COMBUSTION. 



species. This genus is very imperfectly 

 known, and being a very fine one, de- 

 serves the attention of the cultivators of 

 exotic plants. 



COMBUSTION. The temperature of 

 bodies may be raised by various means, 

 which are generally such as produce an 

 agitation among the particles. The sun's 

 light, and also the chemical or mechani- 

 cal actions of bodies upon each other, if 

 sufficiently intense or rapid, produce 

 this effect. One of the most generally 

 kfiovvn methods of producing a high 

 temperature consists in striking or rub- 

 bing bodies together ; and there is no ac- 

 tion more familiar to us, for this pur- 

 pose, than the striking of a Hint against a 

 piece of steel. Whenever an elevated 

 temperature is thus produced in a body 

 communicating with the open air, it is 

 observable that, according to the nature 

 of the body itself, the heat is either con- 

 ducted away, and nothing farther hap- 

 pens, or else it continues, and even in- 

 creases, so as to spread by communica- 

 tion through every part of the body, and 

 produce a change in it's nature. Thus, if 

 one corner or extremity of a thin piece 

 of stone or glass be made red hot, it will 

 soon become cold again, and no farther 

 effect will follow ; but if the corner of a 

 piece of paper or wood be heated in like 

 manner, it will not, in common circum- 

 stances, become cold again without al- 

 teration, but the heat will be communi- 

 cated to the whole mass, and will con- 

 tinue until the body shall have undergone 

 a remarkable change. This phenomenon 

 is called combustion or burning ; the bo- 

 dies which are liable to it are called com- 

 bustible; and after they have undergone 

 this process they are said to have been 

 burned. 



There are scarcely any chemical 

 changes, by which heat is produced, suffi- 

 cient to exhibit the appearance of light, 

 unless oxygen be in the act of entering- 

 into combination with a combustible body. 

 One of the earliest observations respect- 

 ing ordinary combustion must have been, 

 that it cannot take place without com- 

 mon air, and that it is extinguished by 

 shutting out the air. It is now well 

 known, that the air acts only by means 

 of its oxygen, which unites with and 

 changes the combustible body. 



The earlier doctrines respecting heat 

 and fire are scarcely entitled to notice ; 

 and certainly must not occupy our pages. 

 It will be sufficient, for us to remark, 

 that the hypothesis of an element called 

 fire, which was supposed to escape from 



burning bodies and ascend to a sphere a- 

 bove, was modified by Beccher and Stahl, 

 by the supposition of a general principle, 

 assumed to exist in all combustible bodies, 

 and denominated phlogiston ; capable of 

 passing in combination from one body to 

 another, or of Hying off' with a violent 

 agitation, in which the heat was imagined 

 to consist. As this the'ory was establish- 

 ed upon the observation of a number of 

 striking chemical facts, it was for a long 

 time universally received. Various modi- 

 fications were, however, proposed by 

 different chemists, as discoveries came 

 to be made ; particularly with regard to 

 the agency and combination of air in bo- 

 dies, and afterwards those of the exist- 

 ence of oxygen, and the laws by which 

 heat, or the cause of temperature, is go- 

 verned. These advances led to the re- 

 jection of phlogiston altogether ; a 

 change of theory, which was more rapid- 

 ly effected by the patronage, exertions, 

 and scientific labour of Lavoisier ; who 

 devoted the influence of an elevated situa- 

 tion, the extent of his fortune, and the 

 powers of an uncommonly clear and 

 comprehensive intellect, to this object. 

 It is to be regretted that, with claims 

 so well founded and so great, this philoso- 

 pher should have sought for more ; but it 

 is certainly true, that he himself gave sup- 

 port to the powerful cry of that party, 

 which has proclaimed him the author of 

 the modern theory of combustion ; where- 

 as, if they hud continued to do justice to 

 Rev, Hooke, Mayow, Hales, Bayen, 

 Priestley, and others, there would have 

 been little of absolute facts left for La- 

 voisier to claim in the way of original dis- 

 covery; though it would be difficult to 

 find adequate terms to express the obli- 

 gation under which the scientific world 

 is placed with regard to him, for his am- 

 ple and accurate repetition of experimen- 

 tal investigations, and the very luminous 

 and able manner in which he has digest- 

 ed and stated the whole mass of facts, 

 and applied them to theoretical results. 

 Combustion, as understood by modern 

 chemists, is the rapid combination of oxy- 

 gen with a body, winch is attended with in- 

 crease of temperature and the emission of 

 light. The burned body is therefore an 

 oxygenated compound. Thus we may 

 form a notion of combustion by burning 

 a piece of iron wire. If the diameter of 

 the wire be very small, such, for ex- 

 ample, as half the thickness of a hair, 

 and it be made up into a tuft like wool, 

 it may be lighted by a candle, and will 

 burn, like other more readily comb; 



