492 



FUEL 



motion produced by the gravitating power of water, is really due to the emission of 

 heat from the sun. By the influence of Life vital force we may produce motion 

 and heat ; but here again, as life is dependent upon solar heat, we h;ivo to look to 

 the sun as its source. Electricity is another agent by means of which heat can lio 

 developed, but this power has a similar origin, in all probability, to heat itself. 

 Chemical action in a vast number of cases produces the disturbance which is manifested 

 as heat ; and the combustion of all kinds of fuel may be considered to be but examples 

 of chemical change. It is the operation especially of this source of heat, which wo 

 have to consider. 



All the substances used by man for the production of Fire are chiefly of vege- 

 table origin, as wood, peat, turf, and coal. Some few may possibly be derived from the 

 animal kingdom, as some of the native bitumens. But either vegetable or animal fuel 

 has originally gathered its heat from the sun in the process of growth and it has 

 held that heat stored until a peculiar disturbance has liberated it for the use of man. 



Numerous excellent experiments have been made for the purpose of determining with 

 exactness the heating values of fuels of different kinds. Lavoisier and Laplace, in 

 an extensive examination carried out by them, used their well-known Calorimeter, by 

 which they determined the value of the heat by the quantity of ice melted in a given 

 time. Count Rumford subsequently measured the quantity of heat by the increase of 

 temperature in a given quantity of water. The quantity of heat which will melt 1 Ib. 

 of ice at Cent, being just sufficient, according to Laplace, to raise the temperature 

 of a pound of water to 75 Cent, or, according to the experiments of Regnault to 79 

 Cent. Clement and Desormes have also shown, that an equal weight of aqueous 

 vapour, whatever may be its temperature and tension, is always produced by one and 

 the same amount of heat. 



As far as we can within the limits of the present work, we shall endeavour to present 

 a full practical view of the subject, giving each class of fuels under their several heads. 



1. Wood, which is divided into hard and soft. To the former belong the oak, the 

 beech, the alder, the birch, and the elm ; to the latter, the fir, the pine of different 

 sorts, the larch, the linden, the willow, and the poplar. 



Under like dryness and weight, different woods are found to afford very different 

 degrees of heat and combustion. Moisture diminishes the heating power in three 

 ways : by diminishing the relative weight of the ligneous matter, by wasting heat in 

 its evaporation, and by causing slow and imperfect combustion. If a piece of wood 

 contain, for example, 25 per cent, of water, then it contains only 75 per cent, of fuel, 

 and the evaporation of that water will require ~gth part of the weight of the wood. 

 Hence the damp wood is of less value in combustion by ^ or f than the dry. The 

 quantity of moisture in newly-felled wood amounts to from 20 to 50 per cent. ; birch 

 contains 30, oak 35, beech and pine 39, alder, 41, fir 45. According to their different 

 natures, woods which have been felled and cleft for 12 months contain still from 20 to 

 25 per cent, of water. There is never less than 10 per cent, present, even when it 

 has been kept long in a dry place, and though it be dried in a strong heat, it will after- 

 wards absorb 10 or 12 per cent, of water. If it be too strongly kiln-dried, its heating 

 powers are impaired by the commencement of carbonisation, as if some of its hydrogen 

 were destroyed. 



The following Table, compiled from the researches of Count Rumford, will place 

 these points clearly before us : 



From every combustible the heat is diffused either by radiation or by direct com- 

 munication to bodies in contact with the flame. In a ^wood fire the quantity of 

 radiating heat is, to that diffused by the air, as 1 to 3 ; or it is one-fourth of the whole 

 heating power. 



II. Charcoal. The different charcoals afford, under equal weights, equal quantities 

 of heat. Wo may reckon, upon an average, that a pound of dry charcoal is capable of 



