THE HEAT OF RKL.VXATIO.V OF THK LEAD LATTICE 



121 



by VAN Liempt's method. Tlio s 'irdilfiision (s:-lf-ivaction) in lead accord- 

 ingly represents, at least formally, an example of a chain reaction in 

 which the chain length is independent of whether single crystals oi' 

 polyerystalline materials ar(> involved. 



The magnitude of the heat of relaxation is compared, in Tal)le 4. with 

 the energ}^ content and the heats of fusion and vaporization. 



T.\i!LK 4. — TTk.\t Pk()Pp:kties of Le.\d 



kc:il/K iitoni 



Heat of fusion 



Energy content at the melting point 



Heat of relaxation 



Heat of vaporization 



1.1 

 3.5 



27.9 

 36.2 



Table 4 shows clearly that the heat of relaxation is not very mudt 

 less than the heat of vaporization but that it is very much greater than 

 the energy content at the melting point and the heat of fusion. 



Suinniary 



The heat of relaxation of the lead lattice (heat of activation for the self-reaction 

 of the lead atoms) amounts to 27,830 cal/mole. This quantity, like the constant 

 A of the diffusion equation, is only slightly stiuctuie sensitive. 



