Experiments on the Latent Heat of Steam. 39 



The experiment is carried out as follows : — 

 The liquid is introduced into the boiler, the two portions 

 of the apparatus are fitted together, and the screens, etc., 

 properly arranged. The burner is then lighted, and the 

 thermometer in the calorimeter is read at intervals of a minute, 

 until the experiment is concluded. The moment when the 

 liquid is observed to boil marks the end of the ' preliminary 

 period,' and up till this time the march of the thermometer 

 per minute has been small ('02° to '03°, or less). The liquid 

 is then allowed to boil until the rise of temperature pro- 

 duced by the condensation is thought to be sufficient. At 

 this point the flame is extinguished, the boiler is removed, 

 and the condensing worm is corked up. After a short time 

 the march of the thermometer again becomes slow and 

 regular, and during this final period is " exactly the same as 

 that of a thermometer placed in the same calorimeter, filled 

 with the same quantity of water taken at the final temper- 

 ature, but without any previous heating of the screens ; a 

 march carefully ascertained by preliminary experiments." 

 (Mec. Chim. I., p. 294.) 



Now let us see how the latent heat of steam can be 

 deduced from these observations. 



If L = the latent heat of steam for the temperature T, 

 at which the water boils under the pressure pre- 

 vailing at the time of the experiment ; 



W = the weight of water condensed ; 



w = the calorific equivalent of the calorimeter and its 

 contents at the beginning of the experiment ; 



/ = the initial temperature of the calorimeter at the 

 beginning of the condensation ; 



^=the final temperature which the calorimeter would 

 possess if no heat were lost or gained except 

 that due to the condensation of the steam ; 



