On the Production of Vapor, 73 



mometrical heat. But the parts that are nearer will be 

 obstinately retained, and will not quit it ; they have be- 

 come chymically united with it ; the heat will not be 

 perceptible, and is called latent heat. Hence arises an 

 easy solution of the difficulty some have started against 

 the doctrine, that vapor is a solution of water by fire. 

 They say, if it be allowed that fire rarefies water to such 

 a degree as to render it specifically lighter than air, upon 

 its ascending, the fire will abandon the water, to restore 

 an equilibrium to the cooler air ; and the water will re- 

 turn to its former gravity, and be precipitated ; there- 

 fore, say they, water cannot be made to ascend in vapor 

 upon this principle. But it must be considered, that a 

 greater degree of affinity exists between water and calo- 

 ric, than there does between air and caloric. Hence, 

 though a part of the caloric may quit the pai'ticle of va- 

 por to restore an equilibrium to the cooler air ; yet a large 

 portion of it being chymically united to the water, and, 

 in respect to the air, becoming latent heat, a s.ifficient 

 quantity will be retained to render it specifically lighter 

 than air ; therefore the particle of vapor will ascend. 



A curious phenomenon attending the generation of va- 

 por, is the production of cold. Whenever heat is in- 

 creased and accumulated in one place, it is diminished^ 

 and withdrawn from the parts adjacent. Water, in pas- 

 sing from a solid or icy, to a liquid state, and from a li- 

 quid state to vapor, attracts the caloric from the contig- 

 uous substances. In combustion, the matter of heat is 

 either extricated from its fixed state in the combustible 

 substance, or, as it sometimes happens, it is attracted from 

 the adjacent parts, which are consequently made cooler 

 by the process. This principle has been applied to many 

 useful and economical purposes. The Hungarians, when 

 they travel through the hot deserts, dig a pit about two 

 feet in depth, and bury their bottles of wine in it, cover- 

 ing them over again very close : then they burn straw or 

 reeds over the place, and when the fire is out, they dig 

 up their wine as cool as if it had been put into the cool- 

 est water. This fact is related in the Philos. Trans, of 

 the Royal Society, No. 452. The inhabitants of China, 

 India, Persia and Egvpt^ cool their liquors, used for drink^ 



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