218 SCIENCE OF AGRICULTURE. Part II. 



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 whicli 

 the pith contained, or the sago of the shops. 



1375. Salop is also a species of starch that is prepared, in the countries of the East, from the root of 

 the orchis morio, mascula, bifoho, and pyramidalis, and in the isle of Portland, from the arum maculatum. 

 So also is cassava, which is prepared from the root of jatropha manihot, a native of America, the ex- 

 pressed 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 ; and so also is sowans, which is prepared from the husk of oats, as obtained in the 

 process of grinding. , , 



1376. Starch may be extracted from a number of plants ; as arctium lappa, atropa belladonna, polygo- 

 num bistorta, bryonia alba, colchicum autumnale, spiraea filipendula, ranunculus bulbosus, scrophularia 

 nodosa, sambucus ebulus and nigra, orchis morio and mascula, imperatoria ostruthium, hyoscyamus 

 niger, rumex obtusifolius, acutus, and aquaticus, arum maculatum, iris pseudacorus and fcetidissima, 

 orobus tuberosus, bunium bulbocastanum. It is found also in the following seeds : wheat, barley, oats, 

 rice, maize, millet-seed, chestnut, horse-chestnut, peas, beans, acorns. 



1377. Starch is an extremely nutritive substance, and forms one of the principal ingredients in almost all 

 articles of vegetable food used, whether by man or the inferior animals. The latter feed u^wn 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, or confectionery. Its utility is also consider- 

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

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

 powder. 



1378. Gluten is that part of the paste formed from the flour of wheat that 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 color, without taste, but of a very peculiar smell. It is soluble in the acids and alkalies, but 

 insoluble in water and in alcohol. Gluten lias 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. 



1379. Gluten is one qf the most 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 capable of being used as a varnish, and a ground 

 for paint. 



1380. Albumen, which is a thick, glary, 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 an- 

 nounced 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. 



1381. Fibrina 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 elasticity. 

 A substance possessing the same properties has been detected by Vauquelin in the juice of the papaw- 

 tree, which is called vegetable fibrina. 



1382. 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 different species, of which the following are the most remarkable : 



\Z9,Z. Extract of catechu. This extract is obtained from an 13S5. Extract (f qiiinijuina. 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 quin- 



color 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 



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



iwrous charcoal. boUing water ; its color is brown, and its taste bitter. It is 



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



fusion of the dried leaves of cassia senna in alcohol. The color red powder ; and when dry it is black and brittle, breaking 



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



smell aromatic. It is precipitated from its solution by the 158C. Extract of.tqffrim. 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 odor, leaving which are almost wholly soluble in yiaXei, 

 Ijehind a spongy charcoal. 



1387. Extracts were formerly much employed in medicine; 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 colors 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. 



1388. Coloring matter. The beauty and variety of the coloring of vegetables, chemists have ascribed to 

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

 have accordingly endeavored 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 coloring matter seem to be as 

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

 tholet, Chaptal, and others. Its affinities to oxygen, alkalies, earths, metallic oxides, and cloths fabri- 

 cated, whether 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 ; 

 and hence wool and silk assume a deeper dye, and retain it longer than cotton or linen. Coloring matter 

 exhibits a great variety of different tints, as it occurs in different species of plants ; and as it combines 

 with oxygen, which it absorbs from the atmosphere, it assumes a deeper shade ; but it loses at the same 

 time a portion of its hydrogen, and becomes insoluble in water ; and thus it indicates its relation to ex- 

 tract. Fourcroy reduced colors to the four following sorts ; extractive colors, oxygenated colors, carbo- 

 nated colors, and hydrogenated colors ; the first being soluble in water, and requiring the aid of saline or 

 metallic mordants to fix them-upon cloth ; the second being insoluble in water, as altered by the absorp- 

 tion of oxygen, and requiring no mordant to fix them upon cloth ; the third containing in their compo- 

 sition a great proportion of carbon, but soluble in alkalies; and the fourth containing a great projwrtion 

 of resin, but soluble in oils and alcohol. But the simplest mode of arrangement is that by which the dif- 



