1826.] Mev, Mr, Emmett on Combustion* 4^7 



tutes about four-fifths is almost inert, serving only to moderate 

 the energy of the other, which consists of one-fifth part ; they 

 ascribed to this one-fifth part, which they denominated oxygen, 

 all the properties formerly attributed to the whole atmosphere, 

 which it possesses in a high degree. They followed up the old 

 plan, limiting the cases of combustion to those which cannot 

 take place without the presence of oxygen, which now began to 

 be considered as the only " supporter." On examining the 

 products of combustion, Lavoisier was the first to determine 

 with rigid accuracy, that oxygen becomes united to the inflam- 

 mable body, that the sum of the weights of the oxygen wliich 

 disappears, and of the combustible consumed, is precisely equal 

 to the weight of the product. Hence he inferred that at a cer- 

 tain temperature, any one of the class of inflammables attracts 

 the particles of oxygen so powerfully as to separate it from the 

 caloric with which in its gaseous state it is combined : hence 

 this caloric is liberated. Hence he supposed all the light and 

 heat that are evolved to be separated from the oxygen gas.* 

 The old doctrine which recognized in oxygen the only supporter 

 of combustion, continued to prevail, until chlorine, iodiae, and 

 perhaps fluorine, were added to the fist. Now all these are 

 termed the " supporters of combustion." Are the interests of 

 science promoted by making this distinction between supporters 

 of combustion and inflammables? In the common affairs of life 

 the distinction is useful ; for the atmosphere is the only gaseous 

 matter which comes under universal notice, and popularly it is 

 with reference to it that substances are inflammable or unin- 

 flammable. But extend the distinction to the four " supporters," 

 and we find that carbon is inflammable, oxygen being the sup- 

 porter; but it is uninflammable in chlorine and (if I recollect 

 facts distinctly) in iodine. Boron is in the same state : other 

 examples might be quoted; but since they will be well known 

 to your chemical readers, 1 shall not quote any others, particu- 

 larly since these show that a body is inflammable when exposed 

 to one supporter, but inert when another is applied. Hence 

 each supporter must have its own class of inflammables. 



But I extend the application of the query. Were our atmo- 

 sphere composed of hydrogen gas, then oxygen gas and chlorine 



chemical action, presents itself : therefore it is merely a mixture. Besides, the proper- 

 ties of oxygen gas are in nowise changed ; they are only moderated ; and the azote pro- 

 duces no positive effect, except that of moderating the otherwise too powerful energy of 

 the oxygen. 



* When it is considered that all bodies absorb much caloric during their conversion 

 into the gaseous state, which they evolve again during condensation, it is difficult to see 

 how fhis most eminent philosopher could have made any other supposition; for the 

 science was just beginning to be framed ; he had no means of ascertaining the quantity 

 of caloric remaining in the product of combustion. Hence, reasoning in a truly philo- 

 sophical manner, he concluded that, in the case of phosphorus and iron especially, the 

 Jieat evolved is tliat which is required for the conversion of oxygen into a gaseous state ; 

 and surely he made a right assumption, when the contrary could not be proved. 



