July 16, 1915] 



SCIENCE 



89 



Dr. Geo. I. Adams, who has been professor 

 of geology and mining at the Pei Tang Uni- 

 versity at Tientsin, China, has been appointed 

 to the faculty of the Government University 

 at Peking. 



Me. C. T. E. Wilson, F.E.S., lecturer in 

 experimental physics at the University of 

 Cambridge, has been elected to a fellowship 

 in Sidney Sussex College for a period of five 

 years. 



The board of Trinity College, Dublin, has 

 appointed Miss E. M. Maxwell, of the Eoyal 

 Victoria Eye and Ear Hospital, Dublin, to the 

 Montgomery lectureship in ophthalmology. 



DISCUSSION AND COBBESPONDENCE 



APPLICATION OF PETROGRAPHIO METHODS TO 



ANALYTICAL CHEMISTRY 



When it is considered that minerals are 

 fundamentally more or less definite chemical 

 compounds and that optical mineralogy has 

 attained a high stage of development and im- 

 portance, it is a matter of considerable surprise 

 that the application of petrographic methods 

 to general chemistry has been attempted in so 

 relatively few instances and that at present, 

 speaking generally, crystal optics is a subject 

 almost unheard of among the great majority 

 of chemists. Chemical literature is filled with 

 such vague crystal descriptions as " needles," 

 " tablets," etc., which it is hardly necessary to 

 say are almost worthless — absolutely so when 

 taken out of connection with the reactions of 

 the compounds. Crystallographic measure- 

 ments are not always possible, are tedious, and 

 lack general applicability. Microchemical re- 

 actions usually resolve themselves into simple 

 observation of the appearances of the crystals 

 formed, a procedure open to the objection that 

 in many cases very diverse substances crystal- 

 lize rather similarly. Petrographic methods 

 are open to none of these objections. In a very 

 large number of substances the optical data is 

 definitive. The methods are of general appli- 

 cability to crystalline material regardless of 

 the existence or non-existence of crystal faces, 

 and are rapid and comparatively simple. 



It is well known that the rock-forming min- 

 erals are now usually determined by micro- 



scopic examination and that it is even pos- 

 sible to calculate approximately the chemical 

 composition of a rock from the data thus ob- 

 tained. In some rather rare instances these 

 same methods have been extended to chemical 

 compounds other than minerals. In 1898 

 J. L. C. Schroeder van der Kolk^ published 

 an acount of petrographic methods and ap- 

 plied them to certain artificial salts. Otto 

 Eosenheim- by a determination of the optical 

 characters, positive or negative, of phrenosin 

 and kerasin, obtained from the brain, suc- 

 ceeded in differentiating these two substances. 

 This test was confirmed in this laboratory on 

 the same materials obtained from molds. Fry' 

 has applied petrographic methods to the deter- 

 mination of the various salts ordinarily occur- 

 ring in commercial fertilizers, and to the deter- 

 mination of mixed solids obtained in certain 

 phase-rule work,* all cases where chemical 

 analysis could not give the desired results. In 

 a very recent address before the Chemical 

 Society of Washington Dr. F. E. Wright called 

 attention to the utility of petrographic methods 

 in chemical analysis, and during this address 

 and the succeeding discussion several specific 

 applications were pointed out, notably that of 

 the differentiation of the sugars. The pub- 

 lished reports of Dr. Wright and coworkers 

 afford numerous instances of the valuable ap- 

 plication of petrographic methods to many 

 substances, especially in the examination of 

 products obtained in various melts. This work 

 can not be too highly commended. Chamot' 

 has emphasized the usefulness of the methods. 

 Eeeently the literature has been searched 

 and practically complete optical data has been 

 found for over 375 chemical individuals rang- 

 ing from simple elements to the more complex 

 inorganic and organic compounds. In addition 

 there is an immense number of compounds of 

 which some of the data is known. This makes 

 it quite possible to definitely identify quite a 



1 ' ' Kurze Anleitung zur Mikroskopisolien Krys- 

 tallbestimmung, ' ' Wiesbaden. 

 ^ Biochem. Jour., 8, 110, 1914. 

 3 U. S. Dept. of Agrie., Bui. 97, 1914. 

 * Parker, Jour. Fhys. Chem., 18, 653-61, 1914. 

 5 ' ' Elementary Chemical Mieroacopy. ' ' 



