8 Strom F,\'I-:r, TJie Forviation of Minerals in Granite, 



the felspars were to rise, it would be evident that at a 

 depth of 200,000 feet we mii^ht expect q lartz to melt 

 at about i, 000 ''C, and felspar to melt as above at i,900°C. 

 If this could be demonstrated, the origin of almost any 

 granite could easily be explained. That such values are 

 not impossible will be seen from Table IV., which contains 

 the elements for calculating the changes of melting 

 temperatures of various substances, when the pressure is 

 increased. The estimated rates are given in the seventh 

 column and two experimental results are given at the 

 foot. For some materials no estimates could be made, 

 owing to want of complete information. Antimony and 

 arsenic are well-known cases of contraction on fusion, but 

 its amount and other necessary elements are not known. 

 The table contains such information as could be collected 

 on this subject, except as regards organic compounds, 

 and, although it throws no direct light on the important 

 question of the melting temperatures of minerals when 

 under great pressure, it shows at least that amongst eleven 

 substances, of which only two are compounds, the rate of 

 change may var}- from — 0'0073 for ice to +0"Oo66 for 

 sulphur, and it is not unreasonable to suppose that similar, 

 if not greater, differences of rates will be met with amongst 

 minerals. 



The formula for calculating -^ the rise of melting 



^ dp ** 



temperature with the pressure is 



dt , V,- K 



Avhere /= (absolute) melting temperature, 



y= Joule's mechanical ec|uivalent of heat = 42,658 g.c, 

 A = latent heat of melting, 



Vy and F, = volume in cub. cm. of i gram of substance 

 in the fluid and solid states respectively 

 at the melting temperature, and 



