warm 

 water, forms a colorless, transparent, hard mass. 



Compounds. In the form of powder as well as of 

 jelly, starch combines with iodine, forming a body of 

 a deep blue color, which, when heated with water, 

 becomes colorless and on cooling turns blue again. 

 With bromine it turns orange-red. 



Starch combines with bases. Insoluble white amy- 

 lates of calcium and barium are produced by precipitat 

 ing baryta and lime-water with a hot solution of starch ; 

 lead amylate from a solution of starch with basic lead 

 acetate. 



Transformations. Heated to about 200, starch is 

 converted into dextrin. A solution of starch heated 

 with a solution of diastase, or boiled for some time 

 with water containing sulphuric acid, is changed first 

 into an isomeric modification, soluble starch, which is 

 soluble in hot and cold water and can be precipitated 

 from its solution by alcohol. Iodine colors the solution 

 blue, and baryta water gives a heavy precipitate. If 

 the action of the diastase or acids is continued further, 

 it is first converted into dextrin and then into grape- 

 sugar. Starch dissolves in very concentrated nitric 

 acid. If the solution is immediately mixed with water, 

 all the starch, employed at first, is precipitated as a 

 white, powdery body, xyloidine. This is a compound 



similar to gun-cotton C^/9\0. After being 



washed and dried, it takes fire even at 180, and burns 

 with violence. If to the solution in nitric acid are 

 added first sulphuric acid and then water, a similar 



body C 6 H 7 2 separates. By heating with 



nitric acid, starch yields the same products as grape- 

 sugar. 



Triacetyl-amylum, C 6 H 7 (O.C 2 IPO) 3 2 . Is formed 

 by heating starch with an excess of acetic anhydride 

 to 140. Amorphous mass, insoluble in water, alcohol, 

 18 



