24 



Day, etc. — Determination of Mineral 



which he used, on the basis of a specific gravity of 2'627 at 

 room temperature.* The results are plotted in fig. 8. 



These expansion measurements by Wheeler were made on a 

 20-centimeter bar of rock the ends of which were viewed 

 through side openings in the furnace tube. This method 

 would tend to cover up any irregularities in the expansion, 

 since the portion near the ends of a heated bar may lag in 

 temperature considerably behind the remainder of the speci- 

 men, even under conditions of stationary temperature. We 



Fig. 8. 







SPEC 









3URV 



















GRANITE 























































- *=*^=^= 

























___^^ 

































































TEMPERATURE 



have found this to be true in a similar apparatus in which 

 measurements were made on platinum alloys, f On account 

 of this temperature gradient, the effect of a transformation 

 which is complete at a definite temperature may be spread 

 over a considerable range of temperature. The break in curva- 

 ture near 575° is therefore much less marked than in our own 

 curves. It is noticeable, however, especially on Wheeler's cool- 

 ing and reheating curves for the same block. 



Under the conditions above noted, there would have been no 

 purpose in carrying on the experiments to a temperature suf- 

 ficient to liquefy the granite, since the true dilatation of the 

 crystalline rock can not be determined. Under the heavy 

 pressure of overlying rocks the dilatation due to fracturing and 

 differential expansion would be less than that obtained in ex- 



* Datum from F. D. Adams, private letter, 1913. 



f Day and Sosman, this Journal (4), xxvi, 425-441. 1908 ; xxix, 114, 1910 ; 

 Carnegie Inst. Publ. 157, pp. 35, 63. 



