THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JULY 1865. 



I. On the Law of Density of Saturated Steam expressed by a New 

 Formula. By ThOxAias Rowe Edmonds, B.J. Cantab.* 



THE expansive force of a unit weight of saturated steam, 

 according to temperature, is usually measured by the pro- 

 duct of the pressure P in pounds to the square foot, multiplied 

 by the volume V in cubic feet occupied by one pound weight of 

 such steam. The product PV represents the work done or re- 

 sistance overcome in foot-pounds, and is equal to the effect pro- 

 duced by a constant force P pounds driving a piston, whose area 

 is one square foot, through the linear space represented by the 

 number which expresses V in cubic feet. When the laws of 

 pressure and volume are both known, the law of expansive force 

 represented by the product PV will be known also. But such a 

 compound will not be entitled to the appellation of a third law, 

 if the two formulae for P and V, when united, do not yield for 

 result a third formula equal in simplicity to either of the two 

 constituent formulae. 



The pressure P of saturated steam appropriate to every tem- 

 perature, from —30° to +230° Centigrade, has been satisfac- 

 torily and accurately determined through the observations of M. 

 Regnault, published in the year 1847. The law of pressure 

 deduced from these observations has been investigated in the 

 Philosophical Magazine for March 1865, and the formula indi- 

 cating the law has been found to be 



hyp.lo g P=^{l-(l + £)-}. 



This formula was directly obtained from the Table of pressures 

 adopted by M. Regnault, through observing that the differentia] 

 * Communicated by the Author. 

 Phil Mag. S. 4. Vol. 30. No. 200. July 1865. B 



