2o2 Royal Society. 
expansion between 174°'92 and 180° is ;4,, or three times that of 
air; whereas between 180° and 200° the coefficient is very nearly the 
same as that of air (steam= 4, air=;4,), and so on in other cases. 
The mean coefficient of expansion at zero of temperature from seven 
experiments below the pressure of the atmosphere, and calculated 
from a point several degrees above that of saturation, is -}_, whereas 
for air it is ;15. Hence it would appear that for some degrees 
above the saturation point the steam is not decidedly in an aériform 
state, or, in other words, that it is watery, containing floating vesicles 
of unvaporized water. 
Table of Results, showing the relation of density, pressure, and 
temperature of saturated steam. 
Pressure ~ Specific Volume. Pronarienc 
ee if in Ibs.per,in inches of of saturation From enor > 
; sq. in. | mercury. Fahr. experiment, Hy formula @)) ona 
(e} 
1 2°6 5°35 | 136-77 8266 8183 Sing 
2 4°3 8°62 1ao°3a 5326 5326 0 
3 4°7 945 | 159:36 4914 4900 ae 
4 6°2 12°47 170°92 3717 3766 + 7k 
5 6°3 12°61 171°48 3710 3740 es 
6 6'8 13°62 174°92 3433 3478 + 7s 
7 8-0 16°01 182:30 3046 2985 — sy 
8 i 18°36 188°30 2620 2620 0 
9 13 22°88 198°78 2146 2124 — 37 
EY 26°5 53°61 242-90 941 937 —saE 
ae 27°4 55°52 244°82 906 906 0 
3’ | 276 | 55°89 | 245-22 891 900 rete 
4' 30° 1 66°84 255°50 758 798 0 
5' | 87:8 | 76°20 | 263-14 648 669 ote 
6' 40°3 81°53 267°21 634 628 —st0 
e 41°7 84°20 269°20 604 608 ++t5 
8' 45°7 92°23 274°76 583 562 — sy 
9' 49-4 99°60 279°42 514 519 +343 
11’ 51°7 104°54 282°58 496 496 0 
12’ 55°9 112°78 287°25 457 461 ++ 
13' | 60°6 | 122°25 | 292-53 432 428 uke 
14' 56°7 114°25 288°25 448 456 + sg 
Adopting the notation previously employed, and putting 7 for the 
rate or coefficient of expansion of an elastic fluid at ¢, temperature, 
we find Vv 
- as pals 
ee Se HY 9 . ° e . . (4.) 
Fe obey see 
1 , 
where — = the rate of expansion at zero of temperature. In the case 
2) 
1 
of air e,= 459. 
The following Table gives the value of the coefficient of expansion 
of superheated steam taken at different intervals of temperature from 
the maximum temperature of saturation. 
