i'Q explain the Vhts'nomena vf Oomlajlion, 50J' 



for the bafe of the combuftible body than for caloric, is 

 thereby attraded, and that the beat ccmibined with it is con- 

 fequently fet at bberty, and ditlufes itfelf among the adjacent 

 bodies. 



To the fecon^ ixjfition of Dr. Thomfon, that the light 

 invariably proceeds from the combuftible body, ancV not from 

 the oxygen gas, there are nuicli Wronger objc6Vions, an<l fiich 

 as, with our prefent colledion of chemical fails, are, I ap- 

 prehend, not readily to be explained. 



It is a part of the theory of the doftor, that oxygen gas 

 poflelTes no light: indeed this is fo material a part, that, iinlcfs 

 it can be lubllantiated, the theory is inadequate to elucidate 

 the phajnoraena intended by it. 



iiow lliall we, however, reconcile the following fa(5ts on 

 the above fujipofitioii ? If nitric acid be expofed to the lifht, 

 it changes colour; it firft grows yellow, afterwards green, "and 

 laftly red, and oxygen gas is difengaged; and on examining 

 the acid we find that it is converted from nitric into nitrous 

 acid. 



It is evident that, as this decompofition is of a chemical 

 nature, the light that occafions it either combines with the 

 oxygen to form oxygen gas, or with the acid to form nitrous 

 xicid: that the latter is nol the cale we are juftified'in fup- 

 pyfing, becaufe we find no difference between acid fo pro- 

 cured and that gained by any other means, and we are ncci'f- 

 filated to conclude that the light has combined with the 

 oxygen, and that the latter is by this mean converted into 

 oxygen gas. The fame reafoning may be applied to the 

 converflou of oxygenated muriatic acid' by light into fimple 

 ,nuiriatic acid. IJnleis ihefe fads can be otherwife fatisfac- 

 torily accounted for, the pofuion of Lavoifier fidl remains 

 with all its force, that light is a conftituent part of oxygen 

 gas. That light forms a neceflary part in the conflifulion of 

 many bodies, is a fa6t too well authenticated to be refuted. 

 The experiments of the Dutch chemiils, who heated toffethcr 

 the filings of tlifll-reut metals with futphur under mercury ; 

 the phanomena of the pyrophori ; the inflammation that 

 takes place from the action of many (jfthe acids on tht oils; 

 and the recent experiments of Dr. ilulme, illuftratc this fa«5l 

 bevond the polhbility of contra Jidion. 



Afterabxly has undergone combuftion, we learn froni 

 this theory that it is deprived of light, and that it is only by 

 means ofra combuftible body that light can he auain trans- 

 ferred to the produil-l of combuliion. Thus water is confi- 

 .il.Tcd by Dr. 'I'lionifon "ns a produd: of coniburLi(n, and 

 confetpitn'Jy depriud of' light. If, fayi he, v.e decoiupoi'e 



thi. 



