508 



Dr. W. C. McG. Lewis on the Nature of the 



Table.) The values of the latent heat are those of Winkelmann, 

 Wied. Ann. ix. p.c 83S '(iggf))." \ 



It will be' sfcen that cf s ■ and" rr n converge slightly with 

 rising temp"era*ture. This convergence no doubt becomes 

 abrupt as we approach* the" tfrstical temperature, where of 

 course j^W^er^? r '«. / S ■ - . \ . 



The IrubemUl yPf t $£m / r&2®£ c°W&tejr?f4 thi bulk of the liquid 

 and in the 1 surface' \ laver*, '■ and its variation with 

 Temperature. 



Having obtained values for the specific volumes in the 

 surface-layer and bulk, we calculate the corresponding- 

 internal pressures by equation (1) or (2). The results are 

 given in the following Table. I have here calculated the 

 values of K to and K 5 , first assuming that van der Waals* 

 constant a has the value 0*0107 (and remains constant) ; 

 secondly, a is assumed to be 00178, its value for the critical 

 temperature. The values of K TO and K^ are no doubt far 

 from the truth when calculated on the second assumption, 

 since the temperature range 0-100° C. is fairly far removed 

 from the critical region (364° C). Comparison is, however, 

 instructive as showing how the want of constancy in a is 

 magnified when applied to internal pressure values. If a 

 were really constant, K s and K w should vary only as the 

 respective specific volumes. 



Table III. — Internal Pressure of Water at different 

 Temperatures. 



Temperature, 

 0°C. 



V - a 



v m 

 (a=0-0107). 



(a=0-0107). 



TT a 



K m= 7-3 



(«=0-017S). 



(a=0'0178). 





atmospheres. 



atmospheres. 



atmospheres. 



atmospheres. 



3-61 



10,700 



51,260 



17,810 



30,800 



13-95 



10,650 



50,350 



17,720 



30,260 



25-14 



10,640 



49,320 



17,700 



29,630 



37-31 



10,560 



48,060 



17,560 



28,880 



5064 



10,450 



46,510 



17,390 



27,960 



6536 



10,290 



44,790 



17,120 



26,920 



81-71 



10,080 



42,600 



16,770 



25,630 



1000 



9,840 



41,290 



16,370 



24,210 



