flamh:. 127 



brilliant light in combustion. This light is further increased by 

 the fixed and dense nature of the phosphoric acid which is 

 produced. This substance, unlike the gaseous products in the 

 two former instances, is a solid incombustible substance, capable 

 of being ignited to an extremely high point, without decompo- 

 sition. 



Thus we perceive, that as the light is derived from the ignition 

 of solid matter, and as these solid bodies are only held in solution 

 by gases in definite proportions, our chief aim should be, so to 

 conduct the process of combustion as to produce the highest 

 degree of temperature without the actual combustion of the solid 

 matter. 



Although by some it may be deemed superfluous, yet, since 

 much depends on the true meaning of the terms ignition and 

 combustion, it will not be amiss here to point out, the distinction 

 between them. If we take a piece of lime, or a common brick, 

 and heat it to redness, it will be found that its properties will not 

 be altered, for it will resume its former appearance on cooling : 

 this is ignition. If, on the other hand, we submit a piece of 

 wood to the action of fire, we perceive that, immediately on arriv- 

 ing at a certain temperature, its properties suddenly alter; it 

 becomes black ; and heat and light are copiously evolved from 

 it: this is combustion. Great regard should be paid to these 

 two peculiar states of bodies, as the light depends entirely on the 

 ignition, and not the combustion ; because when the combustion 

 is most perfect, and the solid matter entirely consumed, the light 

 is least. For example, if we allow a jet of carburetted hydrogen 

 gas to burn as it issues from the pipe, the light produced is ^ 

 brilliant, but only in that part in which the carbon is ignited 

 without entering into combustion ; for in those parts where the 

 combustion is most perfect, that is to say, in those parts which 

 are immediately in contact with the atmosphere, the light is very 

 feeble. In order to prove this, it is only necessary to insert a 

 piece of metal, so thick as not to be readily heated, in the midst 

 of the bright flame; this will conduct away the heat so rapidly 

 as to defend from its action the carbon, which will consequently 

 become deposited in abundance on the surface of the metal. If 

 the piece of metal be now applied to the apex of the flame no 

 charcoal will be deposited, in consequence of its having entirely^ 

 combined with oxygen, and become converted into carbonic 

 acid. 



