FUEL. 



115 



we can prevent this entirely by using 

 very small wicks, and increasing the 

 number, if necessary, to produce the heat 

 required. Or we may employ one of 

 those lamps, in which a stream of air is 

 allowed to rise through the middle of the 

 flame, or to pass over its surface with 

 such velocity as to produce a more com- 

 plete inflammation than ordinary. But 

 we shall be as much embarrassed in an- 

 other way ; for the oils commonly used, 

 being capable of assuming a heatgreath^ ' 

 above that of boiling water, scorch and i 

 burn the wick, and change its texture, so 

 that it does not imbibe the oil so fast as 

 before. Some have attempted a remedy, 

 by making the wick of incombustible 

 materials, as asbestos, or wire; but still, 

 as the oil does not totally evaporate, but 

 leaves a small quantity of gross, fixed, 

 carbonaceous matter, this, constantly ac- 

 cumulating, clogs the wick to such a 

 degree, that the oil cannot ascend, the 

 flames become weaker, and, in some cases, 

 are entirely extinguished. 



There is, however, a diff'erence among 

 the different oils in this respect, some be- 

 ing more totally volatile than others. 

 But the best are troublesome in this way, 

 and the only remedy is, to change the 

 wicks often, though we can hardly do 

 this and be sure of keeping always an 

 equal flame. 



The second kind of fuel mentioned, 

 peat, is so spongy, that, compared with 

 the more solid fuels, it is unfit to be em- 

 ployed for producing very strong heats. 

 It is too bulky for this; we cannot put in- 

 to a furnace, at a time, a quantity that 

 corresponds with the quick consumption 

 that must necessarily go on when the 

 heat is violent. There is, no doubt, a 

 great difference in this respect among the 

 different kinds of this fuel; but this is the 

 general character of it. However, when 

 we desire to produce and keep up, by 

 means of cheap fuel, an extremely mild, 

 gentle heat, we can hardly use any thing 

 better than peat. But it is best to have 

 it charred, or burnt to a black coal. The 

 advantages gained by having it charred 

 are considerable. When it is prepared 

 for use in that manner, it is capable of 

 being made to burn more slowly and 

 gently, or will bear, without being extin- 



guished altogether, a greater diminution 

 of the quantity of air with which it is 

 supplied, than any other of the solid 

 fuels. 



The next fuel in order is the charcoal 

 of wood. This is prepared by piling up 

 billets of wood into a pyramidal heap, 

 with- several spiracles, or flues, formed 

 through the pile. Chips and brush-wood 

 are put into those below, and the whole 

 is so constructed as to kindle throughout 

 in a very short time. It would burst out 

 into a blaze, and be quickly consumed to 

 ashes, were it not covered all over with 

 earth or clay, beaten close, leaving open- 

 ings at all the spiracles. These are care- 

 fully watched; and whenever the white, 

 watery smoke is observed to be succeed- 

 ed by thin, blue and transparent smoke, 

 the hole is immediately stopped, this be- 

 ing the indication of all the watery vapor 

 being gone, and the burning of the true 

 coaly matter commencing. Thus is a pret- 

 ty strong heat raised through the whole 

 mass, and all the volatile matters are dis- 

 sipated by it,and nothing now remains but 

 the charcoal. The holes being all stopped 

 in succession, as this change of the smoke is 

 observed, the fire goes out for want of 

 aii\ The pile is now allowed to cool. 

 This requires many days; for, charcoal 

 being a very bad conductor of heat, the 

 pile long remains red hot in the cent)-e, 

 and, if opened in this state, would in- 

 stantly burn with fury. 



Small quantities may be procured at 

 any time, by burning wood in close ves- 

 sels. Little pieces may be very finely 

 prepared, at any time, by plunging the 

 wood into lead red hot. This kind of 

 fuel is much used by chemists, and has 

 many good properties. It kindles quick- 

 ly, emits few watery or other vapors, 

 while burning, and, when consumed, 

 leaves few ashes, and those very light. 

 They are, therefore, easily blown away, 

 so that the fire continues open, or per- 

 vious to the current of air which must 

 pass through it to keep it burning. This 

 sort of fuel, too, is capable of producing 

 as intense a heat as can be obtained by 

 any; but in violent heats it is quickly 

 consumed, and needs to be frequently 

 supplied. 



Fossil coals charred, called cinders, or 



