1147 



Write then for the second term of (45): h ^-Q . (hv'\ wherein Q is 

 positive. From (6) it follows that we may write Vx and H^ for the 

 coefficient of (IF and ^/7'; (45) passes into: 



F, . dP—Hx .dT=\.*^.Q.d.e (46) 



From (44) and (46) follows: 



'Lx[Ha{V:-,:')-V,{H,-iiJ]dP= - ciH-rDQdx-^ . (47) 

 2,x \Hx{V,-v')- Fx- (//—>/)] dT = - ciV,-ü') Qd.e . (48) 



As V,—v'= V\,:r and H, -i]' — Hu, we see from (24) that the 

 coefficients of dP and c/7' in (47) and (48) are positive. Therefore, 

 dP and dT are zero at tirst approximation, at second approximation 

 negative so that pressure and temperature are maximum. 



We may summarise the previous results in the following way: in 

 a P,T-diagram tiie sublimationcurve of the Ice and the cryohydric 

 curve under its own vapourpressure [P^ -[- ice -\- L -\- G) coincide. 

 The cryohydric curve under a constant pressure has its maximum- 

 temperature in the pure solutionpoint of F; the cryohydric curve 

 under its own vapourpressure has in this point its maximumtempe- 

 rature and -pressure. 



When i^ is a binary compound, we must in the previous consi- 

 derations not only put a' = 0, /5' = 0, :i\ = and y^ = 0, but 

 also a=0. From this follows: F = — [Iv, F^ = 0, Fi, = V,-~v' 

 and H{,x^=ffi — v'- From (10) again it follows that: 



dP H,—ii' 



— z=^ — - (49) 



dT V^-v' ^ ^ 



so that in a 7^, 7^-diagram again the sublimationcurve of the ice and 

 the cryohydric curve F -\- Tee -\- L -\- G coincide. 



Considering the cryohydric curve in the vicinity of the binary 

 cryohydric point F -\- ice -\- L^ -{- Gq, it follows from (25) and (26): 



dP RT RT RT 



dx K K K 



dT RT"" RT^ 



dx K K 



From the binary cryohydric point, therefore, pressure and tempe- 

 rature decrease along the cryohydric curve. 



We can also obtain these results by substituting Z ^= U -\- RT x 

 log X in the three equations (41). 



Now we shall suppose that F and F' are modifications of a same 

 substance, so that F -\- F' -{- L -{- G represents the moditicationcurve 



