22 PROPERTIES OF STEAM AND OTHER VAPORS. 



square foot, the volumes in cubic feet per pound, and tin- temperatures 

 in the Fahrenheit scale, we have 



fv - 85.85 T - p (i + 0.00000976 p) ('50.300,000 



The following equation may be u>ed with the jin un in pounds per 

 square inch: 



fv - 0.596* T-HI+ 0.0014 p) ( r 5'30o.ooo _ Q 



The labor of calculation is principally in reducing the corrective term, 

 and especially in the computation of the factor containing the tempera- 

 ture. Table XV gives values of this factor for each five degrees from 

 100 to 600 F.; the maximum error in the calculation of volume by aid 

 of the table is about 0.4 of one per cent at 336 pounds pressure and 428 

 F.; that is at the upper limit of our table for saturated steam. At 150 

 pounds and 358 F., which is about the middle range of our table for 

 saturated steam, the error is not more than 0.2 of one per cent, which is 

 not greater than the probable error of the equation itself under those 

 conditions. At lower pressures and at higher temperatures the error 

 tends to diminish. 



The following simple equation is proposed by Tumlirz * based on 

 experiments by Battelli. 



fv = BT - C pt 



where p is the pressure in kilograms per square metre, v the specific 

 volume in cubic metres, and T the absolute temperature Centigrade. 

 The constants to agree with Knoblauch's work should be 



B = 47.10, C = 0.016. 



In the English system with the pressure in pounds per square foot and 

 the volumes in cubic feet, for absolute temperatures Fahrenheit, 



pv = 85.85 T - 0.256 p. 



This equation has a maximum error of 0.8 of one per cent as compared 

 with Knoblauch's equation. 



Specific Heat. Two investigations have been made of the specific 

 heat of superheated steam at constant pressure, one by Professor 

 Knoblauch f and Dr. Jakob and the other by Professor Thomas 



* Math. Naturw. Kl. Wien, 1899, Ha S. 1058. 



f Mitteilungen uber Forschungsarbciten Heft 36, p. 109. 



