THE VOLATILE PART OF PLANTS. 55 



wheat plants, and there in very small quantity. Accord- 

 ing to Meissl, the soy bean contains 10 per cent of dex- 

 trin. 



Dextrin is easily prepared artificially by the trans- 

 formation of starch, or, rather, of amidulin derived from 

 starch, and its interest to us is chiefly due to this fact. 

 When starch is exposed some hours to the heat of an 

 oven, or for 30 minutes to the temperature of 415° P., 

 the grains swell, burst open, and are gradually converted 

 into a light-brown substance, which dissolves readily in 

 water, forming a clear, gummy solution. This is dex- 

 trin, and thus prepared it is largely used in the arts, 

 especially in calico-printing, as a cheap substitute for 

 gum arable. In the baking of bread it is formed from 

 the starch of the flour, and often constitutes ten per cent 

 of the loaf. The glazing on the crust of bread, or upon 

 biscuits that have been steamed, is chiefly due to a coat- 

 ing of dextrin. Dextrin is thus an important ingredient 

 of those kinds of food which are prepared from the 

 starchy grains by cooking. 



Commercial dextrin appears either in translucent 

 brown masses or as a yellowish-white powder. On ad- 

 dition of cold water, the dextrin readily dissolves, leaving 

 behind a portion of unaltered starch. When the solu- 

 tion is mixed with strong alcohol, the dextrin separates 

 in white flocks. With iodine, solution of commercial 

 dextrin gives a fine purplish-red color. 



There are doubtless several distinct dextrins scarcely dis- 

 tinguishable except by the different degrees to which they 

 affect polarized light or by various chemical deportment 

 (reducing effect on alkaline copper solutions). They are 

 characterized as erythroijextrins, which give with iodine 

 a red color, and achroodextrins, which give no color with 

 iodine. Investigators do not agree as to the precise num- 

 ber of dextrins that result from the transformation of 

 starch. 



