.132 Mixtures with Maximum or Minimum Vapour-Pressure. 

 gives x 1 grammes of gaseous ethane : this quantity requires 

 — (1 — #2) grammes of carbon dioxide, so that 



x 1 , N $2 ~~ x i 



i_^ 1 _^ (1 _., 2)= _ r 



grammes will be solidified. We thus find for the heat 

 absorbed, and the corresponding increase of volume near T, 



H = Jj lv — l - A — Ji l ^ •= - 1 L sr — L „ + ^m • • • ( 2 ) 



il/2 *"2 



V as V v — VI — ^ 3 '' l (V v - Vs) = — (V v — V 8 ) —V t + V s . (3) 

 i#2 <^ > 2 



At T itself we must take for L st > the heat of sublimation, and 

 for ~L lo the heat of evaporation of carbon dioxide, and 



the sign of H thus depends upon whether - I Jy-^ The 



value of this fraction for carbon dioxide is 43*8/129 , 9 = *34. 



The amount of ethane in the vapour is thus found to be more 



dr) 

 than three times the amount in the liquid. The value of -vjr 



at T is about — '10 atmosphere per degree. By means of 

 the expression for H (1) combined with ^2) and (3) we can 

 now calculate both x Y \x 2 and H. The result is x l /x 2 ='26, 

 and H= — 9*9 calories. 



If we apply the above formula (2) for H to the condition 

 at where fi = 0, we can obtain an approximate value for 

 the ratio Xi/x 2 at that point. Taking for L sv 129 calories, 

 and hi v 88 calories, we find x 1 /x 2 ='32. According to this 

 calculation, which however is only very approximate, the 

 ratio of the compositions of the liquid and vapour, which 

 according to Henry's law would be a constant within certain 

 limits, has only come up from *26 at T to *32 at 0. At M, 

 as we saw before, its value reaches unity. 



The direction of the three-phase curve at T agrees with that 

 found by Stortenbeker* for mixtures of iodine and chlorine. 

 Bakhuis Roozeboom and van der Waalsf were the first to 

 discuss the properties of such curves from a general thermo- 

 dynamical point of view. We hope that the above Avill be 

 found to contain a not unimportant addition to our knowledge 

 of the subject. 



University College, 

 Dundee. 



* Stortenbeker, Zeit. phys. Chem. iii. p. 19. 

 t Roozeboom, Zeit. phys. Chem. ii. p. 462. 



