I6O LATENT HEAT OF STEAM. 



the mercury in the bulb of a thermometer. The 

 latent heat of nearly 1000 in steam becomes man- 

 ifest on its condensation into water, by raising the 

 temperature of about sixfold its weight of water 

 from 50 to 2 1 2. 



By this standard of mechanical action for pro- 

 ducing vibration of particles of water, estimates 

 have been made, in equivalent foot-pounds, of the 

 amount of heat required to convert a pound of ice 

 into steam. Taking as a basis the force required 

 to raise the temperature of one pound of water i 

 Fahr. (Joule's equivalent), the following calcula- 

 tions have been made : 



To excite vibration of the particles of i Ib. of ice to 



the degree of liquidity, requires 110,396 foot Ibs. 



To excite i Ib. of water from 32 to 212, that is, 



180 of increase of heat X 772 foot Ibs., requires . 138,960 foot Ibs. 



To excite i Ib. of water at 212 into steam, that is 967 



X 772 foot Ibs. requires 746,524 foot Ibs. 



The total mechanical action of 995,880 foot Ibs. 



is therefore the equivalent of the heat requisite to 

 convert one pound of ice into steam ; which being 

 divided by 33,000 = 30^ horse power. 



This theoretical estimate exhibits the wonderful 

 extent of mechanical action transmitted by the vi- 

 bratory motion of the electric medium as sunshine. 



The force required to convert one pound of 

 water from its gases to ice, has been compared to 

 the descent of a ton down three precipices with a 

 total fall of 2,850 feet. 1 



1 " Heat as a mode of Motion," p. 168. The " latent heat of evapora- 

 tion of I Ib. of water, from and at 212," is given by Mr. Rankine (Treat- 



