THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. VII. — The Isomorphism and Thermal Properties of 

 the Feldspars ; by Arthur L. Day and E. T. Allen. 

 (With Plate I.) 



The investigation here recorded is the first chapter in a 

 rather comprehensive 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 experimental side, which is 

 recorded in the very earliest records of the IT. S. Geological 

 Survey, and much of the remarkable ground-breaking work of 

 Professor Carl Barus was undertaken in furtherance of a care- 

 fully 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 the benefit of his wide field experience 

 and enthusiastic and effective cooperation throughout. 



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

 Reichsanstalt to equip a laboratory in the IT. S. Geological Sur- 

 vey 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 quantita- 

 tive study of the thermal phenomena in this class of substances 

 would offer new relations of intrinsic interest and of considera- 

 ble theoretical value. This inference has been happily sub- 

 stantiated quite recently through the publication by Tammann 

 of an extended treatise on melting and crystallization,* in which 



* Tammann, " Krystallisiren nnd Schmelzen." Leipzig, 1903. 



Aii. Jour. Scl— Fourth Serees, Yol. XEX, No. 110. — February, 1905. 

 7 



