218 Johnston and Adams — High Pressures on the 



Correlation of Mechanical Properties of Metals with the 



(Unequal) Pkessure Required to Depress their 



Melting Points to Ordinary Temperature. 



Further corroboration of the plausibility of the view that 

 unequal pressure is effective in correlating phenomena attend- 

 ing the deformation of crystalline solids is afforded by a con- 

 sideration of the parallelism observed between the calculated 

 melting pressures ($) at ordinary temperature and certain of 

 the mechanical properties of metals. 



The (unequal) pressure (<£, expressed in atmospheres) 

 required to cause a substance to melt at the temperature T^ 

 can be computed if we can integrate equation III. We cannot 

 perform this integration rigidly for lack of the necessary data 

 on the variation of AH and V s with pressure and tempera- 

 ture; but fortunately the variation of T^/AH is small and for 

 the present purpose unimportant. We may therefore con- 

 sider VJAF1 to be independent of pressure and temperature : 

 by integration and transformation we then obtain the equation 



<£ = 95-1 QD log |f (V) 



2 



which gives the melting pressure (<£) at the temperature T 2 in 

 terms of the heat of melting ((>, in calories per gram) the 

 density D and the ordinary melting point at one atm. pressure 

 {T 1 in absolute measure). 



At the present time the requisite data for the calculation of 

 <j> are available only for a few metals ; these calculations have 

 been made, and the results are presented in Table II. This 

 and the following table are taken from another paper,* in 

 which the results are discussed at some length. We shall 

 therefore recapitulate the discussion only in so far as it is 

 germane to the present subject. 



The sequence of the metals when arranged in the order of 

 their $ values (as calculated by equation V) is identical with 

 that obtained when they are arranged in the order (1) of their 

 flow pressuresf (2) of the following mechanical properties^:; 



* Johnston, J. Am. Chem. Soc, xxxiv, 788-802, 1912; Zs. anorg. Chem., 

 xxvi, 361-79, 1912. A preliminary note embodying the main conclusions 

 appeared in J. Washington Acad. Sci., i, 250, 1911. 



f As observed both by Tammann, Verigin and Levkojeff (Ann. Phys., x, 

 649, 1903; and by Kurnakov and Zhemzhazhny (Zs. anorg. Chem., lxiv, 174, 

 1909). The amount of compression required to cause a material to flow is 

 characteristic of the material under specified conditions ; but at constant 

 temperature it varies, as is obvious, with the size of the aperture through 

 which the flow takes place ; probably also it depends upon the shape of the 

 aperture and upon other subsidiary factors. Hence determinations of flow 

 pressures are not comparable, except they have all been made in the same 

 apparatus and in the same way. This condition is fulfilled by the experi- 

 mental observations cited, which lead to reliable relative values of the flow 

 pressure for a series of metals. 



\ The values of these were collated and averaged largely from the Landolt 

 Bornstein-Meyerhoffer Tabellen (2 Aufl. 1905). 



