FUEL 491 



ructTSIUB and PUCUSO1. Two substances obtained by Dr. Stenhouse, 

 by acting with sulphuric acid on certain species of Fucm. 



F1TD, or Woollen Waste, is the refuse of the new wool taken out in the scribbling 

 process, and is mixed with the mungo for use. See MUNGO. 



FUEL. (Combustible, Fr. ; Brennstoff, G-er.) Such matters as are used for the 

 economical production of fire. Wood, Turf, Coal, are familiar examples. Fuels 

 differ in their nature, and in their power of giving heat, and consequently in their 

 properties of developing heat when undergoing combustion. It is therefore important 

 to understand the principle upon which depends the value of a particular fuel. 



With the philosophy of the question we are scarcely called upon to deal in the 

 present volume. A few remarks may not, however, be entirely out of place, and they 

 may servo to guide the reader in his consideration of the production of heat by com- 

 bustion which is the only means of production with which we have to deal. 



In his ' Novum Organum ' Bacon writes : ' Heat is an expansive motion whereby 

 a body strives to dilate and stretch itself to a larger sphere or dimension than it had 

 previously occupied. This difference is most observable in flame when the smoke 

 or thick vapour manifestly dilates and expands into flame. . . . Heat is a motion, 

 expansive, restrained, and acting in its strife upon the smaller particles of bodies. 

 But the expansion is thus modified while it expands in all ways, it has at the same 

 time an inclination upwards but the struggle in the particles is modified also, it is 

 not sluggish, but hurried and with violence.' Bacon's Works, Spedding"s Trans- 

 lation, vol. iv. 



Count Rumford's paper read before the Royal Society, January 25, 1798, entitled, 

 ' An Enquiry concerning the Source of the Heat which is excited by Friction,' contains 

 the results of his experiments made at Munich on the boring of brass cannon. He 

 shows that by friction so much ' heat was generated ' that the water in which the 

 cannon during the operation of boring was placed, gained heat so rapidly that ' at 

 two hours and twenty minutes it was 200, and at two hours and thirty minutes it 

 actually boiled.' He finds by careful estimates that the total heat produced was 

 sufficient to raise 26-58 Ibs. of ice-cold water to its boiling point, or through 180 F. ; 

 and that this heat is equal to that given out by the combustion of 2303'8 grains (or 

 4^ oz. troy) of wax. Considering this interesting subject Count Rumford asks, 

 ' What is heat ? Is there any such thing as an igneous fluid ? Is there anything 

 that can with propriety be called caloric ? ' He then continues, ' We have seen that a 

 very considerable quantity of heat may be excited by the friction of two metallic 

 substances, and given off in a constant stream or flux in all directions, without inter- 

 ruption or intermission, and without any signs of diminution or exhaustion. . . . 

 It is hardly necessary to add, that anything which any insulated body or system of 

 bodies can continue to furnish without limitation cannot possibly be a material sub- 

 stance ; and it appears to me to be extremely difficult, if not quite impossible, to form 

 any distinct idea of anything capable of being excited and communicated in those 

 experiments, except it be motion.' 



Locke says, ' Heat is a very brisk agitation of the insensible parts of the object 

 which produces in us that sensation from whence we denominate the object heat ; so 

 what in our sensation is fieat, in the object is nothing but motion' 



Sir H. Davy wrote in 1812: 'The immediate cause of the phenomena of heat, 

 then, is motion, and the laws of its communication are precisely the same as the laws 

 of the communication of motion.' 



These are the views entertained by those who do not believe heat to be matter. 

 The dynamical, or as it is often called, the mechanical theory, of heat, assumes all heat 

 to be a motion of the ultimate particles of matter. 



The material hypothesis of heat, which held possession of the minds of most experi- 

 mental philosophers especially of Lavoisier and of Black embraced the view which 

 is well expressed by Gmelin in his ' Hand-book of Chemistry.' He says : ' Heat is 

 the substance whose entrance into our bodies causes the sensation of warmth, and its 

 egress the sensation of cold.' That is, heat was regarded as an infinitely subtile 

 agent a positive entity which interpenetrated matter, in which it lay hidden, or 

 latent, until it was by some exciting powers disturbed. This differs little, if anything, 

 from the hypothesis of an all-pervading ether, which, being disturbed, produces one 

 or the other of the so-called physical forces. 



Heat can be produced by the effect of gravitation a falling body, for example 

 but for all practical purposes water is really the only body we can employ to produce 

 the motion necessary for the production or development of heat. A cataract or a 

 river may be regarded as a constant means of obtaining the required motion. But 

 this water has been lifted from the sea-level by the action of the solar heat, which 

 has been produced in the sun, by, it would appear, the actual combustion of some 

 material substances. Therefore, the heat which we obtain by the influence of tho 



