136 CARNEGIE INSTITUTION OF WASHINGTON. 



the simplest parts of the system and the different thermal and optical 

 methods essential for such work were devised, tested, and improved 

 as the work progressed. As a result, a large part of the time expended 

 has been required for the development of methods which are now per- 

 fected and have been found satisfactory and easy of general apphcation. 



In the study of the lime-alumina-silica system, fully 1,000 different 

 mineral preparations have been made up and over 7,000 heat treat- 

 ments and microscopical examinations undertaken upon them. These 

 preparations and the results obtained with them are filed and are 

 available for future reference. A brief statement of the data obtained 

 and also of the physico-chemical interpretation of these data is given 

 in the paper by Rankin and Wright, of which a brief review will be 

 found on page 155. The problem will be treated in greater detail and 

 the methods which are of general interest and importance will be de- 

 scribed in a later monograph. 



Incidentally, it is interesting to note that in the ceramic, glass- 

 making, and allied industries these methods of combined physico- 

 chemical and microscopical research are attracting inquiry and are 

 being gradually adopted. In particular, the petrographic microscope 

 has proved to be a most efficient and simple tool in the service of such 

 industrial research and its use is certain to become increasingly im- 

 portant as this fact is realized by the technical world. 



In the annual report for 1912 (Year Book No. 11, page 98) the 

 purpose of these studies of lime, alumina, and silica was stated to be to 

 ascertain: 



(1) All the compounds of these three ingredients which are possible. 



(2) The temperatures within which each of these compounds is stable and 



therefore capable of independent existence. 



(3) The relation between each compound and any or ail of the others at 



whatever temperature. 



(4) The behavior of these individual compounds or groups of them in the 



presence of water at various temperatures. 



(5) The application of this information to the study of natural rocks or 



to the making of artificial rocks (cements). 



Of these studies the first three, which bear directly upon our problem 

 of rock formation, are completed and in press. The fourth applies 

 more specifically to hydraulic cements and hardly enters into the prob- 

 lem of igneous-rock formation. Accordingly, although we had already 

 done some work upon this phase of the investigation also, it was prac- 

 tically discontinued as soon as we learned that a much more appro- 

 priate institution, the Bureau of Standards, had made provision for 

 extensive studies in the same field. There appeared to be no reason 

 for a duplication of activities which were leading in a direction some- 

 what apart from our primary purpose. 



The applications (paragraph 5) of the methods and data which 

 have been gathered in these studies have proved to be manifold and 



