.s/A 1 \VII.UAM SIEMENS, l-.R.S. 2$ 



approaches so nearly to its asymptote that the difference cannot 

 be detected by experiments. 



The general result obtained from the above experiments may be 

 stated as follows : that steaui generated at 212*, and maintained 

 at a constant pressure of one atmosphere, when heated out of 

 contact with water to 



230 is expanded 5 times more than air would be. 



240 4 



260 3 



370 2 



The author intends to extend the range of his experiments upon 

 gases and vapours under high pi'essure, and will be glad to 

 communicate the further results to the Institution. 



The diagram contains another curve, C, showing the results of 

 Mr. Frost's experiments, alluded to before, which, from the very 

 sudden and irregular rise at the commencement, appears to be 

 affected by some serious source of error. 



The two curves of pressure and density, P and D, show the rate 

 at which saturated steam increases in pressure and in density, with 

 the rise of temperature marked at the bottom of the diagram. It 

 will be observed that the pressure increases at a rather greater rate 

 than the density ; and it is a remarkable circumstance, that the 

 difference, or the rate at which the pressure increases faster than 

 the density, which is in effect the rate of expansion of saturated 

 steam with the increase of sensible temperature, exactly coincides 

 with the line B, representing the rate of expansion of atmo- 

 spheric air. 



An extension of our knowledge on the properties of steaui is a 

 matter of such evident importance to engineers, that it would be 

 useless to dwell upon its practical importance. Suffice it to say, 

 that it has been theoretically demonstrated that a perfect Boulton 

 and Watt Condensing Engine (abstracting friction and all losses of 

 heat in the furnace and through radiation) would only yield about 

 seven per cent, of the mechanical force which would be equivalent 

 to the expended heac. It may be argued from this, that the 

 steam engine is destined to undergo another great modification in 

 principle, and in the author's humble opinion this crisis will be 

 accelerated by inquiries into those properties of gaseous fluids 

 which have hitherto excited but little attention, and especially 

 into the properties of dry steam, or isolated steam. 



