102 



Expansion of 

 "iron on soliJi- 

 licatioa. 



Repulsion 

 between the 

 particles of 

 caloric an 

 unnecessary 

 assumption. 



N(< repulsion 

 between oil 

 and water. 



Sin^ulir 

 phenu.nenon. 



ON THE EFFECTS OF HEAT. 



tion to tbl?, It may be observed, tfcat i«c alwajs contains a 

 quantity of air. Dr. Priestley ascertained, that, when water, 

 previously freed from air, was frozen iu close vessels ; it 

 gave out, on thawing, a quantity of azote; and this he 

 repeated several times, on the same water, and with the 

 same effect*. The expansion of iron during solidification 

 depends probably upon the detention of a quantity of caloric 

 between the pores of the metal in an unconibined state, 

 (i. e. not forming part of the atraosplseres,) and by ham- 

 mering, this may be disengaged. Those bodies, which 

 congeal into a shapeless mass, without any appearance of 

 crystallization, contract, as might be expected, during 

 solidification ; audthis may tend to confirm the explaria- 

 tion given above. 



I have purposely avoided making any mention of the 

 repulsion, supposed to exist, between the particles of 

 caloric ; as I believe, that all the phenomena may be ex- 

 plained according to the ordinary laws of affinity, I will 

 endeavour to explain this, iu one instance ; the expansion of 

 gasses by a diminution of pressure. During the expansion, 

 cold is produced, as was explained before ; the caloric, 

 which rushes in, arranges itself around the particles of the 

 gas, according to its affinity for them ; and thus removes 

 them to a greater distance from each other. In addition to 

 this, it must be recollected, that the particles will exert an 

 attraction, beyond their own atmospheres, upon those of 

 the neighbouring particles ; this will tend to rarefy th« 

 atmosphere^, and of course to expand the gasseS. It is not 

 necessary to suppose, that the particles of water aujd oil 

 repel each other ; if the attraction of the horaogeneal par- 

 ticles be stronger than that of the heterogeneal, they will 

 not unite. 



1 will now mention a phenomenon, wliich I once observed, 

 and which, I think, may be explained according to this 

 theory. During the evaporationofasolution of subcarbonate 

 of soda, which had been exposed to a stream of sulphurcus 

 acid gas ; 1 observed a number of globules to arise, and rua 



* 'Hiis tends to confirm Girtannerls Theory, that azote is an oxide of 

 hirtrogeii— [See also the hypothesis of Berzelius, Joqrnal, vol, XXX, 

 p. 270. C.j ■ 



about 



