NATUKE OF FLAME.] 



CXDULATORY FORCES. LIGHT. 



89 



the rapid chemical union of cxygen with a combustible. 

 Had Lavoisier been content to say that the phenomena 

 ' were usually dependent on such a combination, it is 

 ; probable that his theory would have existed in a modified ! 

 i form until the present time ; but, in his attempts to 

 make it too general in its application, he effected its 

 ruin ; for, in the course of a few years, the investigations 

 of Sir Humphry Davy into the properties and elementary ! 



ire of chlorine gas, demonstrated the fact, that com- 

 bustion might be effected without the aid of oxygen 

 at all. This was proved by the action of chlorine on 

 i antimony or copper ; and, from that time, the phlogistic 

 nes were put aside ; and chemists have ever since 

 regarded the phenomena in question, not as the result , 

 ny particular kind of combination, but merely as ; 

 j the energetic display of ordinary chemical action. And l 



here we may remark, that there is not, perhaps, in the 

 i whole range of chemical science, a subject that offers so 

 many interesting facts for contemplation, as that to 

 which we have just alluded; for it teaches us that the 

 .ress of human knowledge is often dependent, not so 

 '.i on the discovery of great and important truths, as 

 on the manner in which they are contemplated ; and if 

 men's minds are not prepared for the reception of those 

 trutlis, they will either be disregarded, or else made the 

 .is of propagating error. This was the case with the 

 y of Becher and Stahl, which had the effect of dis- 

 i> every fact that came under its influence. In this 

 for years, it delayed the progress of science, and 

 ed the development of truth. History tells us, that 

 for more than a century before the discoveries of Lavoi- 

 he main facts of his investigations were broadly set 

 forth in the writings of Hooke and Mayew ; but from 

 the circumstance that those facts were premature that 

 s minds were not prepared to receive them, and 

 that chemists were infatuated and led astray by the false 

 doctrines of Becher and Stahl the more humble but 

 important truths of Hooke and Mayew were allowed to 

 pass unnoticed ; and they lay dormant for more than a 

 hundred yean. 



which Combustion may go on. An exami- 

 ii of this question will show that most substances 

 the power of burning in three ways; namely, by 

 slow oxydation, when little or no light is evolved ; by a 

 ibination, when tin- hunting becomes SO 



t<> render itself luminous; and by a still more 

 energetic action when it bursts into (lame. We have 

 examples of the first of these processes in the pheno- 

 mena termed Eremacaunt, or slow burning, aa is wit- 

 nessed in the glowing of phosphorus, and in the lumi- 

 nosity of decaying wood or putrefying fish. In most of 

 these cases, the heat and light evolved at any given 



ient are nut very considerable ; and few persons 

 would be disposed to regard the phenomena as those of 



u-tioM ; but wiii-n it becomes known that the total 

 amount of heat, and ]wrhaps also of light, generated 

 during this slow kind of oxydation, is exactly the same 

 as that evolved during the most rapid combustion of the 

 same substances, there will be no difficulty in under- 

 standing that the i>lirnom<-na in the two cases are 



able to the same kind of chemical action, and be- 



i the same category. 



-.(dud mode, of combustion is observed when 

 _'a, or the vapour of ether, alcohol, or wood-spirit, 

 with air, and brought under the influence of 

 'fjy platinum or fine plain, urn wire. This is best 

 if the wire in the flame of 



either of the combustibles, then blowing the flame out, 

 ami allowing the va|x>ur or gas to play on the surface of 

 tin; metal : in this way the platinum will keep up the 

 n, and will continue to glow, although the 

 vapour or gas will not be inflamed. 



The third kind of mmbustion is produced whenever 

 a sutticiently high t- is applied to any kind of 



vaporous matter so a- to inflame it. The temperature 

 at which this is effected varies with different combus- 

 tibles; gome take fire at ordinary teniyu-ratures, as 

 .y-dividrd phosphorus, and pliosplmretted hydrogen ; 

 whereas, solid or massive u.s require* a tempe- 



VOL. i. 



rature of 140 to inflame it ; sulphur takes fire at about 

 500 ; hydrogen and carbonic oxide at 1000 (which is a 

 red-heat) : and coal gas, ether, txvrpentine, alcohol, oil, 

 tallow, and wood, at about 2000 (or an incipient white- 

 heat); but when once inflamed, they all continue to 

 burn at a very exalted temperature. 



The Nature of Flame. The preceding remarks will be 

 sufficient to show that flame is nothing more than gase- 

 ous matter burning at a very high temperature. We 

 may prove this by experiment. If we take a coil of 

 iron wire, or a piece of watch-spring, arm it at one end 

 with a fragment of burning wood, and then introduce it 

 into a jar of oxygen gas, the metal will take fire and 

 burn with the most brilliant scintillations, bvit it will not 

 produce flame. Again, if we expose wood to the action 

 of heat in a closed vessel, so as to drive off all volatile 

 matters and obtain its fixed solid constituent, charcoal, 

 we may burn it in an atmosphere of oxygen without pro- 

 ducing flame. In both of these examples, the absence 

 of flame is entirely due to the absence of gaseous matter 

 in the combustibles; and to show that a high tempera- 

 ture is necessary to produce flame, we have only to burn 

 coal gas, alcohol, ether, or wood-spirit, at the low 

 temperature of glowing platinum, and they will not 

 inflame. 



It may be thought, perhaps, that in the case of wood, 

 tallow, oil, phosphorus, <tc. , the flame cannot result from 

 gaseous matter, because those bodies are either solid or 

 liquid in their nature ; but a little consideration will teach 

 us, that, in the act of burning, they all become converted 

 into gases or vapours. This may be easily demonstrated 

 in the case of a common candle or oil-lamp, the wick of 

 which conveys the fluid combustible to the flame, where 

 it is decomposed and converted into vapour. Now, if wo 

 hold a small glass tube, or even a piece of tobacco-] 

 in the flame of the candle, so that the end of the tube 

 shall be exactly over, and almost in contact with, the top 

 of the wick, it will collect the com- i >, >i 



bustible vajKrnr and convey it out of 

 the flame, whence it may be burnt 

 by applying a light to the opposite 

 end of the tube (Fig. 81). This ex- 

 periment also proves that nV 

 hollow : it consists, in fact, of 

 cones placed one over the other. The 

 inner cone, which is of a dark colour, 

 and surrounds the wick, is formed 1 iy 

 the vapour of the decomposed tallow. 

 The second cone is the luminous one ; 

 it envelops the preceding on all s 

 and consists of the ignited particles of the gas making its 

 way outwards to the air. The third, or outermost cone, 

 is nearly invisible; it constitutes that pale blue film 

 which everywhere surrounds the luminous part of the 

 flame. We may make thia cone more evident by bring- 

 ing a piece of thread moistened witlt salt into the lower 

 edge of the flame, when the cone will be instantly lighted 

 up with a deep yellow tinge. Another mode of discover- 

 ing it is to screen off the luminous cone by means of the 

 *"" ' ' or it may be rendered visible by intersecting the 



hand : 



flame with a piece of fine platinum wire, or wire gauze, 

 the ignition of which discovers the exact boundary of 

 the cone. This cone is made up of gas in an actual 

 state of combustion ; for it is here, and here only, that 



'ess of oxydation is rapidly going on. 

 1'inite of Light ill Flame.. A little experience will 

 inform us that different combustible substances burn 

 with different degrees of intensity (Fig. 82). We. will 

 endeavour to show that this is' wholly dependent on the 

 number of solid particles that are ignited within the 

 flame. If we take a jet of hydrogen gas and fire it, or 

 make use of a flame of alcohol from a common spirit 

 lamp, we shall notice that neither of these bodies burn 

 with any great amount of light ; the case is very differ 

 however, with a candle, or even with a jet of coal gas. 

 Now, in the former examples the hydrogen and the 

 spirit do not contain any solid particles, and conse- 

 quently do not contain any species of matter that can, 

 ! by its ignition, evolve light : but in the latter examples 



