TQOS'] 



Mills — Molecular Attraction. 



93 



formula or those obtained from equation 4 are correct. The 



8P 

 result is shown below, the value of the y~- at the exact crit- 

 ical volume having- been obtained from the above mentioned 

 capers by interpolation and entered in the column marked 

 'Observed". 



Substance 



jjther 



isopentane 

 formal pentane 



Volume 



3.815 

 4.268 

 3.305 



From Biot 



391.6 

 367.8 

 364.8 



Equ'tion 4 



441.9 

 405.7 

 402.3 



Observed 



401 



436 



to 411 



406.7 



In every case the values accord to within the limit of 

 •xperimental error with the values derived from Biot's equa- 

 ion. (It is not possible to extend the comparison to the alco- 

 iols and acetic acid studied by the observers above mentioned, 

 jor these liquids are associated and equation 4 depending- on 

 he molecular weight, could not give correct results. 



on biot's formula for vapor pressure. 



i 



It seemed to us reasonable to conclude from the above com- 



8 P 

 arison that the ratios of the y=- calculated from equation 



at the critical temperature and shown in Table 1 were the 

 orrect values and that the values obtained from Biot's 

 Drmula were in error. Fortunately we had a means of ven- 

 ding this conclusion directly. 



8P 

 If the vapor pressure curve be plotted, the -^j= is the tan- 



ent to the curve. Assuming that Biot's formula does cor- 



^ctly represent the vapor pressures until the critical temper- 



ture is approached (an assumption justified by a very careful 



xamination of the curves over the entire range of tempera- 



8 P 

 ire) it is evident that if the -«7p- calculated from Biot's form- 



