BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 21, pp. 141-178, PL. 3 May 26, i9io 



SOME MIXEEAL EELATIOXS FKOM THE LABORATORY 



VIEWPOINT^ 



BY ARTHUR L. DAY 



{Presented in abstract before the Society December 30, 1909) 



- CONTENTS 



Page 

 Purpose 141 



Some reasons for accurate laboratory work 143 



Temperature measurements are now trustwortliy and of adequate rani;e. . 144 



Interpretation of melting-point data 14.") 



Individuality of different minerals in melting 146 



Uncertainty of solidification — undercooling 148 



Some difficulties of interpretation where glass is present 149 



Their effect upon the early measurements 150 



Can trustworthy melting temperatures be obtained? 151 



Other minerals lower the melting temperature 152 



Pure tj^pes are necessary 153 



Preparation of pure minerals 154 



All governing conditions must be known 155 



Melting "points" and melting intervals 15G 



Significance of "equilibrium" 161 



Effect of pressure 161 



Single minerals — summary 162 



Mixtures of minerals 163 



The eutectic relation 164 



The isomorphous relation 166 



Si^nple mixtures — summary 168 



Molecular composition at the moment of crystallization 168 



Chai'kcteristics of the cooled products — some definitions 169 



EutectLcs in complicated mixtures 171 



Km illustration of a cooling mixture. 171 



Incomplete reactions I74 



The application of Van't Hoff's law — Vogt I75 



Summary and conclusion — the geologic thermometer 176 



Purpose 



Rocks have come to their present condition as the result of profound 

 changes in physical structure and in the physical and chemical relations 



1 Manuscript received by ttie Secretai-y of the Society April 11, 1910. 



XI — Bull. Geol. Soc. Am.. Vol. 21. 1000 (141) 



