Oifirvatkiit and I/ifcn-via'S rffpi&big Coniliijlion, '^Jt 



{pheres of chemical attraclion for one another: and in various inftances common experience 

 verifies this hypothefis. 



If light be confidered as a diiTerent fpecies of fubllance from caloric, then the theory of 

 Its agency, lately publiflied by Dr. Parr, M. D. may be applied very happily to explain tlie 

 explofion from the combuftijn of oxygen with liydrogen gaz. From a very large indu<5lion 

 of fatls, Dr. Parr infers that, although liehfand caloric fubfill together very commonly in 

 the fame compound fubllance, they fimultaueoufly repel each other on the decompofition 

 of the fubftances with which they were united; and from this repulfion, and alfo the re- 

 pulfion of oxygen and light of one another, he chiefly accounts for the combuftioii of oxy- 

 gen gaz. 



On my principles above dated, we can explain why quickfilver of the temperature of 

 1000% or more, of Fahrenheit's fcale, cannot unite to the oxygen of oxygen gaz ; but 

 ■why at this temperature caloric f^parates oxygen in the gaz (late from oxide of quicklllver : 

 and why at the temperature of between 600 and iooo° quickfilver does unite to the oxy- 

 gen of oxygen gaz ; but at which temperature oxygen gaz is not feparable from the oxide 

 of this metal : and again, why at below 600° oxygen of oxygen gaz can neither unite to 

 quickfilver, nor be feparated from its oxide. 



Thefe principles may be applied varioufly to the interpretation of the phenomena of corn- 

 bullion, and other cafes of chemical combination, according to the ftate of aggregation of 

 the fubftances which have a chemical attrailion for one another. For example ; the oxygen 

 of oxygen gaz cannot unite to the conftituent fubftances of a wax or tallow candle, in a 

 low temv'-rrature ; becaufe the cohefive attra£lion of the wax or tallow, as well as the che- 

 mical attradion between their conftituent fubftances — hydrogen and carbon — counterafl the 

 chemical attradlion between the oxygen of oxygen gaz, and the ultimate particles of hydro- 

 gen and carbon of the candle. But at a pretty elevated temperature, when the wax and 

 tallow are in the vapour ftate, the cohefive attradion no longer fubfifting among the ulti- 

 mate particles of thefe fubftances, and the motion excited by the ignited portion of wax or 

 tallow bringing the ultimate particles of thefe fubftances within the fphere of chemical at- 

 traftion of the particles of oxygen gaz, thefe latter unite firft to the carbon, by virtue of the 

 ftronger attradion between the oxygen and carbon, than that between the oxygen and hy- 

 drogen ; but, in the inftant of this difengagement of the carbon from the hydrogen, a por- 

 tion of this hydrogen unites alfo to oxygen, and thus not only carbonic acid gaz but 

 water is produced : hence the blue jlame, as appears on other cccafions, in which there 

 is combuftion of hydro-carbonate gaz. The remainder of the hydrogen of the 

 decompounded wax or tallow, afcending in the gaz ftate, it unites to the oxygen of 

 oxygen gaz ; and, as in other cafes of combufiion of oxygen gaz with hydrogen, a ivhltL' or 

 Jlraw coloured Jliime is produced. The wick anfwcrs the purpofe, by means of capillary at- 

 traftlon, of applying the wax and tallow in fuch quantities as can be decompounded and 

 combine with the oxygen of atmofpherical air ; hence the combuftion is gradual and equal. 

 The wick itfclf contains hydrogen and carbon; hence, in combining with oxygen of oxygen 

 gaz, it alfo produces a blue flame. Hydro-carbonate gaz being fpecifically heavier than hy- 

 drogen gaz, is another reafon for the blue flame appearing diftinil from the white, and at 

 the inferior part q( the fniflum of a cone of llamc from a burning candle. It is fcarccly 

 ntccfl'jry to fay that hydrogen and carbon arc conftituent fubftances of wax and tallow ; 



and 



