&amp;gt;... V. 



60 ELEMENTS OP PLANTS. 



without any immediate connection with the earth, and 

 drink in all their food from the air. 



209. The charcoal in plants is never found perfectly 

 pure. Diamond is pure carbon. In plants it is always 

 combined with something else. By charring, that is, 

 exposing wood or other vegetable substance to great heat, 

 out of the reach of the open air, all the atmospheric 

 portions are consumed, or, to speak more properly, turned 

 into vapor and gases, and driven off, and a perfect skeleton 

 of charcoal, showing all the minutest parts of the structure 

 of the plant, is left. 



210. In peat, which is the woody substance often found 

 under the surface in swamps, and also in anthracite and 

 bituminous coal, which arc the remains of the vegetation 

 of former ages, every thing in the structure of the plants, 

 of which these substances are formed, is often so com 

 pletely retained, that from them the family, and even the 

 genus and species of the plant may be ascertained. 



211. By the process of charring, every thing except 

 the carbon is not consumed. Indeed nothing is consumed ; 

 but those portions capable of assuming a gaseous form 

 are driven off. By carefully burning, in air, the charcoal 

 left, the carbon combines with the oxygen of the air and 

 flies off in the state of invisible carbonic acid, a portion 

 of water which has still adhered to the charcoal is turned 

 into vapor, and a greater or less amount of ashes is left. 



212. All those elements which thus assume a gaseous 

 form and fly off into the atmosphere, as smoke, vapor or 

 gas, in these two kinds of burning or combustion, are 

 often called for that reason, the combustible, or, more 

 properly, the atmospheric elements. They are oxygen, 

 hydrogen, carbon, and nitrogen, and their compounds, 



