BOOKS AND CURRENT LITERATURE 131 



which undergo a change of state when the concentration of salts is 

 lowered to a certain point. — Lawrence Whitehead. 



Structure of Coal. — Among the notable achievements of recent 

 botanical effort are Jeffrey's studies on coal. For this work a special 

 technique had to be devised, since the methods of the petrologist had 

 not proved suitable for such friable and highly compressed material. 

 The new method^ consists essentially in a preliminary swelling by melted 

 phenol or by caustic soda dissolved in alcohol, followed by treatment 

 with hydrofluoric acid and potassium chlorate (or nitric acid) for the 

 purpose of desilicifying and bleaching, after which the material is im- 

 bedded in celloidin and the sections cut bj' means of a microtome. 

 One of the first fruits^ of the new method was the proof that cannel and 

 boghead coals consist not of algae, as had previously been claimed, 

 but of spores of vascular plants. It has been found possible to dis- 

 tinguish b}" the microscope coals of different sorts and locaUties.^ 

 But more important is the light thrown on the mode of formation of 

 coal,* a matter which has been much discussed. — M. A. Chrysler. 



1 Jeffrey, E. C, Methods of Studying Coal. Science Conspectus, 6: 71-76, 

 1916. 



2 Jeffrey, E. C, The Nature of Some Supposed Algal Coals. Proc. Amer. 

 Acad. Sci.'46: 273-290, pis. 1-5, 1910. 



^ Jeffrey, E. C, On the Composition and Qualities of Coal. Econ. Geology 

 9: 730-742, pis. 19-22, 1914. 



^ Jeffrey, E. C, The Mode of Origin of Coal. Jour. Geol. 25: 218-230, 1915. 



