GELATINOUS STARCH OR AMIDIN. 739 



alcohol, but resolving itself in boiling water into a mucilaginous 

 liquid, which forms a jelly on cooling. This when suddenly 

 dried upon linen imparts considerable stiffness to it. Dilute 

 acids dissolve starch, and form a transparent and highly fluid 

 liquid. When this solution is boiled for a long time, the starch 

 is first converted into a body having the properties of gum, and 

 afterwards into starch sugar. Nitric acid with the assistance of 

 heat converts starch into oxalic and malic acids, without pro- 

 ducing a trace of mucic acid. Starch is also soluble in alkalies ; 

 when brayed with a concentrated solution of hydrate of potash, 

 it forms a transparent gelatinous compound soluble in alcohol 

 and water, from which the starch is precipitated by acids. Starch 

 is precipitated from solution by lime water and hydrate of barytes, 

 and by sub-acetate of lead containing ammonia, forming insoluble 

 compounds with lime, barytes and oxide of lead. A solution 

 of starch is also coagulated by borax, which combines with and 

 precipitates the starch, but not by boracic acid. Starch is pre- 

 cipitated by an infusion of gallnuts. It forms a blue insoluble 

 compound with iodine. 



Gelatinous starch or amidin. In this state starch appears to 

 retain a portion of its organisation or structure, upon which 

 some of its properties depend, and which is the cause of the 

 difference in properties of the varieties of starch, containing 

 the same chemical principle. When grains of fecula are 

 rubbed in a mortar with sand, their coating is broken and they 

 form a greyish white powder, which when mixed with a little 

 cold water immediately expands and forms a transparent jelly. 

 If the uninjured grains be thrown into water above 140, they 

 imbibe water, swell and burst their envelopes, which have a 

 certain degree of elasticity, and undergo the same change. But 

 the gelatinous starch has imbibed water like a sponge, without 

 being dissolved and when placed upon several folds of blotting 

 paper imparts to the latter its moisture, arid dries up into a 

 mass resembling horn, which exhibits again the same phenomena, 

 when after being reduced to powder it is treated with boiling 

 water. A portion of the gelatinous starch, however, appears 

 to be dissolved by a large quantity of cold water, about ^th of 

 the starch, when the bruised grains are diffused through 100 

 times their weight of cold water, and the whole of it when 

 gelatinous starch is boiled with 40 or 50 parts of water ; for the 

 mucilaginous liquid passes through a double paper filter and no 



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