of Water at High Temperatures. 



123 



§ 14. These observations will be found projected in fig. 8, 

 (PL III.) the readings of the water-tube being coordinate with 

 the CM. (Centigrade mercury) temperatures by acid-tube ther- 

 mometer. The thick dotted line is drawn by means of a thin 

 flexible straight edge bent round and held so as to suit the 

 general trend of the points. The vertical dotted lines inter- 

 cepted by the thick dotted line represent the ordinates to each 

 10° of the air-thermometer (C.A.), which were read off by scale 

 as follows : — 



320 C.A. . 



. . 4-486 



260 C.A. . 



. . 2835 



310 „ . 



. . 4-068 



250 „ 



. . 2-660 



300 „ 



. . 3-745 



240 „ 



. . 2-490 



290 „ 



. . 3-455 



230 „ 



. . 2-350 



280 „ 



. . 3-230 



220 „ 



. . . 2-222 



270 „ . 



. . 3023 



210 „ 



. . . 2102 



The value of zero of scale is 6-36, and *04 is half the depth 

 of capillary cup, so that 6*4 added to each ordinate gives abso- 

 lute liquid volume at each 10° of the air thermometer. The 

 reading at 4°, the point of unit or minimum volume, is 0*89, to 

 which adding 6*4 gives 7"29, the absolute liquid volume at 

 4°. If there was no correction required for expansion of glass 

 and the density of vapour in the upper part of the tube, the 



6-4 + 4-486 10-886 , 



quotient - = - would represent the volume ot 



water at 320° C.A. in terms of volume unity at 4°. If the glass 

 that contained the 7'29 of water were to assume the volume it 

 has at 320°, the apparent volume 7*29 would be diminished 

 -047, [7r] being at the rate of y^jth per 100°, which has been as- 

 sumed as a probable value. Again, if we find the volume that 

 the steam in the upper part of the tube would obtain if condensed 



1 0*886 



to water at 4° and call this y. then —7-^ — ; r is the true 



y ' 7-29 — (7r + y) 



volume at 320° To find y, the whole contents of the tube is 



12-33, from which taking 10*89, leaves 1-44. The density of 



steam at t is expressed by the formula < — - > = D, which 



rests on Regnault's observations and the law of vapour-density 

 (see Phil. Mag. March 1858, Appendix I., and June 1861, § 11). 

 The density of steam at 100° in terms of water-unity at 4° being 



•00061337, we have | 1QQ + 76 ' 8 \ 6 = -00061337, and hence 



log A x =2-78296. 



Thus D for * = 320 is S^±J^\ b = 0-109, and this, 



multiplied by 1-44 the volume of top space, gives y — 0*157, 



