and Laboratory Methods. 1591 



The different salts of mica variety readily form isomorphic mixtures with 

 each other, and also with metasilicates, etc. 



All " derivatives " can be synthetically obtained at definite temperatures by 

 bringing together the mica nucleus silicate and the material to be added, and 

 may be represented by the general formula ;«R2Al2Si2+n02n 4 • ■^- The sub- 

 stance A may be replaced by another Aj etc., without alteration of the nucleus. 



The physical characters of " derivatives " are peculiar. For instance, the 

 derivatives of many colorless alumosilicates are strongly colored ; for instance : 

 /. Na2Al2Si208 • A, rose and red cancrinite, yellow cancrinite, blue lapis 

 lazuli, haiiynite, sodalite. 



The important groups are : mica group, leucite group, feldspar group, 

 nephelite group, epidote group, garnet group, under each of which structure 

 formulae are given. 



The Clays. — The Clays, under this theory of the silicates, are free acids. 

 No clay corresponding to the chlorite nucleus has been found in nature, nor 

 is any known corresponding to the mica nucleus, though by heating rectorite 

 H2Al2Si20g is left. The clays may be considered as natural mechanical mix- 

 tures of the following acids and their derivatives, and possibly others : 



(1) Kaolin, . . H2 Al2Si208 • H2O. 



(2) Halloysite, . . H2Al2Si208 • 2H2O. 



(3) Pyrophyllite, . H.AUSi^Ois- 



(4) Montmorillonite, . HoAUSi^O^ 2 • ^H.O. 



(5) Nontronite, . H2Fe2Si20g • HgO. 



A classification of the silicates under this theory is given. a. j. m. 



MEDICAL NOTES. 



Year by year the importance of more liberal education for students entering 

 the medical college is more clearly recognized, and the requirements made more 

 rigid. Prof. Stanley Coulter, of Purdue University, Lafayette, Ind., recently 

 read a paper before the Indiana State Medical Society on the subject of Pre- 

 medical Education, at the close of which he outlined briefly the pre-medical 

 course as given at Purdue University : 



^'•Purpose of the Pre-tnedical Course. — The pre-medical course of Purdue Uni- 

 versity is arranged to meet a three-fold demand : 



1. To furnish a broad and liberal education. 



2. To give special and extended training in those subjects which 



underlie the strictly professional studies of the medical school. 



3. By this co-relation of work to shorten the time required to obtain 



the university and professional degrees. 



Graduates of Purdue who have completed this course are admitted to the 

 second year of all first-class medical schools, thus saving a full year. 



The preliminary work required of students entering this course is that of the 

 freshman and sophomore years of the general course, including mathematics. 



