III. On Methods of Determining the Dryness of 

 Saturated Steam and the Condition of Steam Gas. 



By Osborne Reynolds, M.A., LL.D., F.R.S. 



Received October 20th. Read November 3rd, 1896. 



When, after all air has been expelled from a vessel 

 partially filled with water and kept at rest at a constant 

 temperature, equilibrium is established, the vapour is said 

 to be dry saturated steam. 



It is easy to show that under these circumstances the 

 pressure of the steam is a definite function of the tem- 

 perature. But it has been found very difficult to show, 

 by direct means, that the density of the steam is also an 

 invariable function of the temperature, although many 

 experiments, from the time of Watt, have indicated that 

 this is the case; those of Fairbairn and Tate being the 

 least open to criticism. 



That the density of dry saturated steam is a constant 

 function of the temperature has, however, been com- 

 pletely established indirectly by the experiments of M. 

 Regnault on the total heat of evaporation, although 

 these experiments do not directly furnish a measure 

 of the density. These experiments consisted in main- 

 taining a vessel containing a definite quantity of water 

 in steady constant condition as to temperature and 

 pressure and quantity of water, by the steady admission 

 of water at any constant temperature, and the withdrawal 

 of the vapour in an upward direction, with a slow motion 

 so as to preclude the convection of water out of the vessel 



Nov. 77, 1896. 



