PRESSURE IN FORMATION OF ROCKS AND MINERALS 735 



occurs for it to do so, since the stresses to which it is exposed must 

 be far in excess of its elastic Hmit, even at moderate depths. 



TABLE I 

 Melting-Curves of Various Substances (after Bridgman) 



Pressure 

 Kg. Per 

 Sq. Cm * 



Mercury 



Potassium 



Sodium 



NiTROBENZOL 



Carbon 

 Dioxide 



P 



t 



At 



t 



At 



t 



At 



t 



At 



t 



. At 



I 



-38.85 





62.5 





97-6 





5-6 





-56.6 









5-10 





16.2 





8.6 





21. g 







193 



1,000 



-33-75 



5-09 



78.7 



13-7 



106. 2 



8.1 



27-5 



21.2 



-37 



3 



16.8 



2,000 



-28.66 



5-09 



92.4 



12.3 



II4-3 



7.6 



48.7 



19.9 



-20 



5 



15-2 



3,000 



-23-57 



5-09 



104.7 



II. I 



121. 9 



7.2 



68.6 



18.8 



- 5 



3 



13-8 



4,000 



-18.48 



5.08 



IIS -8 



10.2 



129. 1 



6.9 



87.4 



17.7 



+ 8 



5 



12.7 



5,000 



-13.40 



5.08 



126.0 



9-4 



136.0 



6.6 



105. 1 



16.9 



21 



2 



II. 7 



6,000 



- 8.32 



5-07 



135-4 



8.7 



142.6 



6.3 



122.0 



16. 1 



32 



9 



II. I 



7,000 



-3-25 



5.06 



144. 1 



8.1 



148.9 



6.1 



138. 1 



15-5 



44 







10.6 



8,000 



+ 1. 81 



5.06 



152.2 



7-5 



155-0 



5-9 



153-6 



151 



54 



6 



10.2 



9,000 



6.87 



5-05 



159-7 



7.0 



160.9 



5-7 



168.7 



14.8 



64 



8 



9-9 



10,000 



11.92 



5 -04 



166.7 



6.6 



166.6 



5-4 



183 -5 



14-5 



74 



7 



9.6 



11,000 



16.96 



5-03 



173-3 



6.2 



172.0 



5-2 



198.0 





84 



3 



9-3 



12,000 



21.99 





179-5 





177.2 









93 



6 





■I atm. = 1 .033 kg. per sq. cm. 



As regards the magnitude of the effect of uniform pressure in 

 raising the melting-point of a pure silicate, there are no experi- 

 mental data; but the initial slope of the melting-curve could be 

 calculated if the latent heat and volume change on melting were 

 known. The relevant evidence is very scanty and unsatisfactory; 

 but, so far as it goes, it indicates that the latent heat is of the order 

 of 100 cal.^ per gram and that the volume change ranges up to 10 



^ With regard to this estimate see: J. H. L. Vogt, Die Silikatschmelzldsungen, II 

 (1904), 65; W. P. White, Am. Jour. Sci., XXVIII (1909), 486 (footnote); G. Mulert, 

 Z. anorg. Chem., LXXV (1912), 238. 



