Relation to Presmn and Temperature, 509 



38. ( 'ondusion. — Summarizing these results it appears that 



the exponential v V=ln(\ +ap) ' is more in keeping with the 

 general character of the isothermals discussed than is the hy- 

 perbolic form v/V=up/(l+vp), Botli equations apparently 



fail at 310°. It is difficult to assign a reason for this. It is 

 not probably due to occluded air, since the substances were 

 boiled and introduced into a hot capillary tube. Moreover in 

 case of mercury (table 3) an air bubble discrepancy would 

 necessarily have shown itself at 310°. Errors due to the fact 

 that my curves must be in some small measure isentropic, 

 would induce too slow a volume variation and hence only em- 

 phasize the break. There may be dissociation in some of the 

 above organic substances at this high temperature. Azo- 

 benzol actually decomposes and turns black at 310°. What 

 the effect of dissociation may be in modifying the computed 

 isothermal is not easily conjectured ; for the greater compres- 

 sibility of the dissociated substances is in some degree compen- 

 sated by larger initial volumes. Equation (2), however, must 

 certainly begin to fail. Cf. § 28. 



The high temperature break in question would result in case 

 of inconstancy of temperature in the boiling tube. I did not 

 test the thermal distribution ; the behavior was such throughout 

 that I see no reason to suspect inconsistenc}\ Final reference 

 might be made to the pressure expansion of the capillary tube. 



To throw light on these particulars, I made the following 

 direct measurements with ether, a case in which the high tem- 

 perature break is most pronounced. Table 31 contains an 

 example of the results. The isothermal are referred to unit 

 of volume at 22° and 100 atm. To reduce them to 29° and 

 100 atin., conformably with table 23, the volumes at 310° are 

 to be decreased 1*5 per cent. The length of thread at 22° is 

 only l*85 cm , thus enabling me to observe the whole thread at 

 310°. In other respects the work was done in the manner in- 

 dicated above to make the different data comparable. 



Table 31. 



Isothermals of Ether. Direct measurement. 



#=300°; £ !0 o=6-00 c, » 



p 



Volume. 



Volume. 



P 



Volume. 



Volume. 



P 



Volume. 



Volume. 



atm. 







atm. 







aim. 







100 



3-30 



312 



400 



1-43 



1-41 



700 



1-24 



1-23 



200 



1 83 



1-76 



500 



1-34 



1-32 



800 



119 



119 



300 



1-56 



1-52 



600 



1-28 



1-26 



900 



1-16 



116 



0=22°; Z 100 =l-84 cm 

 100 l'OO 100 300 97 '97 



200 '99 99 400 96 -96 



