ON THE EFFECTS OF HEAT, 99 



io not part with a sufficient quantity of caloric, to equalize 

 the neighbouring atmospheres; the shock therefore must 

 be repeated : Hence it follows, that nitric acid contains a 

 large qnantit)' of caloric : but, as its specific gravity greatly 

 exceeds the mean of that of its component part?, the atmo- 

 sphere, wliich surrounds its particles, must be very dense. 

 It is needless to add, that this is confirmed by almost every 

 experiment, in which nitric acid is employed. 



Again, azotic and hidroeen gas cannot be. combined arti- Production of 

 ficially, because the affinity, which these gasses have for 

 caloric, greatly exceeds that which they have for each other. 

 But when the hidrogen is nascent, its affinity for azote, 

 being assisted by that of the surrounding bodies for caloric, 

 causes their union. It may even be conceived, that the 

 liidrogen seizes on a part of the caloric of the azote ; and 

 the whole quantity being divided between the two, the re- 

 sistance is diminished ; they then unite, and ammonia is 

 produced. 



The effiicts of compression on gasses may be thus ex- Effects of 

 plained. By bringing the particles nearer to each other, compression 

 the density of their atmospheres is increased ; they therefore 

 exert a greater resistance, and the elasticity of the gas is 

 increased also. If the compression be sudden and violent, 

 a quantity of caloric is disengaged. It is exceedingly pro- 

 bable, that, in this case, the elasticity of the gas is injured. 

 I have frequently thought, that I have observed this effect 

 produced on atmospheric air ; and I recollect to have seen 

 the same remark in print, although I cannot precisely re- 

 member the place. If a mixture of oxigen and hidrogen 

 be suddenly compressed, the heat, which is extricated, will 

 equalize the atmospheres, and the gasses will cojubine. If 

 the compression were gradually applied ; it is probable, that . . 



no union would ttike place. It must be evident, that rare- tiou. 

 faction will produce an effi^ct contrary to that produced by 

 compression. A part of the air being removed, the atmo- 

 spheres will meet with less resistance ; they will of course 

 expand. By ihis means there will be occasioned, so to 

 speak, a vacuum of caloric; it will therefore rush in from 

 the neighbouring bodies, and thus cold will be produced; but, 

 on readmitting the air, there will be a redundance of caloric; 

 H 2 the 



