DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 279 



" Zu Beginn des dritten Tages versagte der Apparat seinen Dienst und 

 es war infolge der durch die starke Hitze eiutretenden allmiihlichen 

 Veranderungen des Materials und inbesondere infolge der Abnutzung 

 des Hahnes H nicht wieder der erforderlicbe Grad der Dichtheit zu 

 erreicbeu." If a small leak of tbe same sort bad been present witbout 

 being noticed on tbe two days on wbicb observations were made, its 

 effect would bave been to make tbe observed L too large, just as it 

 seems to be. At any rate, tbe point at 180° is not entitled to nearly 

 as mucb weigbt as tbe otbers. Tbe point at 140° was, bowever, as far 

 as Henning could j udge, as good as any of tbe rest. 



One otber aspect of Henning's paper tends to minimize tbe signifi- 

 cance of tbe disagreement at tbe two bigb temperatures. He is led by 

 bis points at 140° and 180° to tbe conclusion tbat tbe curve L =f(t) 

 is a straight line between 120° and 180°. Now, of course, it is pos- 

 sible tbat be and Regnault are both rigbt in finding unexpectedly 

 higb values near 180°, and tbat, because of changing polymerization 

 or some other disturbing condition, tbe character of the curve L =f(t) 

 between 120° and 180° is very different from that which it is known 

 to have below 120° and from that which it must begin again to have 

 somewhere above 180°, if it is to come vertically to zero at the critical 

 temperature as is commonly supposed. This is, however, not probable, 

 and until Henning's 180° point is definitely verified by observations 

 with unquestionable apparatus, the writer will still believe that the 

 formula proposed in this paper is nearer the truth than is Henning's 

 straight line. The excellence of the confirmation between 65° and' 

 121° and also at 160° seems more significant than the disagreements 

 at 140° and 180°. 



Another check of the new H formula can be obtained by computing 

 from it tbe specific volume of saturated steam by means of Clapyron's 

 equation 



- '4- T L 1 



V V ±J T(dp/dvU' 



This check has been carried through independently by Peabody 24 and 

 by the writer. 25 In both cases the necessary values ofdp/dt were taken 

 from the recent paper of Holborn and Henning on the saturation pres- 

 sures of steam, 26 and the values of L were based on the formula pro- 

 posed in this paper. The choice of a suitable value for H WQ and of 

 suitable values for the heat of the liquid which has to be subtracted 



24 Proc. Am. Soc. Mech. Engs., 1909, 31, 595. 

 29 Marks and Davis, Steam Tables. 

 26 Wied. Ann., 1908, 26, 833. 



