738 AMYLACEOUS AND SACCHARINE SUBSTANCES. 



tances are in a great measure separated, the gluten remaining in 

 the bag, and the grains of starch being diffused through the water, 

 from which they afterwards subside. On the large scale, wheaten 

 meal coarsely ground is mixed with cold water in large vats, in 

 which, with a certain addition of sour water from a former 

 process, the liquid ferments for seven or eight days, and the 

 starch subsides. The acetic acid formed in the fermentation 

 dissolves the greater part of the gluten of the flour, and the 

 bran is separated from the starch by a fine sieve. The starch 

 is afterwards mixed with pure water in the vat and allowed to 

 settle ; the remaining gluten is deposited as a grey slimy matter 

 above the starch, which is removed, and the starch washed 

 again till pure. For the fermentation, the action of a weak solu- 

 tion of caustic alkali has lately been substituted, by which the 

 gluten of flour is dissolved and the starch left. Mr. O. Jones 

 employs a ley containing 200 grains of caustic soda in one gallon 

 of water. A ley containing 400 grains of soda causes the starch 

 to gelatinize ; by that quantity of ley, one pound of excellent 

 starch is obtained from flour of rice, allowed to digest in it in the 

 cold for forty-eight hours. 



Arrow root is the starch from the root of the marantha arun- 

 dinacea. It is not accompanied by any odoriferous principle, and 

 has therefore no smell when boiled with water, in which respect 

 it resembles potato starch washed with alcohol. Sago is 

 derived from the pith of true palms of the genus Sagus ; tapioca 

 or cassava, from an American plant, the iatropha manihot, of 

 which the milky juice, itself poisonous, deposits when diffused 

 through water a harmless starch. The peculiar appearance and 

 solubility in cold water of sago and tapioca arise from the starch 

 being exposed while humid to a temperature above 140, so that 

 it is dried in the gelatinous condition and not in the original 

 grains. 



Starch or fecula may be purified from adhering gluten by 

 maceration in diluted acetic acid, or by means of a cold and 

 dilute solution of alkali. The starch of commerce is perfectly 

 white, and in small columns formed by the contraction of the 

 humid mass of starch in drying, which are easily reduced to a 

 fine powder. It emits a particular sound when pressed between 

 the fingers, its density is 1.53. The other characters which 

 fecula exhibits are complete insolubility in cold water and in 



