Chap. 5.] [ 123 ] 



CHAP. V. 



OF BOILING, VAPOUR, &c. 



EJaftif Fluids diftinguijhed from common Fluids, Specific Gravity of 

 Vapour. In <what Manner Dr. Black ivas led to form bis Tbcorj 

 of latent Heat. Imnenfe Force of Vapour. Bailing. ~ All Fluids 

 boil in a lefs Temperature in Vacua, than under the PreJJiire of the 

 Atjnofpbere. Experiments. Phenomena of Boiling and Evaporation 

 explained. -~lVby Water extinguishes Flame. Spontaneous JL*vapora~ 

 tion. Phenomena of De^vs, Mifts, tyc, 



IF the matter of fire is accumulated to a certain de- 

 gree, the fubftance which is expofed to its aftion 

 will be converted from the ftate of a common fluid to 

 that of an elaflic or compreflible fluid, generally tranf- 

 parent, and extremely rare and light. 



Vapour or ftcam, which is water converted into an 

 elaftic fluid, is of a fpecific gravity one thoufand eight 

 hundred times lighter than water; that is, a given 

 portion of water will, in an elaftic form, occupy one 

 thoufand eight hundred times the fpace it did before. 

 The procefs of paffing from the ftate of a common 

 fluid to that of vapour, is called boiling -, and the de r 

 gree of heat at which a fluid begins to boil is called 

 the boiling point, which, in water, is fixed on Fahren- 

 heit's fcale at 212. 



When a fluid arrives at the boiling point, and pafies 

 from its ordinary ftate to that of vapour, the fame ef- 

 fect takes place as in the converfion of folid bodies 

 into fluids, a quantity of diloric or elementary fire is 

 abforbed without any increafe of temperature ; and 

 when an elaftic fluid is eondenfed, the fame ftre is con r 



Jlantly 



