218 SCIENCE OF AGRICULTURE. Part II. 



when thrown upon red-hot iron, burns with a kind of explosion, and leaves scarcely any residuum behind. 

 It has been found, by the analysis of Gay Lussac and Thenard, to be composed of carbon 4355 ; oxygen 

 49"68 ; hydrogen 6-77 ; total 100. This result is not very \yidely different from that of the analysis of 

 sugar, into which, it seems, starch may be converted by diminishing the proportion of its carbon, and 

 increasing that of its oxygen and hydrogen. This change is exemplified in the case of the malting of 

 barley, which contains a great proportion of starch, and which absorbs during the process a quantity of 

 oxygen, and evolves a quantity of carbonic acid ; and accordingly part of it is converted into sugar. 

 Perhaps it is exemplified also in the case of the freezing of potatoes, which acquire in consequence a sweet 

 and sugary taste, and are known to contain a great deal of starch, which may be obtained as follows. Let 

 the potatoes be taken and grated down to a pulp, and the pulp placed upon a fine sieve, and water made 

 to pass through it : the water will be found to have carried off' with it an infinite number of particles, 

 which it will afterwards deposit in the form of a fine powder, separable by decantation ; which powder is 

 starch, possessing all the essential properties of wheaten starch. It may be obtained from the pith of 

 several species of palms growing in the Moluccas and several other East India islands, by the following 

 process : the stem, being first cut into pieces of five or six feet in length, is split longitudinally so as to 

 expose the pith, which is now taken out and pounded, and mixed with cold water, which, after being 

 well stirred up, deposits at length a sediment that is separated by decantation, and is the starch which 

 the pith contained, or the sago of the shops. 



1401. Salop is also a species of starch that is prepared, in the countries of the East, from the root of the 

 O'rchis morio, mascula, bifblia, and pyramid^is ; and, in tlie Isle of Portland, from the ^"^rum maculktum. 

 So also is cassava, which is prepared from the root of Jdnipha Mdnihot, a native of America, the 

 expressed juice of which is a deadly poison used by the Indians to poison their arrows ; but the sediment 

 which it deposits is a starch that is manufactured into bread, retaining nothing of the deleterious pro- 

 perty of the juice. So also is sowans, which is prepared from the husk of oats, as obtained in the process 

 of grinding. 



1402. Starch may be extracted from a number of plants ; as ^'rctium Lappa, A'tropa Belladdnna, Polygo- 

 num bisturta, ^rybnia alba, Colchicum autumnale, Spira'^a Filipt^ndula, JTanunculus bulbbsus, Scrophu- 

 Ikria nodbsa, Sambticus JS'bulus and nigra, O'rchis mbrio and mascula, Imperatbria Ostruthium, 

 /fyoscyamus nlger, ^dmex obstusifolius, actitus, and aquaticus, /IVum maculktum, i'ris Pseudacorus and 

 fcetidissima, O'robus tuberusus, and .Banium Bulbocastanum. It is found also in the following seeds : 

 wheat, barley, oats, rice, maize, millet seed, chestnut, horsechcstnut, peas, beans, and acorns. 



1403. Starch t's an extremely nutritive substance, and forms one of the principal ingredients in almost all 

 articles of vegetable food used by. man or by the inferior animals. The latter feed upon it in the 

 state in which nature presents it ; but man prepares and purifies it so as to render it pleasing to his taste, 

 and uses it under the various modifications of bread, pastry, and confectionary. Its utility is also consider- 

 able in medicine and in the arts ; in the preparation of anodyne and strengthening medicaments ; in 

 the composition of cements ; in the clearing and stiffening of linen j and in the manufacture of hair- 

 powder. 



1404. Gluten is that part of the paste formed from the flour of wheat, which remains unaffected by the 

 water, after all the starch contained in it has been washed off It is a tough and elastic substance, of a 

 dull white colour, without taste, but of a very peculiar smell. It is soluble in the acids and alkalies, but 

 insoluble in water and in alcohol. Gluten has been detected, under one modification or other, in a very 

 considerable number of vegetables or vegetable substances, as well as in the flour of wheat. 



1405. Gluten is one of the ?nost important of all vegetable substances, as being the principle that renders 

 the flour of wheat so fit for forming bread, by its occasioning the panary fermentation, and making the 

 bread light and porous. It is used also as a cement, and is capable of being used as a varnish and a ground 

 for paint. 



1406. Albumen, which is a thick, glairy, and tasteless fluid, resembling the white of an unboiled egg, is 

 a substance that has been but lately proved to exist in the vegetable kingdom. Its existence was first 

 announced by Fourcroy, and finally demonstrated by the experiments of Vauquelin on the dried juice of 

 the papaw tree. It is nearly related to animal gluten. 



1407. Fibrine is a peculiar substance which chemists extract from the blood and muscles of animals. This 

 substance constitutes the fibrous parts of the muscles, and resembles gluten in its appearance and elasti- 

 city. A substance possessing the same properties has been detected by Vauquelin in the juice of the 

 papaw tree, which is called vegetable fibrine. 



1408. Extract. When vegetable substances are macerated in water, a considerable portion of them is 

 dissolved ; and if the water is again evaporated, the substance held in solution may be obtained in a sepa- 

 rate state. This substance is denominated extract. But it is evident that extract thus obtained will not 

 be precisely the same principle in every different plant, but will vary in its character according to the 

 species producing it, or the soil in which the plant has grown, or some other accidental cause. Its dis- 

 tinguishing properties are the following : It is soluble in water as it is obtained from the vegetable, but 

 becomes afterwards insoluble in consequence of the absorption of oxygen from the atmosphere It is solu- 

 ble in alcohol ; and it unites with alkalies, and forms compounds which are soluble in water. When 

 distilled it yields an acid fluid impregnated with ammonia, and seems to be composed principally of hydro- 

 gen, oxygen, carbon, and a little nitrogen. Extract, or the extractive principle, is found in a greater 

 or less proportion in almost all plants whatever, and is very generally an ingredient of the sap and bark, 

 particularly in barks of an astringent taste ; but still it is not exactly the same in all individual plants, 

 even when separated as much as possible from extraneous substances. It may therefore be regarded as 

 constituting several species, of which the following are the most remarkable ; 



1409. Extract of caiechu. This extract is obtained from an 1411. Extract nf quinquina. This extract -was obtained by 

 infusion of the wood or powder of catechu in cold water. Its Fourcroy, by evaporating a decoction of the bark of the (juin- 

 colour is pale brown ; and its taste slightly astringent. It is quina of St. Domingo in water, and again dissolving it in 

 precipitated from its solution by nitrate of lead, and yields by alcohol, which finally deposited by evaporation the peculiar 

 disUUation carbonic and carburetted hydrogen gas, leaving a extractive. It is insoluble in cold water, but very soluble in 

 porous charcoal. boiling water; its colour i brown, and its taste bitter. It is 



1410. Extract of senna. This extract is obtained from an in- precipitattd from its solution by lime water, in the form of a 

 fusion of the dried leaves of Cdssia S^nna in alcohol. The co- red powder ; and when dry it is black and brittle, breaking 

 lour of the infusion is brownish, the taste slightly bitter, and with a polished fracture. 



the smell aromatic. It is precipitated from its solution by the 1412. Extract of saffron. This extract is obtained in great 



muriatic and oxymuriatic acids ; and, when thrown on burning abundance from the summits of the pistils of Crocus sativus, 

 coals, consumes with a thick smoke and aromatic odour, leaving which are almost wholly soluble in water. 



behind a spongy charcoal. 



1413. Extracts were formerly much employed in medicifie ; though their efficacy seems to have been 

 overrated. But a circumstance of much more importance to society is that of their utility in the art of 

 dyeing. By far the greater part of colours used in dyeing are obtained from vegetable extracts, which 

 have a strong affinity to the fibres of cotton or linen, with which they enter into a combination that is 

 rendered still stronger by the intervention of mordants. 



1414. Colouring matter. The beauty and variety of the colouring of vegetables, chemists have ascribed to 

 the modifications of a peculiar substance which they denominate the colouring principle, and which they 

 have accordingly endeavoured to isolate and extract ; first, by means of maceration or boiling in water, 

 and then by precipitating it from its solution. The chemical properties of colouring matter seem to be as 

 yet but imperfectly known, though they have been considerably elucidated by the investigations of 

 Berthollet, Chaptal, and others. Its affinities to oxygen, alkalies, earths, metallic oxides, and cloths 

 fabricated of animal or vegetable substances, such as wool or flax, seem to be among its most striking 



. characteristics. But its affinity to animal substances is stronger than its affinity to vegetable substances ; 



