400 



The Economic Production of Artificial Heat. 



already in combination with the supporter. One pound of or- 

 dinary wood, in a proper condition for burning, will raise about 

 twenty-six pounds of water from 0° to 212°, or will evaporate 

 four and three-quarter pounds of boiling water ; but much de- 

 pends on its hygrometric state. 



Peat. — From the comparatively limited supply of this sub- 

 stance, and other circumstances, it might almost be neglected 

 in treating of fuels. Its efficiency depends, in a great degree, 

 on its compactness and its freedom from earthy matters. The 

 former is sometimes artificially increased by pressure : but its 

 elasticity is an obstacle to its compression, and the cost of con- 

 densing it is considerable ; if, however, its density is sufficient, 

 it is applicable to many important processes. The qualities of 

 peat are so variable, that while one pound of some kinds will 

 raise sixty pounds of water from the freezing to the boiling 

 point, one pound of other kinds will not raise twenty pounds of 

 water through the same number of degrees ; and its calorific 

 power when dry is only about half that of the same weight of coal. 

 But much depends on the locality in which it is obtained : good 

 Irish peat is twice as effective as the best kinds found in France. 



Coal. — Notwithstanding the enormous quantities of coal 

 with which this country is so happily furnished, the period at 

 which it superseded wood is not very remote. It is universally 

 admitted to be of vegetable origin, but the forms of vegetation 

 of which it consists are so imperfectly known, that they afford 

 little information as to the state of the earth at the time they 

 were produced. In peat, the vegetable matter exists in various 

 stages of decomposition : lignite is evidently the carbonaceous 

 residue of forest- trees ; brown coal is vegetable matter in a 

 state intermediate between that of wood and bituminous coal ; 

 semi-bituminous, or " steam ccal," is that which is in a state 

 intermediate between bituminous coal and anthracite ; and the 

 latter is bituminous coal from which the gaseous constituents 

 have been expelled, most probably by heat, so that many spe- 

 cimens of it contain only a small amount of oxygen, and little 

 or no hydrogen. The following are, on an average, the chief 

 constituents of the substances just mentioned : — 





Carbon. 



Hydrogen. 



Oxygen. 



Nitrogen. 





4889 

 5064 

 62-80 

 69-74. 

 8160 

 8557 

 89-21 



607 

 6 03 

 5-03 

 7-07 

 5-27 

 464 

 2-48 



43-11 



42-05 

 23-27 

 9-24 

 7-91 

 218 

 0-20 



93? 

 1-28 S 



o-oo 



0-14 

 0-39 

 103 

 017 



| Oak 



Lignite 



Brown Coal 



Bituminous Coal 



Steam Coal 



Anthracite 





