216 LAVOISIER'S THEORY OF COMBUSTION. 



that the condensation of oxygen was always ne- 

 cessary to combustion. 



It is doubtless true, that during the chemical 

 union of gaseous oxygen with metals, its volume 

 is greatly diminished, and a large amount of 

 heat disengaged, by which the metals are ex- 

 panded into the luminous state when the process 

 is rapid. But it is equally certain, that the com- 

 bustion of wood, coal, naphtha, alcohol, aether, 

 and a thousand other bodies, is attended with 

 expansion instead of contraction of the combining 

 materials, as illustrated in the third chapter, 

 when treating of explosion and deflagration. It 

 is here worthy of special attention, that while 

 Lavoisier pointed out the vast abundance and 

 importance of oxygen in combustion, respiration, 

 acidification, and fermentation, he did not ex- 

 plain the cause of oxidation, which is indispens- 

 able to a theory of combustion. 



The most direct and compendious method of 



remains fixed. Hence also it is, that around the bottom of a 

 candle flame, where the heat is not sufficient to ignite the carbon, 

 there is always a circle of bluish light, which proceeds from the 

 combustion of hydrogen. When potassium is thrown upon 

 water, it enters into a state of vivid combustion ; the water is 

 decomposed, and the metal expanded into red light. At the 

 same time, a portion of the hydrogen thus decomposed, unites 

 with the potassium, producing a beautiful purple and rose co- 

 loured flame; that is, the blue and red colours on combining 

 produce a reddish purple. Query, May not all the diversities 

 in the colours of heterogeneous light resulting from combustion 

 be thus accounted for in a very simple manner ? 



