74? Chemistry. [Lecture 26. 



diately become latent in the liquid, and hence it 

 is not discoverable by a thermometer. By pro- 

 ducing a sudden liquefaction of ice, the cold is 

 so great that all the neighbouring bodies must 

 supply or communicate from their obvious heat 

 the caloric that is to become latent in this lique- 

 faction, and to restore the equilibrium ; and thus 

 it proves in this experiment. If I pour a quan- 

 tity of nitric acid upon ice, it immediately lique- 

 fies, and produces a great increase of cold. This 

 is no other than the obvious heat turned into the 

 latent, to supply the newly produced fluid. This 

 experiment is just the contrary of that where 

 you have water cooled some degress below the 

 freezing point, and if it is at rest it does not 

 freeze ; but if you shake the glass you make a 

 portion of it freeze ; this, on becoming solid, 

 parts with its latent caloric, which becomes ob- 

 vious, and by its means the water which has not 

 frozen has its temperature raised. 



The fourth general effect of heat is the forma- 

 tion of VAPOUR. By vapour I mean a trans- 

 parent fluid, which, like air, is compressible 

 and very elastic, and which suffers great alter- 

 ation in its bulk from considerable acces- 

 sions of heat. If a drop of water is placed on 

 the bottom of an exhausted receiver, it will 

 suddenly disappear, and be converted into a 

 subtile vapour which will fill the vessel : and its 

 pressure against the internal surface will be so 

 strong when heated to a certain degree, that it 



