298 



EBULLITION. 



In fact, the liquid has, by the process of boiling, been converted into vapor 

 or steam, which is a body similar in its leading properties to common air, and, 

 like it, is invisible. It will hereafter appear that it likewise possesses the 

 property of elasticity and other mechanical qualities enjoyed by gases in gen- 

 eral. ' 



Again, let an open vessel be filled with water at 60°, and placed in a mer- 

 curial bath, which is maintained by a fire or lamp applied to it at the tempera- 

 ture of 230°. Place a thermometer in the water, and it will be observed grad- 

 ually to rise as the temperature of the water is increased by the heat which it 

 receives from the mercury in which it is immersed^ The water will steadily 

 rise in this manner until it attains the temperature of 212° ; but here the ther- 

 mometer immersed in it will become stationary. At the same time the water 

 contained in the vessel will become agitated, and its surface will present the 

 same appearance as if bubbles of air were rising from the bottom, and issuing 

 at the top. A cloudy vapor will be given off in large quantities from its sur- 

 face. This process is called ebullition or boiling. If it be continued for any 

 considerable time, the quantity of w^ter in the vessel will be sensibly dimin- 

 ished ; and at length every particle of it will disappear, and the vessel will 

 remain empty. During the whole of this process, the thermometer immersed 

 in the water will remain stationary at 212°. 



Now, it will be asked, what has become of the water 1 It cannot be im- 

 agined that it has been annihilated. We shall be able to answer this by adopt- 

 ing means to prevent the escape of any particle of matter from the vessel con- 

 taining the water into the atmosphere or elsewhere. Let us suppose that the 

 top of the vessel containing the water is closed, with the exception of a neck 

 communicating with a tube, and let that tube be carried into another close ves- 

 sel removed from the cistern of heated mercury, and plunged in another cistern 

 of cold water. Such an apparatus is represented in fig. 1. 



Fig. 1. 



A is a cistern of heated mercury, in which the glass vessel B, containing 

 water, is immersed. From the top of the vessel B proceeds a glass tube C 

 inclining downward, and entering a glass vessel D, which is immersed in a cis- 

 tern E of cold water. If the process already described be continued until the 

 water by constant ebullition has disappeared, as already mentioned, from the 

 vessel B, it will be found that a quantity of water will be collected in the ves- 

 sel D ; and if this water be weighed, it will be found to have exactly the same 

 weight as the water had which was originally placed in the vessel B. It is, 

 therefore, quite apparent that the water has passed by the process of boiling 

 from one vessel to the other ; but, in its passage, it was not perceptible by the 

 sight. The tube C and the upper part of the vessel B had the same appear- 

 ance exactly as if they had been filled with atmospheric air. That they are 

 not merely filled with atmospheric air in the vessel, may, however, be easily 

 proved. When the process of boiling first commences, it will be found that 

 the tube C is cold, and the inner surface dry. When the process of ebullition 



