152 



IIISTOKY OF THE VEGETABLE KINGDOM. 



gitudinal threads, Y.liich are divisible into otliers 

 still smaller. It is somewhat transparent, is 

 without taste or smell, and is not altered by ex- 

 posure to the atmosphere. It is insoluble in 

 water and alcohol ; but the fixed alkalies decom- 

 pose it with the assistance of heat. When 

 iieated in the open air it blackens without melt- 

 ing or frothing, and exhales a thick smoke and 

 pungent odour, leaving a charcoal that retains 

 the form of the original mass. When distilled 

 in a retort, it yields an empyreumatic oil, car- 

 buretted hydrogen gas, carbonic acid, and a por- 

 tion of ammonia. One hundred parts of the 

 woody fibre of oak yielded, according to the 

 analysis of Gay Lussac and Thenard, 



Carbon, 

 Oxygen, 

 Hydrogen, 



£2,53 



41.78 



£.60 



Charcoal. When wood is covered up from 

 the full action of the atmosphere, and burnt with 

 a smothered flame, the volatile parts are driven 

 off by the heat, and there remains behind a sub- 

 stance exhibiting the exact form, and even the 

 several layers, of the original mass. This pro- 

 cess is denominated charring, and the product is 

 charcoal. As it is the woody film alone which 

 resists the action of heat, while the other parts 

 of the plant are dissipated, it is plain that char- 

 coal must be the residuum of woody fibre, and 

 that the quantity of the one must depend upon 

 the quantity of the other, if they are not rather 

 to be considered as the same. Charcoal may be 

 obtained from almost all parts of the plant, whe- 

 ther solid or fluid, and it is rendered perceptible 

 by means of combustion. It often escapes, how- 

 ever, during this process, under the form of car- 

 bonic acid, of which it constitutes one of the 

 elements. From a variety of experiments made 

 on different plants, and on their dififerent parts, 

 it appears that the green parts contain a greater 

 proportion of charcoal than the rest; but this 

 proportion is found to diminish in autumn, when 

 ' the green parts begin to be deprived of their glu- 

 tinous and extractive juice. The wood contains 

 more charcoal than the alburnum — the bark 

 more than both ; but this last result is not con- 

 stant in all plants, because the bark is not a ho- 

 mogeneous substance, the outer parts being af- 

 fected by the air, and the inner parts not. The 

 wood of the quercws suher, separated from the 

 alburnum, yielded, from a hundred parts of its 

 dry substance, 19.75 of charcoal, the alburnum 

 17.6, the bark 26, leaves gathered in May, 80, in 

 September, 26. But the quantity of charcoal 

 differs also in different plants, as well as in dif- 

 ferent parts of the same. In the plants exa- 

 mined by Proust, the proportion was found to 

 be as follows, the quantity of wood charred being 

 represented by unity : — 



Charcoal is insoluble in water, of which, how- 

 ever, it absorbs a portion when newly made, as 

 also of atmospheric air. It is incapable of putre- 

 faction. It is not altered by the most violent 

 heat that can be applied, if all air and moisture 

 are excluded ; but when heated to about 800°, 

 it burns in atmospheric air or oxygen gas, and 

 if pure, without having any residuum. It is 

 regarded by chemists as being a triple compound, 

 of which the ingredients are carbon, hydrogen, 

 and oxygen. 



Charcoal is of great utility, both to the che- 

 mist and artist, as a fuel for heating furnaces, as 

 well as for a variety of other purposes. It is an 

 excellent filter for purifying water. It is a very 

 good tooth powder, and is an indispensable in- 

 gredient in the manufacture of gunpowder. 



The Sap. If a branch of a vine is cut asun- 

 der early in the spring, before the leaves have 

 begun to expand, a clear and colourless fluid will 

 issue from the wound, which gardeners denomi- 

 nate the tears of the vine. It is merely, how- 

 ever, the ascending sap, and may be procured 

 from almost any other plant by the same or simi- 

 lar means, and at the same season, but particu- 

 larly from the maple, birch, and walnut tree, by 

 boring a hole in the trunk. A small branch of 

 a vine has been known to yield from twelve to 

 sixteen ounces in the space of twenty-four hours. 

 A maple tree of ordinary size yields about two 

 hundred pints in a season, as has been already 

 stated ; and a birch tree has been known to yield 

 in the bleeding season, a quantity equal to its 

 own weight. The taste of this fluid is generally 

 insipid, but sometimes it is slightly saline, and 

 sometimes agreeably sweet, as in the case of the 

 birch tree. If it is agitated but slightly a froth 

 is formed on the surface ; and if it is kept for 

 any length of time in a close vessel, it ferments 

 and effervesces spontaneously, and at length bo- 

 comes strongly acid, assuming a bluish colour 

 and a turbid appearance. At last it deposits a 

 sediment, and resumes its transparency, but 

 forms, at the same time, a thin and mouldy pel- 

 licle on the surface. If exposed to the action of 

 heat it emits bubbles of carbonic acid gas, ex- 

 hales » strong odour of vinegar, and yields, by 

 distillation, carbonate of ammonia. Its charcoal 

 contains carbonate of potass, carbonate of lime, 

 and muriate and sulphate of potass. It com- 

 bines, in all proportions, with water, wliich di- 

 lutes and dissolves it when thick and viscid. 

 Strong acids deprive it of the carbonic and ace- 

 tous acid which it contains, and occasion the 



