Minerals of the Composition MgSiO % 



421 



made evident to the eye by continuing as a dotted line the 

 course the curve would have followed/ had no absorption of 

 heat occurred. 



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Time— 1 interval = 10 minutes. 

 Fig. 13. Curves showing heat absorption in melting orthoclase. 



Figures 14-18 (Tables X-XIV), show the curves obtained by 

 the new method on the different forms of magnesium metasili- 

 cate. The curves for the orthorhombic amphibole, enstatite 

 and monoclinic pyroxene in fig. 14 (Table X) were obtained 

 in preliminary experiments, and are less accurate than those 

 obtained in the later experiments, due to the fact that the posi- 



