EBULLITION. 



297 



EBULLITION. 



IT is known that the continued application of heat to a solid causes it ulti- 

 mately to pass into the liquid form. We propose, in the present discourse, to 

 examine the effects which would be produced by the continued application of 

 heat to a liquid. 



Let a small quantity of water be placed in a glass flask of considerable size, 

 and then closed so as to prevent the escape of any vapor. Let this vessel be 

 now placed over the flame of a spirit lamp, so as to cause the water it contains 

 to boil. For a considerable time the water will be observed to boil, and ap- 

 parently to diminish in quantity, until at length all the water disappears, and 

 the vessel is apparently empty. If the vessel be now removed from the lamp, 

 and suspended in a cool atmosphere, the whole of the interior of its surface 

 will presently appear to be covered with a dewy moisture ; and at length a 

 quantity of water will collect in the bottom of it equal to that which had been 

 in it at the commencemjnt of the process. That no water has at any period 

 of the experiment escaped from it may be easily determined by performing the 

 experiment with the glass flask suspended from the arm of a balance, counter- 

 poised by a sufficient weight suspended from the other arm. The equilibrium 

 will be preserved throughout, and the vessel will be found to have the same 

 weight, when to all appearance it is empty, as when it contains the liquid 

 water. It is evident, therefore, that the water exists in the vessel in every 

 stage of the process, but that it becomes invisible when the process of boiling 

 has continued for a certain length of time ; and it may be shown that it will 

 continue to be invisible, provided the flask be exposed to a temperature consid- 

 erably elevated. Thus, for example, if it be suspended in a vessel of boiling 

 water, the water which it contains will continue to be invisible ; but the mo- 

 ment it is withdrawn from the boiling water, and exposed to the cold air, the 

 water will again become visible, as above mentioned, forming a dew on the 

 inner surface, and finally collecting in the bottom as in the commencement of 

 the experiment. 



