HEAT OR CALORIC. 101 



12. Column of Mercury raised by vaporized Ether. 



Jin increase of Pressure results from constrained 

 Ebullition. 



" Having supplied a small flask with a little 

 mercury, and a minute portion of sulphuric 

 ether : through the neck, let there be a glass 

 tube, so introduced, and firmly luted, as that it 

 may be concentric with the vertical axis of the 

 vessel, and extend downwards until nearly in 

 contact with the bottom. If the flask thus pre- 

 pared, be held cautiously over a spirit lamp, the 

 ether will be more or less converted into vapor. 

 The vapor being unable to escape, will soon 

 cause the mercury to rise to the top of the tube. 

 On the removal of the lamp, the mercury gradu- 

 ally falls to its previous situation." 



It is better, as Dr. Hare has before recom- 

 mended, to plunge the flask cautiously into hot 

 water (of about 150', or 180,) as the pressure 

 sometimes blows out the bottom of the flask, 

 when, if over fire, a dangerous combustion would 

 ensue. 



13. HIGH PRESSURE BOILER. 



That the temperature of Steam is directly as the pressure, may be 

 demonstrated by a small Boiler, such as is represented in the fol- 

 lowing cut. 



" The glass tube in the axis, passes below the water in the boiler, 

 and enters a small quantity of mercury at the bottom. The junc- 

 ture of the tube, where it enters the boiler, is made perfectly tight. 

 On the opposite side of the boiler, a tube, not visible in the draw- 

 ing, descends into it. This tube consists of about two inches of a 

 musket barrel, and is closed at bottom. The object of it is to 

 contain some mercury, into which the bulb of a thermometer may be 

 inserted, for ascertaining the temperature." 



" When the fire has been applied during a sufficient time, the 

 mercury will rise in the glass tube, so as to be visible, above the 

 boiler ; and continuing to rise, during the application of the fire, it 

 will be found that with every sensible increment in its height, there 

 will be a corresponding rise of the mercury in the thermometer. 

 In front of the tube, as represented in the figure, there may be ob- 

 served a safety valve, with a lever and weight, for regulating the 

 pressure." 



