Encyclopædia Britannica, Ninth Edition/Dextrin

DEXTRIN, or British gum, C 6 H 10 O 5 , is a substance produced from starch by the action of dilute acids, alkalies, and diastase or malt extract, and by roasting it at a temperature between 140 and 160 C. (284-320 Fahr.) till it is of a light brown colour, and smells like over-baked bread. Its name has reference to its powerful dextro-rotatory action on polarized light. The purest dextrin is prepared by boiling 25 parts of sulphuric acid with 125 of water, and adding by degrees a mixture of 100 parts of starch and 125 of cold water. The liquid is then lowered in temperature to 60 or 70 C. (H0-158 Fahr.), at which it is kept for some time ; it is next neutralized with chalk, filtsred, and evaporated. Dextrin is an uncrystallizable, insipid, odourless, yellowish-white, translucent substance, brit^e and friable when thoroughly dried. It dissolves in water and dilute alcohol ; by strong alcohol it is pre cipitated from its solutions as the hydrated compound, pe^io^s-HpO. Unlike starch it is not coloured blue by iodine. Diastase converts it eventually into maltose, C 12 H 22 U ; and by boiling with dilute acids and alkalies it is transformed into dextrose, or ordinary glucose, C 6 H 12 0,5. It does not ferment in contact with yeast, 1 and in the pure state has probably no reducing action on an alkaline copper solution. If heated with strong nitric acid it gives oxalic, and not mucic acid. Limpricht has shown that dextrin is present in the flesh-juice of the horse. Dextrin much resembles gum arabic, instead of which it is generally substituted for a great variety of purposes. It is employed for sizing paper, for stiffening cotton goods, and for thickening colours in calico printing, also in the making of lozenges, adhesive stamps and labels, and surgical bandages. In most technical operations the crude solution only is used.