746 AMYLACEOUS AND SACCHARINE SUBSTANCES. 



parated however from starch and pure, gluten is scarcely 

 digestible. 



It is to the presence of gluten that wheat flour owes 

 its property of forming a tenacious paste with water, and also 

 a light spongy bread. In baking leavened or loaf bread, the 

 dough is mixed with a quantity of yeast, or in its absence with 

 a portion of sour dough called leaven, and set aside in a warm 

 place, which occasions the saccharine matter of the flour to 

 undergo the vinous fermentation. The carbonic acid gas then 

 evolved expands the gluten into vesicles and causes the rising 

 the dough, which then forms a light loaf when heated in the oven. 



Gluten is not a pure principle ; when digested in hot 

 alcohol till every thing soluble is taken up, it leaves a bulky 

 substance of a greyish colour which has been called vegetable 

 albumen. The latter is soluble in water, but when the solution 

 is heated the albumen coagulates and becomes insoluble ; it is 

 also coagulated by the stronger acids. The true gluten, obtained 

 by evaporating the alcoholic solution, retains its adhesive pro- 

 perty and is soluble both in acids and alkalies. It is not 

 precipitated from a solution in acetic acid by the acetate of 

 lead or persulphate of iron, but abundantly by the chloride of 

 mercury and infusion of gallnuts. 



Inulin. This variety of starch was discovered by V. Rose in 

 the root of the Inula Helenium, to which it owes its name. It 

 is also found in various other roots, and in some lichens. It is 

 conveniently obtained from the roots of the dahlia. The latter 

 are rasped, washed with cold water and expressed, then boiled 

 with water, and the hot solution filtered through linen. This 

 solution may be clarified by white of egg, if muddy, evaporated 

 till a pellicle forms on its surface, and then allowed to cool ; the 

 inulin is deposited in a pulverulent form. It is collected on a 

 filter and washed well with cold water. Inulin is a very fine 

 white tasteless powder, of density 1.336, very soluble in boiling 

 water, but not gelatinizing, and requiring 50 parts of cold water 

 to dissolve it. Iodine makes it yellow, and insoluble in cold 

 water. It is insoluble in cold alcohol, soluble in acids, which 

 change it with the aid of ebullition into sugar, and more readily 

 than ordinary starch. It is converted by nitric acid into malic 

 and oxalic acids, without a trace of mucic acid. It was found 



