100 



HEAT OR CALORIC. 



10. Atmospheric pressure opposes and limits chemical action, where 

 elastic fluids are to be generated or evolved. 



" Water would boil at a lower temperature than 212, if the at- 

 mospheric pressure were lessened ; for when it has ceased to boil in 

 the open air, it will begin to boil again in an exhausted receiver ; 

 and those who ascend mountains find, that for every five hundred 

 and thirty feet of elevation, the boiling point is lowered one degree 

 of Fahrenheit's thermometer." 



The boiling point is lowered by a diminution 

 of atmospheric pressure. 



" Water heated to ebullition in a glass ves- 

 sel, having ceased to boil in consequence of its 

 removal from the fire, will boil again under a 

 receiver, as soon as the air is withdrawn." 



1 1 . Boiling point raised by pressure. 



Jls the Boiling Point is lowered by diminution of Pressure, so it is 

 raised if the Pressure be increased. 



" Into a small glass matrass, with a bulb, 

 of about an inch and a half in diameter, 

 and a neck of about a quarter of an inch 

 in bore, introduce nearly half as much 

 ether as would fill it. Closing the orifice 

 with the thumb, hold the bulb over the 

 flame of a spirit lamp, until the effort of 

 the generated vapor to escape, becomes 

 difficult to resist. Removing the matrass, 

 to a distance from the lamp, lift the thumb 

 from the orifice : the ether, previously qui- 

 escent, will rise up into a foam, produced 

 by the rapid extrication of its vapor." 



" This experiment may be performed 

 more securely, by employing a vessel of 

 hot water, instead of a flame, to warm the matras," 



