HEAT OR CALORIC. 91 



(T.) " The same weight of steam contains, whatever may be its 

 density, the same quantity of caloric ; its latent heat being increased, 

 in proportion as its sensible heat is diminished ; and the reverse."* 

 Henry. Water distilled in vacuo at 70, gave a vapor which, when 

 condensed, indicated latent heat amounting to 1200 or 1300. 

 Hence there is no economy of heat in distilling in vacuo, for, as the 

 sensible heat is diminished, the latent heat is increased. 



(U.) But steam formed at temperatures above 212, suffers a di- 

 minution of latent heat by the increase of its sensible heat.^ Hence 

 there is no economy of fuel in the use of high steam, for more heat 

 passes off by the chimney than where low steam is generated. There 

 may be convenience and economy of room and money, in the ar- 

 rangements of the machinery, and obviously the higher the temper- 

 ature at which the steam is formed, the more of it there is in a given 

 space, or the more water in the state of steam, and consequently the 

 greater is the moving power. 



(V.) Fluids under vast pressure, maybe converted into vapor with 

 only a small augmentation of volume. This was done by M. de la 

 Tour,{ in glass tubes ; alcohol of thesp. gr. .837, and occupying about 

 | of the capacity of the tube, became transparent vapor by expand- 

 ing to a little over three times its first volume, and with a pressure of 

 119 atmospheres, or 785 Ibs. on the square inch; the temperature 

 was 404.6 Fahr. 



Ether at 369 of Fahr. became vapor, under 38 or 39 atmos- 

 pheres = 576 Ibs. to the square inch, and the vapor occupied less room 

 than that of alcohol or naptha. 



Water, with a trace of carbonate soda, required a little over four 

 volumes to become vapor. In these experiments, the presence or 

 absence of atmospheric air made no difference, and on cooling the 

 tubes, the fluids reappeared, the vapor being condensed. 



At these high temperatures, water can decompose glass, by sepa- 

 rating its alkali, and thus causing the glass to become cloudy. 



* That is, e converse, as the sensible heat increases, the latent heat diminishes, so 

 that equal weights of steam incumbent over water, at whatever temperature, contain 

 the same quantity of heat; or the total heat of steam is a constant quantity. A giv- 

 en quantity of vapor of the same substance, whatever may be its temperature, and 

 e-lasticitj imparts to cold water the same quantity of heat 



t Manchester Memoirs, Vol. II, now series. Brewster's Edit, of Prof. Robinson's 

 works. 



; Annales de Chimie and de Physique, XXI. 127178. XXII. 400. Annals of 

 Philos. V. 290. 



