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, C 6 H 7 (O.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 



