FUEL. 



The cotton, or other materials, of which 

 the wick is composed, is not scorched or 

 consumed in the least, because the spirit 

 with which it is constantly soaked is in- 

 capable of becoming hotter than 174 

 Fahrenheit, which is considerably below 

 the heat of boiling 1 water. It is only the 

 vapour that arises from it which is hotter, 

 and this too only in its outer parts, that 

 are most remote from the wick, and 

 where only the combustion is going on, 

 in consequence of communication and 

 contact with, the air. At the same time, 

 as the alcohol is totally volatile, it does 

 not leave any fixed matter, which, by be- 

 ing accumulated on the wick, might ren- 

 der it foul and fill up its pores. The wick, 

 therefore, continues to imbibe the spirit 

 as freely, after some time, as it did at 

 the first. These are the qualities of al- 

 cohol as a fuel. But these qualities be- 

 long only to a spirit that is very pure. 

 If, on the contrary, it be weak, and con- 

 tain water, the water, being less volatile, 

 does not evaporate so fast from the wick 

 as the more spirituous part ; and the wick 

 becomes, after some time, so much soak- 

 ed with water, that it does not imbibe the 

 spirit properly. The flame becomes much 

 weaker, or is altogether extinguished. 

 When alcohol is used as a fuel, therefore, 

 it ought to be made as strong, or free 

 from water, as possible. 



Oil, although fluid like spirit of wine, 

 and capable of burning in a similar man- 

 ner, is not so convenient in many re- 

 spects. It is disposed to emit soot ; and 

 this applying itself to the bottom of the 

 vessel exposed to it, and increasing in 

 thickness, forms, by degrees, a foft and 

 spongy medium, through which heat is 

 not so freely and quickly transmitted. 

 This was observed by Muschenbroeck,in 

 his experiments upon the expansions of 

 metalline rods heated by lamps. It is 

 true 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 ano- 

 ther way, for the oils commonly used, 

 being capable of assuming a heat greatly 

 above that of boiling water, scorch and 

 burn the wick, and change its texture, 

 so that it does not imbibe the oil so fast 

 as before. Some have attempted a re- 

 medy, by making the wick of incom- 



bustible materials, as asbestos, or wire ; 

 but still, as the oil does not totally eva- 

 porate, but leaves a small quantity of 

 gross fixed carbonaceous matter, this, 

 constantly accumulating, clogs the wick 

 to such a degree, that the oil cannot as- 

 cend, the flames become weaker, and, in 

 some cases, are entirely extinguished. 

 There is, however, a difference among 

 the different oils in this respect ; some 

 being 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 a 

 equal flame. 



The second kind of fuel mentioned, 

 peat, is so spongy, that, compared witk 

 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 

 into 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 

 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 previously charred, that is 

 scorched, or burnt to black coal. The 

 advantages gained by charring have been 

 already explained. When prepared for 

 use in that manner, it is capable of be- 

 ing made to burn more slowly and gent- 

 ly, or will bear, without being extinguish- 

 ed altogether, a greater diminution of 

 the quantity of air with which it is sup- 

 plied, than any other of the solid fuels. 

 Dr. Boerhaave found it extremely conve- 

 nient and manageable in his Furnus Stu- 

 diosorum. 



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 brushwood 

 are put into those below, and the \vhole 

 is so constructed, that, when kindled, it 

 kindles almost over the whole pile 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 



