82 Mr. J. H. Grindley. An ExperimentM I'mestigation of 



from a knowledge of those of saturated steam already obtained by 

 Eegnault. 



The temperature and pressure of saturated steam in a steam chest 

 in which a constant supply of steam is kept is taken, the steam is then 

 drawn upwards to an orifice, and, after wiredrawing, its pressure and 

 temperature are again taken, using for the determination of the latter 

 a thermo-electric junction immersed in the steam. 



Special precautions were found necessary, and special apparatus 

 designed to prevent losses of heat by radiation from the channel con- 

 taining the wiredrawn steam, a steam jacket of peculiar construction 

 enveloping this channel completely, and by adjusting the temperature 

 of the jacket to ec[uality with that in the wiredrawn steam, all radia- 

 tion was effectively prevented from this portion of the apparatus. 



Again, communication of heat from one side to the other of the 

 orifice through the substance in which the orifice is made was pre- 

 vented, and true adiabatic flow obtained through the orifice by drilling 

 it in a piece of plate glass, such as that described in the research on 

 the law of flow through orifices. 



During an experiment, the pressure in the steam chest being kept 

 constant, a series of temperature readings at various values of the 

 lower pressure were observed in the wiredrawn steam. By this means 

 a curve showing the cooling of the steam for any degree of wiredrawing 

 from an initial constant pressure could be drawn on a pressure-tempera- 

 ture diagram. 



Provided now that the total heat of steam before passing the orifice 

 was known, it would be possible to deduce from these temperature and 

 pressure results the values of the mean specific heat at constant pressure 

 of superheated steam between the saturated condition and the tempera- 

 ture of the wiredrawn steam at any given pressure, and further, the 

 total heat of steam at any pressure and temperature obtained by such 

 wiredrawing, would be known. 



Whether the steam was in the same condition before wiredrawing 

 as that obtained in Eegnault's experiments was certainly not an easy 

 point to decide. In both cases, however, the steam A\as obtained by 

 draining any suspended moisture from steam initially wet, but whether 

 this process of drainage always brought the steam into the same con- ■ 

 dition as to dryness, whatever the degree of wetness originally in the 

 steam, was as yet an open question, which could only be decided by 

 experiment. Accordingly experiments were conducted with saturated 

 steam at a known pressure and temperature in the steam chest, but at 

 diff'erent degrees of wetness in difl'erent experiments. The results 

 obtained are very important, as the maximum difference of temperature 

 at any particular pressure in the wiredrawn steam which could be 

 found to exist 1)etwern experiments with different degrees of wetness 

 in the steam in the steam chest was 0*35'' F., and generally the differ- 



