VEGETABLE CHEMISTRY. 



791 



with an acid, with which they form a salt more or 

 less soluble in water. These alkalies are, for the 

 most part, very insoluble in water, and of sparing 

 solubility in cold alcohol ; but they are all readily 

 dissolved by that fluid at a boiling temperature, 

 being deposited from the solution, commonly in the 

 form of crystals, on cooling. Most of the salts are 

 far more soluble in water than the alkalies them- 

 selves, and several of them are remarkable for their 

 solubility. As the vegetable alkalies agree in 

 several of their leading chemical properties, the 

 mode of preparing one of them admits of being ap- 

 plied, with slight variation, to all. The general 

 method is as follows : The substance containing 

 the alkaline principle is digested, or, more com- 

 monly, macerated, in a large quantity of water, 

 which dissolves the salt, the base of which is the 

 vegetable alkali. On adding some more powerful 

 saleable base, such as potassa or ammonia, or boil- 

 ing the solution for a few moments with lime or 

 pure magnesia, the vegetable alkali is separated 

 from its acid ; and being, in that state, insoluble in 

 water, may be collected on a filter, and washed. 

 To purify it from certain oleaginous, resinous sub- 

 stances and colouring matters, it is mixed with a 

 little animal charcoal and dissolved in boiling alco- 

 hol. This solution is filtered while hot, and eva- 

 porated to dryness, which affords the alkali in a 

 state of perfect purity. Upwards of twenty of 

 these bodies have already been investigated. The 

 following are the names of those which are the 

 most important : morphia, cinchonia, quinia, strych- 

 nia, brucia, veratria and sanguinaria. 



3. Oils are characterized by a peculiar unctuous 

 feel, by inflammability, and by insolubility in water. 

 They are divided into fixed and volatile oils, the 

 former of which are comparatively fixed in the fire, 

 and therefore impart a permanent stain to paper ; 

 while the latter, owing to their volatility, produce 

 a stain which disappears by gentle heat. See Oils, 

 and Essential Oils. 



4. Resins are the inspissated juices of plants, 

 and commonly occur either pure or in combination 

 with an essential oil. They are solid at common 

 temperatures, brittle, inodorous and insipid. They 

 are non-conductors of electricity, and, when rubbed, 

 become negatively electric. They are generally of a 

 yellow colour and semi-transparent. They are rnelt- 

 ed by the application of heat, and, by a still higher 

 temperature, are decomposed. In close vessels, 

 they yield empyreumatic oil, and a large quantity 

 of carbureted hydrogen. In the open air, they burn 

 with a yellow flame and much smoke, being resolved 

 into carbonic acid and water. Resins are dissolved 

 by alcohol, ether and the essential oils; and the 

 alcoholic and ethereal solutions are precipitated by 

 water, a fluid in which they are quite insoluble. 

 Their best solvent is pure potash and soda; and 

 Ihey are soluble in the alkaline carbonates by the 

 nid of heat. The product is, in each case, a soapy 

 compound, which is decomposed by an acid. The 

 most important are described under their respective 

 names, in this work. Alcohol is the intoxicating 

 ingredient of all spirituous and vinous liquors. It 

 does not exist ready formed in plants, but is a pro- 

 duct of the vinous fermentation. (See Fermenta- 

 tion.) Ether is a general term applied to several 

 compounds produced from the action of acids on 

 alcohol. 



4. Those substances in which the oxygen and 

 hydrogen are in the exact proportion for forming 

 water, are sugar, starch, gum, and lignin, all of 



which have been described, except the last. Lignin 

 forms the fibrous structure of vegetable substances, 

 and is the most abundant principle in plants. The 

 different kinds of wood contain about 96 per cent, 

 of lignin. It is prepared by digesting the sawings 

 of any kind of wood successively in alcohol, water 

 and dilute muriatic acid, until all the substances 

 soluble in these menstrua are removed. It has 

 neither taste nor odour, undergoes no change by 

 keeping, and is insoluble in alcohol, water and the 

 dilute acids. When the woody fibre is heated in 

 close vessels, it yields a large quantity of impure 

 acetic acid and charcoal. It consists of carbon 

 51-43, oxygen 42-73, and hydrogen 5-82. 



5. Substances not belonging to either of the pre- 

 ceding sections. The most important of these are 

 colouring matter, tannin, vegetable albumen, gluten, 

 yeast, asparagin, caffein, cathartin, piperin, bitter 

 principle., and extractive matter. 



The Chemical Phenomena of Germination and 

 Vegetation. Germination is the process by which 

 a new plant originates from seed. A seed consists 

 essentially of two parts the germ of the future 

 plant, endowed with a principle of vitality, and the 

 cotyledons, or seed-lobes, both of which are en- 

 veloped in a common covering of cuticle. In the 

 germ, two parts the radicle and the plumule 

 may be distinguished, the former of which is des- 

 tined to descend into the earth and constitute the 

 root, the latter to rise into the air and form the 

 stem of the plant. The office of the seed-lobes is 

 to afford nourishment to the young plant, until its 

 organization is so far advanced, that it may draw 

 materials for its growth from extraneous sources. 

 For this reason, seeds are composed of highly nu- 

 tritious ingredients. The chief constituent of most 

 of them is starch, in addition to which they fre- 

 quently contain gluten, gum, vegetable albumen 

 or curd, and sugar. The conditions necessary to 

 germination are three-fold, viz. moisture, a certain 

 temperature, and the presence of oxygen gas. The 

 necessity of moisture to this process has been proved 

 by extensive observation. A certain degree of 

 warmth is not less essential. Germination cannot 

 take place at 32 Fahr. ; and a strong heat, such 

 as that of boiling water, prevents it altogether, by 

 depriving the germ of the vital principle. The 

 most favourable temperature ranges from 60 to 

 80, the precise degree varying with the nature of 

 the plant a circumstance that accounts for the 

 difference in the season of the year at which dif- 

 ferent seeds begin to germinate. The presence of 

 air is indispensable for the germination of seeds ; 

 but the influence of light, which is so favourable to 

 all the subsequent stages of vegetation, is injurious 

 to the process of germination. The operation of 

 malting barley, in which the grain is made to ger- 

 minate by exposure to warmth, air and humidity, 

 affords the best means of studying the phenomena 

 of germination. In preparing malt, the grain passes 

 through four stages, called steeping, couching, floor- 

 ing and kiln-drying. In the first, it is steeped in 

 water for about two days, when it absorbs moisture, 

 softens, and swell? considerably. It is then re- 

 moved to the couch fra'me, where it is laid in heaps, 

 thirty inches in depth, from twenty-six to thirty 

 hours. In this situation, the grain becomes warm, 

 and acquires a disposition to germinate ; but as the 

 temperature, in such large heaps, would rise very 

 unequally, and germination consequently be rapid 

 in some portions and slow in others, the process of 

 flooring is employed. This consists in laying the 



