300 



EBULLITION. 



If a thermometer be immersed in the steam which collects in the upper part 

 of the vessel B, it will show the same temperature (of 212°) as the water from 

 which it is raised. The heat, therefore, received from the mercury is clearly 

 not imparted in a sensible form to the steam, which has the same temperature 

 in the form of steam as it had in the form of water. The result of investiga- 

 tions respecting liquefaction would lead us, by analogy, to suspect that the 

 heat imparted by the mercury to the water has become latent in the steam, and 

 is instrumental to the conversion of water into steam, in the same manner as 

 heat was formerly found to be instrumental to the conversion of ice into water. 

 As the fact was in that case detected by mixing ice with water, so we shall, in 

 the present instance, try it by a like test, viz., by mixing steam with water. 

 Let about five and a half ounces of water, at the temperature of 32°, be placed 

 in a vessel A (fig. 2), and let another vessel, B, in which water is kept con- 

 Tig. 2. 



stantly boiling at the temperature of 212°, communicate with A by a pipe C 

 proceeding from the top, so that the steam may be conducted from B, and es- 

 cape from the mouth of the pipe at some depth below the surface of the water 

 in A. As the steam issues from the pipe, it will be immediately reconverted 

 into water by the cold water whifth it enters ; and, by continuing this process, 

 the water in A will be gradually heated by the steam combined with it and 

 received through the pipe C. If this process be continued until the water in 

 A is raised to the temperature of 212°, it will boil. Let it then be weighed, 

 and it will be found to weigh six and a half ounces ; whence we infer that one 

 ounce of water has been received from the vessel B in the form of steam, and 

 has been reconverted into water by the inferior temperature of the water in A. 

 Now, this ounce of water received in the form of steam into the vessel A had, 

 when in that form, the temperature of 212°. It is now converted into the liquid 

 form, and still retains the same temperature of 212° ; but it has caused the five 

 and a half ounces of water with which it has been mixed, to rise from the tem- 

 perature of 32° to the temperature of 212°, and this without losing any tempera- 

 ture itself. It follows, therefore, that, in returning to the liquid state, it has 

 parted with as much heat as is capable of raising five and a half times its own 

 weight of water from 32° to 212°. This heat is combined with the steam, 

 though not sensible to the thermometer ; and was, therefore, latent. Had it 

 been sensible in the water in B, it would have caused the water to have risen 

 through a number of thermometric degrees, amounting to five and a half times 

 the excess of 212° above 32° : that is, through five and a half times 180° ; for 

 it has caused five and a half times its own weight of water to receive an equal 

 increase of temperature. But five and a half times 180° is 990°, or, to use 

 round numbers (for minute accuracy is not here our object), 1,000°. It follows, 

 therefore, that an ounce of water, in passing from the liquid state at 212° to 

 the state of steam at 212°, receives as much heat as would be sufficient to 

 raise it through 1,000 thermometric degrees, if that heat, instead of becoming 

 latent, had been sensible. 



