Dextrine

Dextrine (syn. 'British gum,' 'torrefied starch'). When starch is carefully heated to 392° (200° C.), or until vapours arise from it, it becomes soluble in cold and hot water, and loses its gelatinous character; it also has the property, when viewed by polarised light, of turning the plane of polarisation to the right; hence its name. It is often used as a substitute for gum-arabic in the processes of calico-printing, and for stiffening different goods; it is also applied to the back of postage-stamps. Its value as a substitute for gum consists in its being more flexible and less brittle when dry than that substance. Starch may be converted into dextrine by the long-continued action of dilute acids at a high temperature; also by the action of Diastase (q.v.). Dextrine and starch are isomeric, both being composed of C₆H₁₀O₅; but dextrine may be distinguished from the latter body by its not being rendered blue by iodine, which gives with it a dingy purple tint.