CHEMISTRY. 



Chemical 

 Examina- 

 tion of 

 Nature. 



hj proper- 

 ties. 



edulcorated with water, is dried with a moderate heat. 

 During the drying, it usually splits into columnar mas- 

 ses, which have a considerable degree of regularity. 



Starch was well known to the ancients. According 

 to Pliny, the method of manufacturing it was discovered 

 by the inhabitants of Chios. 



Starch has a fine white colour, and is usually concre- 

 ted in four-sided prisms. It has scarcely any smell, and 

 very little taste. When kept dry, it continues for a long 

 time uninjured, though exposed to the air. 



It does not dissolve in cold water, but very soon falls 

 to powder, and forms a kind of emulsion. It dissolves 

 in boiling water, and forma a kind of jelly, which may 

 be diffused through boiling water ; but when the mix- 

 ture is allowed to stand a sufficient time, the starch slow- 

 ly precipitates to the bottom. The subsidence takes place 

 even when 90 parts of water are employed to dissolve one 

 ef starch ; but, in that case, at least a month elapses be- 

 fore the starch begins to precipitate. The solution is 

 glutinous in proportion to the quantity of starch. Linen 

 dipt into it and suddenly dried, acquires a considerable 

 degree of stiffness. When the solution is evaporated to 

 dryness, a brittle opake mass is obtained, differing in ap- 

 pearance from common starch, but exhibiting nearly the 

 Same properties with re-agents. Hence the apparent 

 difference is probably owing to a portion of water re- 

 maining united to the boiled starch. When the solution 

 of starch is left exposed to damp air, it soon loses its 

 consistency, acquires an acid taste, and becomes mouldy 

 on the surface. 



Starch does not dissolve, nor even fall to powder in al- 

 cohol. Neither does it dissolve in ether. 



Neither oxygen gas nor the simple combustibles have 

 any marked action on starch. The metals and their ox- 

 ides have little affinity for it. Acetate of lead throws it 

 down from water, but the superacetate has no effect upon 

 it. According to Dr Bostock, it is precipitated also by 

 oxymuriate of tin ; but in the trials made by the writer 

 of this article, he obtained no precipitate with that salt 

 in a decoction containing one- ninetieth of its weight of 

 starch. No other metallic salt tried produced a precipi- 

 tate in this decoction. 



Neither lime nor strontian water precipitate the decoc- 

 tion of starch ; but barytes water throws down a copious 

 white flaky precipitate. It is dissolved by muriatic acid, 

 but appears again on standing, unless a considerable ex- 

 cess of acid be added. Neither muriate of barytes nor 

 silicated potash occasion any precipitate in the decoction 

 of starch. 



When starch is triturated in a hot infusion of nutgalls, 

 a complete solution is effected. This solution is trans- 

 parent, and rather lighter coloured than the infusion of 

 nutgalls employed. When this solution cools, it becomes 

 opake, and a copious curdy precipitate falls. A heat of 

 120 re-dissolves this precipitate, and renders the solu- 

 tion transparent, but it is deposited again as the liquid 

 cooli. This property is characteristic of starch. The 

 infusion of nutgalls throws it down from every solution, 

 but the precipitate is re-dissolved by heating the liquid 

 to 120. The precipitate is a c impound of tannin and 

 starch, and is least eoluble when composed of about three 

 parts starch, and two parts tannin. It has a brownish 

 yellow colour, i* semi -transparent, has an astringent taste, 

 and feels glutinous between the teeth like gum. 



When potash i triturated with starch, and a little wa 

 ter added, the whole assumes, on standing, the appear- 

 ance of a semi transparent jelly. On adding water, an 

 pal c .loured solution is obtained, from which the starch 

 is readily thrown down by an acid. When muriatic acid 



is employed, a peculiar aromatic odour is perceived. The 

 decoction of starch is neither altered by potash, carbo- 

 nate of potash, nor ammonia. 



When starch is thrown into any of the mineral acids, 

 at first no apparent change is visible ; but, if an attempt 

 is made to reduce the larger pieces, while in acids, to 

 powder, they resist it, and feel exceedingly to'.igh and 

 adhesive. Sulphuric acid dissolves it slowly, and at the 

 same time a smell of sulphuric acid is emitted, and such a 

 quantity of charcoal evolved, that the vessel may be in- 

 verted without spilling any of the mixture. Diluted 

 sulphuric acid dissolves starch when assisted by heat, and 

 the st.arch may be again precipitated by means of alco- 

 hol. 



Diluted nitric acid slowly dissolves starch ; the acid ac- 

 quires a green colour, and a small portion of white mat- 

 ter swims on the surface, on which the acid does not act. 

 Alcohol throws down the starch from this solution. 

 Concentrated nitric acid dissolves starch pretty rapidly, 

 assuming a green colour, and emitting nitrous gas. The 

 solution is never complete, nor do any crystals of oxalic 

 acid appear unless heat be applied. In this respect starch 

 differs from sugar, which yields oxalic acid even at the 

 temperature of the atmosphere. When heat is applied 

 to the solution of starch in nitric acid, both oxalic and 

 malic acids are formed, but the undissulved substance 

 still remains. When separated by filtration, and after- 

 wards edulcorated, this substance has the appearance of 

 a thick oil not unlike tallow ; but it dissolves readily in 

 alcohol. When distilled it yields acetic acid and an oil, 

 having the sm- 11 and consistence of tallow. 



Strong muriatic acid dissolves starch slowly and with- 

 out effervescence. When the starch does not exceed one- 

 twentieth of the acid, the solution is colourless and trans- 

 parent ; but if we continue to add starch, a brown colour 

 appears, and the acid loses a portion of its fluidity. Its 

 peculiar smell is destroyed, and replaced by the odour 

 which may be perceived in corn mills. Acetic acid docs 

 not dissolve starch. The action of the other acids has 

 not been tried. 



Alcohol separates starch in part from its decoction. 

 A solution of potash in alcohol occasions a copious 

 white precipitate, which is re-dissolved on adding a suf- 

 ficient quantity of water. A solution of sulphuret of 

 potash in alcohol occasions a flaky precipitate in the de- 

 coction of starch. This precipitate has sometimes a 

 orange colour. 



When starch is thrown upon a hot iron, it melts, 

 blackens, frothes, swells, and burns with a bright flame 

 like sugar, emitting at the same time a great deal of 

 smoke ; but it does not explode, nor has it the caromel 

 smell which distinguishes burning sugar. When distil- 

 led, it yields water, impregnated with an acid supposed to 

 be the pyromucous, a Tittle empyreumatic oil, and a 

 great deal of carbonic acid and heavy inflammable air. 

 The charcoal which it leaves burns easily when kindled 

 in the open air, and leaves very little ashes. According 

 to the experiments of Thenard and Gay-Lussac, it ia 

 composed of 



Oxygen 49.68 

 Catbon 43.55 

 Hydrogen 6.77 



100 



Starch is contained in a great variety of vegetable sub- 

 stances ; most commonly in their seeds or bulbous roots, 

 but sometimes also in other parts. All the different 

 sprcies of corn contain a gr at proportion of it. There 

 are obviously different varieties of starch, possessing dr- 



Compo.-,;- 

 tion. 



