134 Why Water extinguifies Flame. [Book IL 



any considerable agitation of the fluid, or emifllon of 

 fteam. 



3dly, The rcafon why water, either hot or cold, im- 

 mediately extinguimes flame, will eafily be understood 

 from what has been premifed. When a quantity of 

 water is thrown upon an ignited body, it is immedi- 

 ately converted into vapour, and this procefs fuddenly 

 deprives the burning body of as much elementary fire 

 as the vapour is naturally difpofed to abforb. If 

 therefore the water is applied in fufficient quantity, the 

 whole of the caloric will be imbibed by the evaporation, 

 and the body will be left totally deftitute of heat. For 

 the fame reafon it is evident, that water will prevent 

 the melting of metals, or of any fubftances which re- 

 quire a degree of heat fuperior to the boiling point, to 

 render them fluid: for the water, being in contact with 

 the other fubftance, will not permit its temperature to 

 increafe, and all the fuperfluous fire which would heat 

 it above the boiling point, if the water was not there, 

 is carried off by the evaporation of that fluid *. 



* Perhaps it may not be quite unacceptable to the reader to 

 notice in this place the vulgar paradox : " That when water is 

 boiling in a vcflel, the bottom is cool ; but the moment it ceafcs to 

 boil, the bottom becomes hotter." The whole of the paradox 

 appears to be founded on an error of the fenfe. When a perfon 

 applj.es his finger -to the vefiel, though he applies it for a confider- 

 able time, it is not heated more than he can endure, for the blood in 

 the courfe of its circulation lofes fome of its heat before it arrives 

 at the extremities ; and till the blood in the extremities is heated 

 to the fame degree with that of the heart we feel no pain from 

 burning ; but as icon as this is effefted, the leali degree of heat 

 becomes painful. When the finger is firft applied to the bottom 

 of the veffel after it is taken olF the fire, the heat is endured for 

 thefe rcafons. When the boiling ceafes, it is natural to take the 

 fame finger (for having dirtied one, people feldom chufe to take 

 another) ar.d that finder, being already heated alniott as much as 

 it could bear, now finds the heat at the bottoai of the veflel exqui- 

 fitely painful. 



The 



