CHANGE OF STATE LIQUID VAPOUR. 



th 



tubes were filled with oil or mercury, and thermometers were inserted 

 which gave the temperature. As the indications of the four agreed, the 

 boiling was normal and not " with bumping." 



It was found that on altering the pressure in G, the temperature 

 soon reached a steady state, the boiling-point at the pressure indicated 

 by the manometer. The manometer, therefore, gave the pressure of 

 the vapour at the observed temperature. 



For temperatures above 150, the apparatus employed was exactly 

 the same in principle, but much larger and stronger, and Regnault 

 was able to work with it up to 230 at a pressure above 27 at- 

 mospheres. 



The vapour-pressures of various other liquids have also been deter- 

 mined for a series of temperatures by Regnault and other observers 

 using similar methods. 



An account of the various methods will be found in 

 Winkelmann's Handbuch der Physik, 2nd ed., vol. iii. p. 

 903. The values obtained for the vapours of water and 

 various other liquids will be found in Landolt-Bbrnstein, 

 Tdbellen, p. 119 et seq. 



Determination of Boiling-Points. The boiling- 

 points of liquids are often required, the knowledge of the 

 vapour-pressure at other temperatures not being needed. 



If the liquid whose boiling-point is in question is 

 plentiful, it may be heated to boiling in a flask, or the 

 apparatus used in determining the 100 point on the 

 thermometers may be used, care being taken that the 

 boiling is normal. A very simple arrangement, using the 

 statical method, is that illustrated in Fig. 99. 



AB is a U tube. The shorter limb is closed, and is 

 filled with mercury, which extends just round the bend. 

 A small quantity of liquid is then introduced, and by 

 careful manipulation may be floated up through the 

 mercury without any air, so as to occupy the end a of the shorter limb- 

 The tube is then immersed in a bath, which is heated until the vapour 

 forms and depresses the mercury. When the level is the same in both 

 limbs, the vapour-pressure is equal to the atmospheric pressure, and the 

 temperature gives the boiling-point. This method, of course, admits of 

 simple correction for variation of atmospheric pressure. The following 

 are a few boiling-points : 



FIG. 99. 



Ether 

 Alcohol 

 Water 

 Mercury 



34-87 



78-4 



100-0 



358-5 



Determination of Vapour-Density. The method of determining 

 the density of gases at and 760 mm. pressure consists in filling a 

 globe with the gas to be experimented on, at the atmospheric pressure H, 

 while it is surrounded with melting ice ; then closing it and weighing it. 

 The globe is then put into the ice again, exhausted to a low pressure h, 

 closed, and again weighed. Suppose the diminution in weight is W. 



