408 On the Heat developed in Combustion 



new substance formed should be considerable ; for it is 

 certain that the most intense heat, if it be developed in 

 a very small particle of matter, may exist without pro- 

 ducing any sensible effect which could give us any indi- 

 cations of its existence. 



It is not less true that the chemical union of two 

 atoms, two different elementary substances, ought al- 

 ways, under every circumstance, to be accompanied with 

 one and the same change of temperature ; for this union 

 takes effect in a place so distant, relative to all the 

 other bodies (if, in every case, all the interstices are not 

 filled with particles of an ethereal fluid), that we can- 

 not conceive how the change of temperature in question 

 may be either augmented or diminished by the effect 

 of the action of these surrounding bodies. 



It is extremely probable, from what we have been 

 able to remark in a great number of phenomena, that 

 the approximation of the elementary particles of bodies 

 is always accompanied by an elevation of their tempera- 

 ture ; and as there cannot be new substances formed ex- 

 cept in consequence of an approximation and the chem- 

 ical union of elementary particles, we may conclude 

 that there cannot be new chemical compositions without 

 a development of heat. 



We may form an idea of what passes in combustion, 

 by considering the phenomena which take place when 

 water freezes. 



At a certain temperature, which is invariable, the 

 molecules of the liquid, are disposed to approximate in 

 order to form a solid body, ice ; and the first particle 

 of ice which is formed is accompanied by a develop- 

 ment of a certain quantity of heat, which quantity is 

 invariable. 



