SCIENCE OP COMMON THINGS. 197 



What is evaporation ? Danger of wearing wet clothes. 



In the one case, the substance vaporized, being of no 

 use, is allowed to escape or become dissipated in the 

 atmosphere ; while in the other, being the valuable 

 part, it is caught and condensed into the liquid form. 



13O1 What is the vapor from damp linen ? 



The vapor from damp linen, if caught, would be dis- 

 tilled water. 



13OS What is evaporation 1 



The conversion of a fluid into vapor. 



"When vaporization takes place only from the surface of a body, either 

 because the heat has access to that part, or because the evolution of 

 vapor takes place through the medium of a gas or air already present, the 

 action can only be recognised by the diminution of the bulk of the body : 

 this phenomenon is called evaporation. 



1303 What effects are produced by evaporation f 



The substance vaporized absorbs heat from the body 

 whence it issues ; and the body, deprived of a portion 

 of its substance by evaporation, loses heat. 



1304 If you wet your finger in your mouth, and hold it up in the air, 

 why does it feel cold ? 



Because the saliva quickly evaporates, and (as it 

 evaporates) absorbs heat from the finger, making it feel 

 cold. 



1305 If you lathe your temples ivith ether, cologne water, spirits, etc., 

 why does it allay inflammation and feverish heat? 



Because these liquids very rapidly evaporate, and (as 

 they evaporate) absorb heat from the burning head, 

 producing a sensation of cold. 



1306 Why do we feel cold when we have wet feet or clothes f 



Because the wet of our shoes or clothes rapidly eva- 

 porates, and (as it evaporates) absorbs -heat from our 

 body, which makes us feel cold. 



ISO? Why do wet feet or clothes give us " cold?" 



Because the evaporation absorbs heat so abundantly 

 from the surface of our body, that its temperature is 

 lowered below its natural standard ; in consequence of 

 which health is injured. 



13O8 Why is it dangerous to skep in a damp bed? 



Because the heat is continually absorbed from the 

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