378 EEPOET— 1886. 



§ 14. Action between liquids and solids. 



[The author claims even for solids a certain electrolytic conductivity, and hence 

 a certain, though very small, coefficient of activity. It is thus necessary for 

 completeness to consider the action between liquids and insoluble solids. But 

 inasmuch as the activity of even a trace in solution is much greater, because spread 

 all through a liquid, than the action of a limited area of surface can be, he says the 

 latter may be safely neglected, and states the law] — 



(48) If a system is heterogeneous with respect 1o a solid body, of tohich, never- 

 theless, a very small part is dissolved in the surrounding liquid, one 

 can neglect the reactions which occur at the surfaces of contact between 

 liquid and solid. 



§ 15. Velocity of the reactions. 



[In accordance with a previous section the velocity with which Ij Jj and I^ Jj 

 are formed (or with which Ij 3^ and I^ Ji are destroyed), i.e., the velocity of 

 the reaction, is — 



K (g' /3 . py — ma . n8). 



The author applies this to etherifications, where the water, alcohol, and ether have 

 insignificant coefficients, the acid being the only active body. In this case the 

 velocity is proportional to ^y, and so simply to the activity of the acid used, being 

 quicker with nitric than with acetic] 



§ 16. Calculation of numerical examples. 



The coefficients of activity being not quite constant, according to the first part^ 

 slightly different numbers must be used for higher concentrations. 



§ 1 7, Conservation of the type, and predisposing affinities. 



[Remarks on reactions among non-electrolytes, and on the behaviour of KjFeCy^ 

 with reference to Berthelot's hypotheses on ' conservation of type ' and ' predis- 

 posing affinities.'] 



§ 18. Molten electroljrtes 



should behave just like others. 



§ 19. Cases to which Berthollet's laws are not applicable. 



M. Berthelot cites some of these cases. They can be put under two general 

 heads. Either a feeble hydrate is unable to displace a stronger hydrate, although 

 one of the products of displacement is but slightly soluble, or a volatile acid 

 (HCl and HNO3) partially displaces another acid (H^SO^), although this acid is 

 not volatile. 



The first case is represented by the formula — 



{l-xy'a8 = a;»/3y < e«/3y,^ 



where the feeble hydrate and the salt of the strong hydrate are present in equiva- 

 lent quautities (originally 1), and where c is the soluble quantity of the sUghtly 

 soluble substance, x is the quantity of this substance formed, but as x is less than 

 c none is precipitated. 



One may write the inequality, a foi-tiori, — 



(l-c)2a5< c^iSy, 

 or — 



c lab, 



l-c^VWy' 

 so if this inequality is satisfied there is no precipitate, a belongs to the feeble 

 hydrate, /3 to the strong, 5 to the salt of the latter, y to the salt of the former 

 (the slightly soluble substance). aS//3y is in general pretty small, so c may be 

 very small and yet no precipitation occur. 



