CHEMICAL THEGRY, ]/! 



f-tnnces varied. I am induced to think that the change con- :6i^orfation on 



sists principally in this, that nitric acid contains a la-gei" por- *''f nature and 

 ,. . , '^ ^ efiecis cf heat, 



tion of condensed hght than atmospheric air, wliich may be light, and corn- 

 supported from an old and * celebrated ex[;eiiraent, which has bustion. 

 been often repeated, and with the same result.- A quantity 

 of atmospheric air was inclosed in, a proper vessel, and fre- 

 quent electric sparks were passed through it, till at length 

 its bulk diminished, and it had lost its properties, having 

 manifestly become nitric acid. Bat the most remarkable 

 part of the experiment is the appearance of th« electric mat- 

 ter, which acts upon it : as I stated before, electricity is a 

 compound of heat and light ; but there are certain substances 

 which can only unite with one of these, which is the case 

 with the experiment now spoken of; the light is absoiLed 

 by the mixture, and the heat evolved, for no sparks are per- 

 ceived, but a considerable quantity ot heat is evolved in a sen- 

 sible form. Many may suppose that this heat escapes from 

 the condensation which occurs, and that the capacity of the 

 substances are changed. One of these opinions appears as 

 likely as the other ; and I think mine is the more preferable, 

 for the condensation of gases does not necessarilj evolve 

 heat, as we observe on presenting gaseous muriatic acid and 

 ammonia to each other. 



As azote is called a simple elementary substance Avhich 

 is uninflammable, so v.e have another which has the 

 same title and property of incombustibility, videlicet, tlie 

 muriatic acid ; and this, like atmo.spheiic air, appears lo 

 be capable of uniting svith the matter of light, and thereby 

 .becoming a supporter of combustion, The real combina- 

 tion of this acid has not been stated, though I have no 

 doubt that the experiments which have been made, in Italyf 

 have great weight in leading us to believe that it is a cuqiibi- 

 nation of oxigen and hydrogen, and may be supposed a pro- 

 duct of combustion. Besides the supporters of conabustion 

 w6 have already mentioned, there appear to be others 

 which deserve that name, which are certain metallic oxides, 

 especially the black oxide of manganese, and the red oxide 

 of lead, 



* Cavendish. t racchiaui. 



Z 2 Before 



