cir SCIENCE OF AGRICULTURE. Part II. 



when thrown upon red-hot Iron, bunu with ■ kind of explosion, and leave* scarcely any residuum behind, 

 It haa been round, bj the analj lit ol Qaj Lussac and Tnenard, to be composed of carbon 43 55 ; oxygen 

 4!i r,s ; hydrogen '.",7, total 100. This result is not very wldelj different from that of the analysis ol 

 sli^: ir, into which, it seems, starch may be converted by diminishing the proportion of its carbon, and 

 increasing thai ol Its oxygen and hydrogen. This change is exemplified In the case of the malting of 

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



i'v\m, and evolves a quantity of carl c acid, and accordingly part of it is converted into sugar. 



Perhaps It is exemplified also in the case ol tin- freezing of potatoes, which acquire in consequence a sweet 

 and sugary taste, and arc- known to contain a (.Teat deal of starch, which ma] in- obtained as follows. Let 



tin' potatoes In- takm anil grated down to a pulp, and the pulp placed upon a fine sieve, and water made 



to pass through it : the water a 111 be found to have earned off with it an infinite number of particles, 

 which it w ill afterwards deposit in the form ol a due 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 ..I palm- growing in tin- Moluccas and several other Baal India isl mils, by the following 

 process : the stem, being ( i r - 1 cut into puces 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 com water, which, after being 



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

 the pith contained, or the sago ol the shops. 



1401. Sii/o/i is also ,; species qf starch that is prepared, in the countries of the East, from the root of the 

 O'rchis in. no, m iscula, hi folia', and pyramidalis ; and, in the isle of Portland, from the .-Prum maculatum. 

 So also is cassava, which is prepared from the root of Jtinip/ia Mdnihot, a native of America, the 



expn I 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. 



1 U 12. Starch mm/ be extracted from a number of plants ; as /Trctium Lappa, A'tropn Belladonna, Polygo- 

 num bistorts, .Bryonia alba, Colchlcurn autumnale, .s'pira?\i Filipendula, SanAnculus bulbbsus, Scrophu- 

 laria nodosa, SambdCUS £'bulus and nigra, O'rchis morio and mascula, Iinpcratbria Ostruthium, 

 //yoscvainus nlger, /iiimex obstusifolius, acutus, and aquaticus, .Prum macul&tuin, Pris Pseudacorus and 

 fietidissima, O'robus tuberc'isus, and 7?unium Kulbocastanuin. It is found also in the following seeds: 

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



1 103. Starch is an extreme/;/ 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 purities 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 ; and in the manufacture of hair, 

 powder. . 



14<>4. 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 most important of all vegetable substances, as being the principle that raiders 

 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. . 



140ii. 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. 



14b7. 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 giuten 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 everv 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 catrchu. This extract is obtained from an 1411. Extract nf quinquina. Tliis extract was obtained by 

 infusion of the wood or powder of catechu in cold water. Its Fourcrov, hy evaporating a decoction of the bark of the ouin- 

 rolouris p tic- brown ; and its taste -.lightly astringent. It is quina of St. Domingo in water, and again dissolving it in 

 precipitated from its solution bj nitrate of lead, and yields hy alcohol, whic-h finally deposited by evaporation the peculiar 

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

 porous charcoal. boiling water; its co'our \i brown, and its taste bitter. It is 



1 110. t'rtr.ut of senna. This extract is obtained from an in- precipitated from its solution by ime water, in the form of a 



fusion of the dried leaves ..t' ' i.si.i s „,„/ in alcohol. The co- red powder ; and when dry it is black and brittle, breaking 



lour of the infusion is lirnnni.li. the t.csic- slight!} bitter, and Willi a polished fracture. 



the smell aromatic. It is precipitated from its solution by the 1-11*2. Extract of siijl'rou. This extract is obtained in great 



muriatic and oxyrour! ilii 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. 



141:!. 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 ot 

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

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

 rendered still stronger by the intervention of mordants. 



1414. Colouring mutter. The beauty and variety of the colouring ofvegctables, chemists have ascribed to 

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

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

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

 vet 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, liut its alliuitv to animal substances is stronger than its affinity to vegetable substances; 



