mi: TIIKKMMPYNAMICAI. PROPERTIES OF SUPERHEATKI* -II:\M 25 



is exhausted, wlien the steam suddenly follows the law of gases. It should be 

 remembered, however, that in the actual experiments the wetness of the steam in 

 the steam chest from which the steam supply is taken was altered as much as possible 

 in different experiments under the sain*- initial pressures and temperatures, but it was 

 not found possible to affect the apparent dryness of the steam just before entering the 

 orifice by an amount which came within the limits of oljservation, it being here noted 

 that if the dryness fraction of the steam before entering the orifice had been altered 

 by so little as 0'06 per cent, (the temj>erature of saturation being 284 F.), a difference 

 of 1 F. would have been observed in the temperature of the wiredrawn steam, a 

 quantity which would at once have been observed. 



The experiments, therefore, indicate that even after relieving the steam of moisture 

 by gravitation, there is still an effect as if a small quantity of moisture were present 

 in the steam. 



The curve representing the pressure temj,>erature relation in the steam wiredrawn 

 from a definite initial condition coincides for a short distance with the curve 

 representing the law of saturation in Diagram 5, and the length of the coincident 

 portions varies with the initial temperature of the steam, the approximate fall of 

 temjjerature during the coincidence of the curves being represented by the following 

 table :- 



Initial temperature Fall of temperature before the 



of saturation. gaseous condition is established. 



239-2 F. 2-8 F. 



239-8 2-8 



261-5 47 



262-0 47 



284-0 '5-5 



298-9 6-6 



345-15 9-15 



379-5 10-5 



Taking the first row in this table, it would appear that saturated steam wiredrawn 

 down till it first becomes gaseous at 236*4 possesses a total heat of gasification under 

 constant pressure identical with the total heat of evaporation of dry saturated steam 

 at 239-2, and, further, that dry saturated steam at 236 "4 is not steam gas, but 

 possesses what is equivalent to a dryness fraction of 99*91 per cent. In a similar 

 manner dry saturated steam (as defined at the commencement of this pa}>er) at 

 369 F. would apparently have a dryness fraction of 99*63 per cent, to bring it to 

 steam gas. 



Proceeding now to examine the lower ends of these curves of free expansion, it 

 will be noticed that the curvature of the curves is very small and regular, even to 

 pressures of 2*5 Ibs. per square inch absolute. If now these curves lie continued to 

 the zero pressure line as curves of the same curvature throughout (which may or may 



VOL. cxciv. A. E 



