486 Dr. Meyer Wilderman on the Velocity of 



For the velocity of reaction we have : — 



For BaS0 4 solid*or««-BaS0 4 in sol. :— 

 f dt' 



[j t ) = c ^t{Po-Pt). 



For K 2 C0 3 in sol. + BaSo 4 in sol.*-BaC0 3 in sol. + K 2 S0 4 



[in sol. : — 



\-J-) =Cp T .pr — <f'p T m • Pt 1y . 



For BaCO.Q solid->or<-BaCO= in sol.: — 



( 



fX=0"^r'( P :- P r"'). 



Now in a unit of time just as many molecules of solid BaC0 3 

 or of K 2 S0 4 in solution are formed as molecules of BaS0 4 

 have disappeared. Consequently 



\dr)~\dT) \dr)' 

 From ( -7- ) and l-r) the value of p T can be eliminated and 



/ -y-\ can be represented as a function of Sr, Pr\ Pr" 3 Pr ix ; 

 i. <?., from this equation and ( j-J we can further eliminate p r '" 



and so ultimately get (-7-) as a function of 2r, 2r', p T ', pr lr , 



i. <?., as a function of values which can all be directly observed 

 and can be conveniently verified experimentally. Thus we 

 see that in every system we have always n + 1 equations if 

 there are n terms, of which each is common to two equations, 

 i. e., we are always able to eliminate these terms, very often 

 inaccessible for quantitative measurements. 



It is evident that the laws of chemical velocity of reaction 

 in heterogeneous systems can be best verified experimentally 

 in cases where the vapour-pressure or the solution -pressure 

 of the solid (or liquid) is not too small ; then every one of 

 the equations 



©. m- ©r*- 



can be directly investigated and the velocity constants de- 

 termined. 



