402 



Scientific Proceedings, Royal Dublin Society. 



funnel, a \ery little mercury beiug first introduced in order to prevent the 

 liquid from coming in contact with the india-rubber tube, E. 



The volume-tube is at first placed 

 in the position shown in fig. 8, with 

 the level of the liquid in the tube 

 below the condensed liquid, B, in tlie 

 jacket. The liquid in the bulb, C, 

 is then boiled— with the pressure 

 rather lower than that correspond- 

 ing to the lowest temperature re- 

 quired — and when the vapour has 

 reached the condenser,^ D, the 

 volume-tube is slowly pushed up 

 through the india-rubber tube, E, 

 until the whole of the liquid in it is 

 well above the surface of the con- 

 densed liquid, B. The little tube, F, 

 may then be pushed down, as the 

 water is no longer required. The 

 sealed tube is easily centred by 

 means of the perforated cork, H, 

 held in position by a clamp and 

 retort-staud. 



After the tube is in position, 

 the pressure is slowly raised until 

 it corresponds to the required tem- 

 perature ; and a reading of the 

 height of the liquid is then taken. 

 A second reading is taken after two 

 or three minutes ; and if the volume 

 of liquid is smaller, readings are 

 taken from time to time until con- 

 stancy is attained. 



At moderate temperatures the 

 volume of liquid should become con- 

 stant almost immediately, but near 

 the critical point the evaporation of 

 the liquid becomes much slower ; 



' For liquids boiling above 160° a condenser is not re(juii-ed ; but it is advisable to use the wide 

 cylindrical glass tube, as described on p. 395. 



H 



Fig. 8. 



and this is especially the case if any 



