78 Mr. J. Kam on Molecular Attraction and 



For Carbonic Acid, Andrews found 

 v c = -0066, 

 p c = 77 atmospheres (experimental value). 



We have (equation 17) 



c = ±v c = '0033 ; 

 hence, according to equation (19), we calculate 

 c -0033 „ a , , 



For Methyl Acetate we have 

 v c = '0096, 

 p c = 47 '54 (exp. value) ; 



1161106 C - 0048 '9AU 1 1 ^ 



Pc = v~? ^ 7 009b r2 = ° ° 8 (ca C * Value) - 

 For Propyl Alcohol, 



v c = -0098, 



p c = 50-16 (exp. value) ; 

 hence -0049 



p c = .aaqq2 = 51 '65 (calc. value) ; 



and so on. All substances following the rule 2.p c .v c = 1 

 must naturally comply. In case of dissociation or con- 

 densation during the experiment, large deviations may be 

 expected. Thus acetic acid and compounds of [OH] gene- 

 rally show deviations beyond the somewhat large errors of 

 observation. 



Equations (D) and (E) hold good for any temperature 

 between T c and 273. They are, in fact, quadratic equations 

 with the three variables p, v, and T. For every value of p 

 and T we have two values of v satisfying the equation, the 

 one being the volume of the saturated vapour, the other 

 the volume of the liquid of the vapour the moment it 

 has entirely disappeared. The curves of these equations 

 consist of the points in which the equal-pressure lines 

 cut the isothermals, and denote the two extreme values 

 of v. Each point of these curves is a point of intersection 

 of the quadratic curve, an equal-pressure line, and an 

 isothermal. At the vertex of the quadratic curve the two 

 points indicating the two values of v coincide with the three 

 points of the critical isothermal denoting the three values 



