THE ISOMORPHISM AND THERMAL PROPERTIES 



OF THE FELDSPARS.* 



The investigation here recorded is the first chapter in a rather com- 

 prehensive plan for the study of the rock-forming minerals at the 

 higher temperatures. In its broader outlines, at least, it is by no 

 means a new plan. Mr. Clarence King and Dr. George F. Becker 

 were inspired by a desire to reach the mineral relations from the ex- 

 perimental side, which is recorded in the very earliest records of the 

 U. S. Geological Survey, and much of the remarkable ground-breaking 

 work of Prof. Carl Barus was undertaken in furtherance of a carefully 

 prepared scheme of research along these lines. The matter has been 

 advanced but little in the intervening years. The present renewal 

 of the effort in this direction is again due to Dr. Becker and has had 

 the benefit of his wide field experience and enthusiastic and effective 

 cooperation throughout. 



In October, 1900, one of the authors was called from the Reichsan- 

 stalt to equip a laboratory in the U. S. Geological Survey in which the 

 exact methods and measurements of modern physics and physical 

 chemistry should be applied to the minerals. The ultimate purpose 

 was geological, to furnish a better basis of fact for the discussion of the 

 larger problems of geology, but it appeared highly probable also that 

 a quantitative study of the thermal phenomena in this class of sub- 

 stances would offer new relations of intrinsic interest and of consider- 

 able theoretical value. This inference has been happily substantiated 

 quite recently through the publication by Tammann of an extended 

 treatise on melting and crystallization,! in which he offers some very 

 interesting speculations on the conditions of equilibrium for sub- 

 stances above and below the melting temperature under different 

 pressures. The behavior of crystalline minerals which melt at tem- 

 peratures considerably higher than he was able to command offer 

 peculiarly advantageous opportunities for verifying the truth of his 

 inferences and of contributing further to the knowledge of this most 

 important change of state of matter. 



* A preliminary paper containing the chief results of this investigation was 

 read before the Geological Society of Washington, March 25, 1904, and a brief 

 abstract published in Science (vol. xix, p. 734), May 6, 1904. A second abstract 

 appeared in the American Journal of Science (4), 19, p. 93, 1905. 



f Tammann, " Krystallisiren and Schmelzen." Leipzig, 1903. 



*5 



