GEOPHYSICAL LABORATORY. 159 



To illustrate from the work of the current year: 



Comparatively little work has been done in the investigation of those 

 geophysical problems in which one of the components is volatile, such, 

 for example, as the formation of carbonates, hydrates, sulphates, and 

 the oxides of certain metals. Though the foundations for the 

 theoretical groundwork were laid years ago by Willard Gibbs, the 

 experimental side of the problem has been neglected in the past, chiefly 

 because of the difficulty of attaining equilibrium within the limited 

 time available for a single laboratory experiment and because of the 

 complexity of the systems encountered. 



A recent investigation of the system copper-oxygen, undertaken 

 here, has furnished data for extending the equations of Gibbs to apply 

 to a particular case, has formed a basis for estimating the behavior of 

 other similar systems, and has been the means of developing the 

 necessary technique for the investigation of more complex systems. 



The investigation itself disclosed as solid phases in this system only 

 copper, cuprous oxide, and cupric oxide, all three of which occur as 

 natural minerals, and gave no evidence whatever of solid solution in the 

 system. Measurements were successfully made of pressure and com- 

 position throughout the temperature range between 900° and 1235° C. 

 at oxygen pressures varying from 0.02 millimeter of mercury to 55 

 atmospheres. The data were applied to the calculation of the energy 

 changes involved in the dissociation and to the calculation of the 

 melting-point of cuprous oxide. There is still some work to be done 

 in that part of the system lying between copper and cuprous oxide, 

 but in a field which is of chief importance to the metallurgist. 



Having regard for the potential application of such methods and 

 criteria in the analysis and study of geological problems, it is especially 

 interesting to consider the composition of the igneous rocks as pre- 

 sented in a correlation of chemical analyses by Dr. Washington of this 

 Laboratory in association with Dr. F. W. Clarke of the Geological 

 Survey. For a number of years the effort has been made to apply the 

 data derived from the chemical analysis of igneous rocks to the study 

 of some of the broader aspects of petrology, and more especially of the 

 relation of the elements in igneous rocks and their distribution over the 

 earth. A preliminary statement of some of the results of this study 

 was presented before the Franklin Institute in December 1920, under 

 the title "The chemistry of the earth's crust." Certain particular 

 features of the subject, especially the chemical composition of the 

 average igneous rock of the earth's crust and the relations of the 

 chemical elements in minerals and igneous rocks, are set forth in a 

 forthcoming Professional Paper of the U. S. Geological Survey, after 

 which the general results of the study will appear in book form. 



A new average of the igneous rocks of the earth has been calculated 

 which is based upon 5,159 good analyses of rocks from all parts of the 



