7/ Steam at various Temperatures. 361 





Art. XXXI. — On a New Table of the Pressure of Steam at 



various Temperatures ; by J. H. Alexander, Esq. 



In a former Number of (his Journal,* I gave the elements of a 

 new theorem for calculating the tension of Vapor of Water at all 

 temperatures; and presented at the same time an extensive tabu- 

 lated comparison of the indications of this theorem with the re- 

 sults of the best experiments upon the pressure of steam. This 

 comparison, extending between - 27° and +435° of Fahrenheit's 

 thermometer-scale, shewed among other things, that the pressures 

 calculated by the theorem, agreed more closely and consistently 

 ' with the mean of the observations than the experimental numbers 

 did, themselves ; and in so far, therefore, the formula was fully 

 sustained. 



A supplemental Memoir in a succeeding Number.f contained 

 a discussion of the admitted uncertainties of divers experimental 

 series (being also those, accepted as the best contrived and most 

 reliable, hitherto) and of the consequent probable errors by the 

 formula; the reasonable conclusion from all which, was that thi 

 mean probable error of this last is less than the actual contingent 

 (or it may be, necessary) inaccuracies of the experiments ; and 

 therefore, that the reciprocal temperatures and pressures assigned 

 by the theorem, were in fact more thoroughly and safely reliable 

 than the quantities given in any single series of observations. 



Accompanying this last memoir, was a short table whose argu- 

 ment is the pressure of Steam in Atmospheres: and it only re- 

 mained, for completing the subject, to have a corresponding table 

 whose argument should be the temperature in degrees of Fahren- 

 heit. This I have prepared and now present. It extends from 

 zero of Fahrenheit, for every five degrees, up to the melting point 

 of ice ; and progresses thence, from degree to degree, up to 365°, 

 which may be considered as even beyond the limiting tempera- 

 ture for safe or judicious application. The pressures are given in 

 inches of a mercurial column supposed at a constant temperature 

 of 32° P.; but they can be converted into pounds avoirdupois 

 per square inch very readily and with sufficient accuracy for the 

 most of practical purposes, by halving the tabular numbers. The 

 column of differences of elasticity for each degree, which had to 

 be made up as one of the checks upon the arithmetical operation, 

 has been retained and will be found frequently useful. 



ii Ser., vol. vi, p. 210, seqq. f ii Ser. ? vol. vi, p. 317, seqq. 



Second Series, Vol VII, No. 21.— May. 1849. 46 





