428 Rev, Mr. Emmett oji Combustion, {Dec. 



gas would be inflammables.* Were it vapour of sulphur, then 

 iron, copper,t and many other metals, would be inflammables, 

 and sulphur the supporter, while zincj and charcoal would be 

 uninflammable. Were aqueous vapour our atmosphere, potas- 

 sium would be, perhaps, almost the only combustible.^ Hence 

 it appears that the terms (I speak of their philosophical applica- 

 tion only) supporter of combustion, and inflammable substance, 

 are merely relative ; that which is a supporter in one case is 

 inflammable in another ; and vice versa. But again, in cases of 

 combustion, why is one body a supporter of combustion rather 

 than the other? When light and heat accompany chemical 

 combination, the phenomenon is properly and truly styled 

 combustion : each of the substances contains a definite portion 

 of caloric ; during combination condensation takes place; there- 

 fore, the sum of the content of the interstices between the parti- 

 cles of the bodies combined is diminished, and consequently 

 heat is excited. If this be accompanied with light, why is the 

 term combustion to be confined to those cases which require the 

 presence of oxygen, chlorine, or iodine ? Is not the action which 

 takes place between filings of copper, or iron and sulphur, as 

 truly combustion ? The action is the same ; the phenomena are' 

 the same. However, if it be desired to place under one general 

 bead those substances which resemble oxygen in their general 

 properties, this is to make a truly scientific arrangement ; but 

 why hmit the term combustion to those cases which require 

 iheir presence, whilst multitudes of examples, answering every 

 o-equirement, can be produced, where they need not be present? 

 There is one class of phenomena which extends through, and 

 €ixiiibits itself in, every part of an extensive scale : whenever 

 bodies enter into chemical union, a change of temperature 

 accompanies the change which takes place in the properties of 

 the substances. Metals become oxides ; sulphur, phosphorus, 

 carbon, and some other bodies, become acids ; potassium, 

 sodium, Sec. alkahes, if oxygen be concerned as the supporter of 

 combustion. In other cases, as the union of carbonic acid gas 

 to hydrate of hme, a neutral salt results ; yet in all cases of this 

 •order, condensation takes place, heat is evolved in various 

 degrees. Now since under the influence of oxygen, combustion 



• If a stream of oxygen be admitted into a vessel of hydrogen gas, and an electric 

 «park be passed just above the orifice, a Cone of flame will immediately appear, and 

 appearances will be the same as when the stream is hydrogen, and the surrounding 

 soedium oxygen. 



f A piece of copper foil inflames spontaneously in vapour of sulphur : if iron or 

 copper filings be n)ixed with sulphur, on applying a moderate heat, violent ignition 

 instantly takes place. 



J Zinc cannot be made to unite directly with sulphur. 



§ This may, perhaps, be controverted, since charcoal and iron, when ignited, decom- 

 pose water ; but in this case, external heat is applied ; nor do I recollect to have seen 

 any experimental proof that aqueous vapour alone can support the combustion of char- 

 ^oal or iron. 



