Thermal Properties of Normal Pentane. 

 Isochors read from Isothermals. 



361 



Volume. 



90. 



100. 



120. 



140. 



160. 



180. 



200. 



230. 



260. 



300. 



350. 



Temp. 











Pressure. 













o . 



1 40 





















857 





i 60 













1485 



1347 



1182 



1053 



920 





80 





2705 



2304 



2001 



1773 



1589 



1440 



1260 



1123 



981 





100 



3187 



2907 



2464 



2137 



1889 



1693 



1532 



1340 



1193 



1040 



896 



120 



3404 



3098 



2620 



2272 



2005 



1794 



1622 



1419 



1262 



1100 



947 



140 



3613 



3285 





















160 



3832 



3477 



2931 



2534 



2233 



1996 



1804 



1576 



1400 



1219 



1048 



200 



4237 



3832 



3231 



2791 



2458 



2196 



1981 



1729 



1535 



1334 



1146 



240 



4653 



4212 



3536 



3047 



2679 



2393 



2i57 



1882 



1669 



1451 



1246 



280 



5087 



4588 



3836 



3305 



2905 



2592 



2337 



2038 



1808 



1571 



1349 



The values of b and a in the equation p = bT — a were 

 obtained graphically from the preceding data. As with iso- 

 pentane, the deviations are exceedingly small at the largest 

 and smallest volumes and about the critical volume, but are 

 larger at intermediate volumes ; they exhibit a similar regu- 

 larity and are in the same direction as with isopentane. Here 

 again the relation p = bT — a at constant volume, if not abso- 

 lutely true, may be taken as a very close approximation to the 

 truth. 



In studying the variation of b and a with the volume it 



w r as found convenient, in the case of isopentane, to plot the 



. , 10,000 . e 10 10 . , i , ... , . . 

 values or — ] and or — T against v 3 : and this has also been 



V ^r, _! 10* 



done for normal pentane. The values of b } a, v 3 ; -y— , and 



10 10 . 



for a series of volumes are given in the table below and, 



10* 



av 



for the sake of comparison, the corresponding values of 



10 io bv 



— - for isopentane are added 



values of 10 10 /av 2 



(Table p. 362.) 

 plotted against v 



in the 



and 



av" 



The values ol . 

 diagram on p. 363. 



In a former paper by one of the authors (Phil. Mao-, xliv. 

 p. 77) it was pointed out that, besides the quantities b and a, 

 it is often useful to consider a fresh quantity r, which is 

 defined as follows : — For each volume there is one and onlv 

 one temperature at which the gas has its pressure equal 

 to that given by the laws of a perfect gas : this temperature 

 is denoted by t. It is also shown that the numerical value 



