152 CHYMISTRY APPIJED TO AGRICULTURE." 



The plants of southern climates, when transported to the 

 north, lose their perfume,- and the insipid vegetables of 

 Greenland acquire taste and smell when transplanted to the 

 gardens of the south of Europe. 



In the spring of the year, trees a^re full of juices, but 

 they yield at that time principally mucilage ; in autumn 

 they afford oil, starch, sugar, &c. Professor Plot remarks, 

 that in the year 1692, trees cut in the sap were devoured 

 by worms, and that the wood warped in drying and ac- 

 quired but little hardness. Julius Caesar was convinced of 

 this truth when he caused his vessels to be built of wood 

 cut in the spring. And Vitruvius advised that trees should 

 be cut down only at the close of winter, " when the power 

 of the cold shall have compressed and consolidated the 

 wood." 



Vegetable fibre burns in the open air with a yellow 

 flame, and disengages water and carbonic acid ; distilled 

 in close vessels it leaves a residuum of carbon : it is by 

 this process, that the charcoal used for most purposes is 

 procured. 



The most common method of procuring charcoal con- 

 sists in cutting the branches and young trunks of trees into 

 billets of about three feet in length, and two inches in 

 diameter ; a portion of the prepared wood is laid upon the 

 ground in parallel lines, and the remainder is piled upon it 

 in a hemispherical form, to the height of six or eight feet ; 

 the surface is then covered over with earth or sods of grass, 

 and the pile set on fire by means of a flue in the centre. 

 In a short time the whole mass is heated through, and 

 water, carbonic acid, and volatile oil are thrown out with 

 the smoke; this will cease to appear when the wood is 

 reduced to a black, sonorous body, and the pile may then 

 be opened. 



This process is very faulty, as in it a great part of the 

 wood intended to be carbonized is burned up, and because 

 great skill is requisite for carbonizing the mass uniformly. 



Wood reduced to charcoal yields from -j^^^^ to -j?^%^ of its 

 weight, according to the nature of the wood, and the care 

 with which the operation has been performed. 



Different kinds of wood yield coal of very different 

 quality : the best coal is heavy and sonorous, and is pro- 

 duced from wood of very compact fibre. The heat it af- 

 fords is quick and strong, and its combustion, though vigor- 

 ous, lasts a long time. The charcoal of the green oak of 



