CAEBON AND ITS COMPOUNDS. 29 



42. Why Coal is called a Mineral. Coal being thus of 

 vegetable origin, and retaining the evidences of this in 

 its very texture, it might at first thought appear that it 

 could hardly be called a mineral. The reason that it is 

 proper to call it so I will point out. The carbon, which 

 is the chief component of all kinds of coal almost the 

 only component of one kind, the anthracite does not ex- 

 ist in the vegetable as carbon, but, chemically united with 

 oxygen and hydrogen r it forms woody fibre. It is just 

 as sulphur does not exist as sulphur in sulphate of lime 

 (gypsum), but as a part of a compound united chemical- 

 ly in it with oxygen and lime, as carbon in wood is united 

 chemically with oxygen and hydrogen. Now when wood 

 is made to produce coal a chemical change occurs, a real 

 decomposition is effected, so that carbon now appears in 

 its uncombined state. The form, indeed, of woody fibre 

 may remain, but it is no longer wood the compound of 

 carbon, oxygen, and hydrogen. These elements are sep- 

 arated from each other; and if they are combined, as may 

 be the case in bituminous coal, it is a recombination after 

 separation. A farther chemical change or decomposition 

 is produced when the coal is burned, all the carbon then 

 passing off by forming carbonic acid gas with the oxy- 

 gen of the air. The first process is as strictly and fully a 

 chemical change as the last, and it is by chemical changes 

 that minerals are produced. We have here a clear case 

 of the passage of an organized substance under the con- 

 trol of living agencies over into the mineral kingdom, 

 where chemical laws bear sway. 



43. Peat. In peat we have an example of imperfect 

 formation of coal, the approach to the completion of the 

 process being different in different cases. It accumulates 

 in swampy places, mostly from the growth of mosses of 

 one genus, Sphagnum. The roots continually die below 

 as the plant grows upward ; and as these roots, by the 

 partial decomposition under water, change into peat, a 

 bed of great thickness may after a time be formed. 



