124 Phenomena of E oiling explained. [Book II. 



Handy emitted, and fenfible heat is confequently pro- 

 duced. If we obferve the heating of water, we ihall 

 find that the heat flows into it very fad, till it arrives 

 at the boiling or vaporific point. Suppofe that in the 

 laft five minutes its heat is increafed 10, in the next 

 five we fhould expe<5t that it would at lead be fix or 

 feven more; but this is not in reality the cafe, for 

 though very little of the water is evaporated, yet the 

 remainder is not fenfibly hotter. In order to prove 

 the time neceffary to convert a quanticy of water into 

 vapour, a number of flat-bottomed cylindrical vefiels 

 of iron were conftruded, into which a quantity of wa- 

 ter was put, at the temperature of 54. The water 

 was heated to the boiling point in four minutes, but it 

 was not evaporated in lefs than twenty. Thus it is 

 evident that the water had acquired 158 of heat in 

 the fpace of four minutes ; znd confequently, as the 

 heat of the fire continued the fame, it required five 

 times 158 of heat to convert it into vapour. This irn- 

 menfe acceffion of caloric is, however, neither fenfible 

 in the water nor in the vapour, for if a thermometer 

 is applied to the (team, it will not be found hotter than 

 the boiling water ; it is therefore really abforbed by the 

 fluid, which is converted into vapour, and is retained 

 in the latter in a combined ftatc. When the vapour 

 is condenfed in the refrigeratory of a {till, the latent or 

 combined fire is once more rendered fenfible, for the 

 refrigeratory is heated much higher than the fenfible 

 heat of the vapour, as the heat, if accumulated, would 

 raife the thermometer to more^than 800. 



We are informed by Dr. Crawford, that Dr. Black, 

 vho is certainly the author of the prefent theory of 

 heat and fluidity, f was firft led to the difcovery of the 

 abforption of heat by aqueous vapour, in confequence 

 of an unexpected appearance which occurred in :<:i 



experiment 



