CunnincHam—Crystallization of Minerals in Igneous Rocks. 407 
given for metals, are the graphic representations of their rates of 
consolidation. Their case is simplified by the high conductivity 
of the metals. Von Kobell’s numbers, of course, only pretend 
to be purely empirical, and they may or may not give us an 
idea of the true relative rates of melting. So, in general, they 
cannot be used at present for calculation. But in particular cases 
we may, with a high degree of probability, infer which of two 
minerals has the larger latent heat. Thus, if the above reasoning 
be correct, there can be no doubt that the latent heat of orthoclase 
is distinctly greater than that of labradorite. Similarly augite 
Melting Temperature 
o 
is) 
(e) 
ie 
fo) 
2 
7 Atm. 
Pressure 
Fic. 9.—Diagram showing the Variation with Pressure of the Melting Points of 
Quartz, Orthoclase, and Augite. 
and hornblende are more easily fusible, but have higher melting 
points than orthoclase, and, therefore, their latent heats are 
smaller. At the same time the volume-change of augite, as here 
deduced from its loss of density on fusion, is distinctly greater 
than that of orthoclase. There can then be no doubt that the 
5p 
1G 
That is, the rate of increase of melting-point with increase of 
value of the ratio ~~" is greater for augite than for orthoclase. 
GONE ae. : 
_ pressure 2 is evidently greater for augite than for orthoclase 
(fig. 9). If this relative position of these two minerals may be 
