258 day: geophysical research 



of great individual skill in these industries are much less neces- 

 sary now than formerly. Everything is accomplished by bring- 

 ing temperature conditions under mechanical control and mak- 

 ing them absolutely reproducible without the exercise of critical 

 judgment on the part of anyone. 



A more intimate knowledge of the behavior of the minerals 

 themselves finds almost immediate industrial application. An 

 industry which has grown to enormous proportions in recent 

 years is the manufacture of portland cement, about which little 

 more has been known than that if certain natural minerals were 

 taken in the proper proportions and heated in a peculiar furnace 

 developed by experience, the resulting product could be mixed 

 with water to form an artificial stone which has found extensive 

 application in the building trades. Chemical analysis readily 

 established the fact that the chief ingredients in a successful 

 portland cement were lime, alumina and silica, with a small admix- 

 ture, perhaps, of iron and magnesia; but the relation in which 

 these ingredients stood one to another, — that is, which of them 

 were necessary and which merely incidental, — and in what 

 compounds and what proportions the necessary ingredients 

 required to be present, has never been satisfactorly established. 

 When we know the stable compounds which lime, alumina and 

 silica can combine to form, together with the conditions of equi- 

 librium between these for different temperatures and percentages 

 of each component, a formula can be written offhand for a success- 

 ful portland cement from given ingredients somewhat as an experi- 

 enced cook might write out the recipe for a successful dish. Such 

 definite and valuable knowledge is not beyond our reach. To 

 obtain it requires, in fact, precisely the same system of procedure 

 which has been described above and which has already been suc- 

 cessfully applied to many of the natural minerals which have been 

 reproduced and studied in the Geophysical Laboratory during 

 the past five years. It happens that we have examined a con- 

 siderable number of these very mixtures in our recent work upon 

 the rocks. All the compounds of lime, silica and alumina have 

 been established, and a portion of the silica-magnesia series, and 

 their relations have been definitely determined thruout the 



