GEOPHYSICAL LABORATORY. 



155 



The elements present in large amounts are carbon, hydrogen, sul- 

 phur, nitrogen, and oxygen. The first three occur principally as 

 oxides. The percentage of chlorine is usually very small, and the 

 rare gases are often no more in amount than would be required on the 

 assumption that the nitrogen had come in as air (entrapped in sinking 

 crusts or carried down by f ountaining, for instance) . 



Any extended deductions or speculations as a result of this work 

 may well be postponed until the more recent samples of gas, collected 

 by Dr. Jaggar under conditions selected with reference to particular 

 hues of study of the crater, have been analyzed. This work is now 

 under way in the Laboratory. 



The simultaneous study of these gases from the synthetic side, 

 which has been commented upon in a previous Annual Report,^ 

 has been interrupted by war conditions. A comprehensive discussion 

 of the equilibria and reactions concerned must await further field and 

 laboratory work. 



THE BINARY AND TERNARY SYSTEMS OF SILICA, ALUMINA. MAGNESIA. AND LIME. 



This year sees the completion of the last of the four ternary systems 

 which can be made up from the four oxides, Si02, AI2O3, MgO, and 

 CaO. 



The system Si02-Al203-CaO has been commented on in previous 

 Annual Reports.^ The systems SiOa-AlgOs-MgO and AlaOg-MgO- 

 CaO have been given passing mention in previous reports, while the 

 system Si02-MgO-CaO is new this year.^ A summarized review of 

 some of the salient facts concerning these systems may bring out some 

 points of interest. 



The Compounds. 



The binary and ternary compounds found in these four systems are 

 as follows: 



1 Year Book 15, 141 (1916). See also abstract (7), below. 



» Year Book 7, 97-99 (1908); 9, 91 (1910); 13, 135-137 (1914). 



'See abstracts (4), (23), and (24), below. Also (37), on the forms of silica. 



