270 



ELEMENTARY CHEMICAL MICROSCOPY 



will be at once followed by the appearance of innumerable well 

 formed characteristic crystals. If the formation of a crystalline 

 crust cannot readily be induced, the seeding of the drop may be 

 done by taking a tiny fragment of the compound from the reagent 

 bottle, crushing it to powder upon a slide and introducing an 

 infinitesimal fragment into the drop which refuses to crystallize. 

 Note-book records should include diagrammatic sketches of 

 the crystal form, extinction, extinction angles, plane angles 



^^^ 



*i w" 



Fig. 145. Note Book Sketches of Crystals. 



whenever important, etc. Fig. 145 illustrates the way in which 

 these records may be kept. 



Dr. W. W. Andrews 1 has suggested a method of recording 

 crystal systems in the note-book which will be found simple and 

 rapid. 



Isometric —I— Orthorhombic ~^r 



Tetragonal =t Monoclinic j\ 



Hexagonal >k or /\ Triclinic /^ 



Hemihedrism may be indicated by 2 written upon the symbol 

 thus, -4- =|= 



Letters to the author. Dec. 6, 1018, Jan. 4, iyiS. 



