6 Mr. J. H. Alexander on the Tetisioji of Vapour of Water. 



mospheric pressure. Then the former, which went altogether 

 towards maintaining the state of vapour, without increasing its 

 apparent temperature, was b'S times the latter; now the latter is 

 h'b times the former. And from this consideration flows an 

 easy manner of connecting proportionate volumes and pressure 

 with simple multiples of the increments of heat. But to deve- 

 lope this here, would be to wander from the present aim. 



If we go on to suppose the temperature increased until the 

 whole of the latent heat is utilized and becomes sensible 

 (which occurs at 1170° F.), we should then have a condition 

 in which steam under a pressure of 4225 atmospheres (by the 

 formula) is reduced to very nearly y'^ths of the unitary volume 

 of water to produce it, and has a density (without regard to 

 the expansion from temperature) 2*5 times that of water at its 

 maximum. The expansion due to the temperature is (with 

 Gay-Lussac's factor) 0"975 of the unitary volume; the ex- 

 pansion of water due to the same temperature (taking its 

 maximum density as occurring at 39°'4 F., its actual expansion 

 as 0'04<333 at 212°* F., and its rational expansion as the cube- 

 root of the fifth power of the temperature above the maximum) 

 is 0'99944 of the same unitary volume — an accord which, 

 considering the possible errors of the experiments, appears to 

 me sufficiently satisfactory. 



The equations already given serve to find the pressures in 

 inches of mercury and in atmospheres respectively, when the 

 temperatures are given : to find the temperatures correspond- 

 ing to given pressure, they become as follows : 



/=180 Vp — 105°-13; 

 where/? represents the number of inches of mercury; and 



/ = 307-13 Vy'-lOS^-lS; 

 where/)' stands for the number of atmospheres. 



After these preliminaries, may now be presented the com- 

 parison of results by the formula and by the experiments of 

 various observers ; as is done in the following table. This 

 table is quite extensive; and, for my own sake, rather more so 

 than I desired. But it will be considered that it comprehends 

 the assemblage of the observations of many persons through 

 many years ; and it was, besides, to me of an interest that I 

 think will be partaken of by others, to have in one view and 

 without interpolation nearly all the determinations that have 

 been made by actual experiment. In limiting it to statements 

 of this character, I confess I thought at first to restrict its extent, 

 though it appears that there are in fact more experimental 

 data than is generally supposed ; and I desired besides to in- 

 crease its utility beyond the mere comparison with the present 

 formula, by fitting it as a depository for general reference. In 

 this last regard, it may be considered as authentic and reliable. 



