ELECTRO-CHEMICAL PRINCIPLES. 159 



of combustion of the charcoal is the effect of a condensation, consequently 

 namely, that the oxigen gas has parted with the caloric which cause( j b y con , 

 was employed in maintaining its gaseous form 5 and it is clear, densation, 

 that the fire owes its origin to some other circumstance. Those 

 who may not be disposed to approve the electro-chemical ex- 

 planation, may, observe, that the fire in this combustion is pro- 

 duced by the difference between the specific heats of oxigen 

 gas, and carbonic acid gas. But, although it cannot be denied, nor by change 

 that such a cause (or incident) may contribute to (or accompany) ° ca P acit y* 

 the production of heat, it can be easily shewn, that it is not the 

 principal or general cause j because the nitric acid in which the 

 oxigen still preserves its property of producing fire with a num- 

 ber of combustible bodies, possesses as little specific heat as the 

 carbonic and the sulphuric acids. In like manner, the difference 

 of specific heat between the metallic sulphurets and that of a 

 metallic body, is too inconsiderable to afford a plausible reason 

 for the fire produced by sulphuration. 



When a combination already formed, as, for instance, be- Electro- 

 tween A and B, is decomposed by the more powerful affinity )J e £ l a c t aI f ause 

 of a third body C, so that this last separates A from the combi- simple elective 

 nation AB, and forms CB — such a decomposition is usually a jJ n S' 

 accompanied with an elevation of temperature, or even with 

 fire j and this elevation is greater the more considerable the 

 difference may be between the affinities of A and of C to 

 B. We may form a notion, that this effect is owing to a more 

 perfect neutralization of the electro-chemical properties of the 

 constituent parts in the new, than in the old combination. If, 

 on this occasion, B were oxigen, and A and C two combustible 

 bodies, the electro-chemical nature of B must be admitted as 

 more perfectly neutralized by C than by A j and at the instant 

 when A is reduced to its original combustible state, it receives 

 from C, which loses its like state, a quantity of positive 

 electricity, equal to what it had lost when it entered into combi- 

 nation with B. 



When bodies combine with others, in some instances more The properties 

 positive, and in others more negative, than themselves, are ^rem^rkably 

 found after these two circumstances in very different states ; as affected by 

 sulphur, for instance, is in a quite different state in the sulphuric "J 1 !.- 



acid, from that which it possesses in the sulphuret of lead. From components," 

 the former it can be disengaged by a number of electropositive e.^ sulphur 



bodies, 



