CHEMICAL THEORY. 173 



«xi«4cn, and a metal. Products of combustion afe all combi- Disjertation o-n 

 nations of the bases of oxigen gas, and an inflammable sub- J^,^^^ of*^Heat 

 stance. lience, as they arc bereft of that light and heat li^ht, and oom- 

 which they possessed beibre combustion, it is necessary to ''^"" 

 afford lijjit and heat to them to obtain a decomposition, and 

 fl)is decomposition is effectually obtained by offering electric 

 matter to them, as it is that form of light and heat with. 

 which they can combine. One example of this decomposition 

 hris been mcnticmed in a former part of this paper, in which 

 it was shown that water is convertible into its primitive gases ; 

 we shall take anoflier instance of a different substance, namelv, 

 sulphuric acid, which is a product of combustion, and pos- 

 sesses most active properties. On introducing the wires of tlie 

 galvanic pile into a vessel containing this acid, it is soon de- 

 composed, as is the case with water, oxigen gas a|>|iearing at 

 one extremity and intlammable sulphur at the other, and at 

 the same time we observe little or no changes of temperature, 

 as is the case with water, for it absorbs both principles of the 

 electricity. 



The third set of substances on which the influence of gal- 

 vanism has been tried, are inflammables; these are all com- 

 pounds of heat and a base, but they differ in this, that their 

 principles vary very much in the degree of cohesion which 

 exists between them, some are separated by a li-ttle increase of 

 temperature, others scarcely at all by the highest tempera- 

 ture which we can apply ; but to produce this decomposition it 

 is always necessary that a substance should be in contact with 

 them, which contains the matter of light as a component part ; 

 and this, in most cases, is oxigen gas. As an instance of the 

 influence of galvanism on this :^et of substances, we may men- 

 tion charcoal, which is soon ignited, by which it parts with 

 the heat which it contained, and absorbs a principle from the 

 air called oxigen, which at the same time gives out light, 

 which usi^ally exists in composition with it, in its aerial form. 

 To mention another instance, we may take a subject more 

 difficultly inflamed, viz. iron ; this, on being presented to the 

 influence, if it be in any considerable quantity, is only ren- 

 dered red hot, but by being in the form of small wire it burns 

 with very brilliant sparks and great heat ; the product which 

 is obtained from it is an axide of iron. 



The 



