180 



HEAT. 



536-6, and therefore he concluded that the results obtained from it with 

 other liquids were trustworthy. 



Regnault made a series of determinations of the latent heat of steam 

 at various temperatures, using at higher temperatures a boiler in which 

 the pressure could be maintained at any desired value, so that the boiling- 

 point could be regulated. From this the steam, still at the same tem- 

 perature, was led into a spiral in a calorimeter, where it was condensed 

 and the heat given out was measured (Jamin, ii. 243). By subsidiary 

 experiments he determined the corrections for conduction and radiation. 



At lower temperatures the water 

 was contained in a spiral immersed 

 in a calorimeter, and the pressure 

 was reduced to the point at which 

 the water boiled. The vapour was 

 led off and condensed in a vessel 

 surrounded by ice, and the heat 

 given up was there measured. 

 Regnault put his results in the 

 following form : Calling the heat 

 required to raise 1 gm. of water, 

 from to *, and then to convert 

 it into saturated steam at f the 

 " total " heat of the steam at *, and 

 denotingit by Q,Regnaultfoundthat 

 Q = 606-5 + 0-305*. 



Taking no account of the alteration 

 in the specific heat of water with 

 rise of temperature, we have 



Hence, 



L = 606-5 + 0-305*-* 

 = 606-5 -'695*. 



FIG. 105. Berthelot's Apparatus for 

 Latent Heat. 



From this we see that the latent 

 heat decreases as the temperature 

 rises, another indication that the 

 liquid and gaseous conditions are 

 approaching each other. 



Regnault's formula for the total heat of steam gives the latent heat 

 at 0., L = 606-5. Winkelmann (Wied. Ann., 9, 1880), re-examining 

 Regnault's work, showed that the values obtained from the formula at 

 low temperatures are probably higher than his experimental results 

 warrant, and Dieterici (Wied. Ann., 37, 1889) made a direct determina- 

 tion of L by boiling water at in a Bunsen calorimeter and measuring 

 the volume of ice formed by the subtraction of a given weight of 

 vapour. He obtained L = 596 -8. 



Griffiths (Phil. Trans., A., 1895, Part I., p. 261) devised a new method 

 of determining the latent heat of steam, and used it for the two tempera- 

 tures of 30 and 40 0. A small glass tube, open at one end and con- 

 taining a known weight of water, was fixed in an exhausted silver flask 

 immersed in a calorimeter containing oil. The water issued from the 



