DEXTRIN GUM. 207 



up, and, for the purpose of removing other substances, 

 at first washed successively with ether, alcohol, a dilute 

 solution of sodium carbonate, with water containing 

 hydrochloric acid, and pure water, then dissolved by 

 boiling with water. The strained solution coagulates, 

 forming a jelly, which, on being dried, leaves the 

 starch behind as a colorless, gummy mass, that swells 

 up with water again to a jelly. Tasteless and inodor 

 ous. Becomes brown with iodine. 



17. Dextrin, C 6 H 10 5 , occurs in the vegetable king 

 dom, although not very widely distributed ; and is also 

 contained in muscular tissue. Is formed from starch 

 by heating to 180 ; heating with water to 150 ; by 

 boiling with dilute acids ; and by warming with water 

 and diastase to 65-70. Amorphous, gummy mass ; 

 attracts moisture from the air. Very easily soluble in 

 water, insoluble in absolute alcohol and ether. The aque 

 ous solution rotates the plane of polarization to the right, 

 and does not reduce an alkaline solution of copper. 

 By further action of dilute acids or diastase, it is con 

 verted into grape-sugar. It conducts itself towards 

 nitric acid the same as starch. 



Triacetyl-dextrin, Cq:i 7 (0 : C 2 H 3 0) 3 2 . Is obtained 

 by heating dextrin with acetic anhydride and is also 

 formed when, in the preparation of triacetyl-amylum, 

 the temperature rises to 160. Amorphous mass, in 

 soluble in water and alcohol ; soluble in acetic acid. 



18. Gum. (Arabin), C 6 H 10 5 , exudes spontaneously as 

 a concentrated solution from a great many trees, and 

 solidifies in large, transparent drops ; as, for instance, 

 gum Arabic and gum Senegal, of various species of 

 acacia, cherry and plum-tree gum. Colorless, transpa 

 rent, vitreous mass, with a conchoidal, shining fracture, 

 completely uncrystallizable ; without taste and odor. 

 Easily soluble in water, forming a thick, sticky, taste 

 less liquid (mucilage). 



Pure gum (gummic acid, arabin) combines with 

 bases. Gum Arabic consists essentially of the calcium 



