164 



CiiO at V (iemand that tlie SO, -press ure of V is equal to that ot VII 

 so that jPso, = ,Psoz- 



These relations substituted in [n) give : 



rP-SO, • 7/'0.> =-Ps''-- 6P5«, (f>) 



In this j/^502 '^'id .po» '"^.V t»e calculated from the ol)servations 

 of the total pressure P, if tlie dissociation degree « of the SO, is 

 known. Then we have : 



and hence, substituted 



2 -|- a K 2,-\-a 



or : 



PJI, 2« ./— \ 



'^^""^ P^k (2+«)' • •■•(«) 



and ( 



•f 6 = ^8 + 6P50, + 7P50, ) 



In this last equation ^pso^i will be very great in proportion to the 

 two other terms ; at the first approximation the total pressure of 

 reaction V might be put equal to ^pso^i- 



15. From the foregoing it appears that it is possible to calculate 

 the equilibrium pressure of V if we know : 



a. the dissociation pressure at the equilibrium VII ; 



h. the dissociation degree of the SOj at the pressures of VII ; 



c. the dissociation pressure of CuO. 



The first quantity is known from our determinations given in table 

 VII. The second can be calculated accurately from the careful 

 investigations of Bodenstein and Pohl '). We have done this for 

 various temperatures and pressures which are interpolated graphi- 

 cally from our measurements of VII (see column 5 of table VIII). 



The dissociation pressure of CuO into Cu,0 and 0, is extrapolated 



from the observations of Wohler ') with the aid of the formula 



1/1000 

 /o.aP,= 13,077 -— , 



which agrees excellently with his observations. 



With the aid of formula (c) the equilibria pressures P^ have been 



1) Zeitschr. f. Elektroch. 11, 373 (1905). 

 "-) Zeitschr. f. Elektroch. 12, 704 ii906). 



