use to indicate what can be done in the study of higher 
rank coals. Coal by nature is a flattened mass of carbon- 
ized plant debris with a comparatively small amount of 
mineral in the form of ash. Coal may be studied micro- 
scopically by four methods: the ground section with 
transmitted light; the polished surface by reflected light 
(Duparque, Koopmans); the imbedded, softened, de- 
mineralized, microtome section (Jeffrey’); and now the 
nitrocellulose peel. The most superior of these is the 
microtome method, especially good for lignitic, bitumi- 
nous, and cannel coals, but not yet adapted to anthra- 
cites. Neither the polished nor the ground section can 
be greatly magnified. The peel method is the only fairly 
quick method available, and the only method applicable 
to the study of anthracites. 
The coal specimen must be ground smooth on the 
surface to be peeled. This surface must be demineralized 
(on the surface only) by Schultze’s macerating fluid at a 
temperature of 180° F. This surface is washed with water 
and covered with a 20% solution of potassium hydrox- 
ide in aleohol. After washing again it is bathed with a 
259% solution of phenol and chromic acid. With an- 
thracite coal a 25% solution of hydrofluoric acid is used 
instead of chromic acid. After a thorough washing with 
rater, the coal is dried and smeared with nitrocellulose 
solution. 
Somewhat better peels have been made on anthra- 
cites than on bituminous coals. 
It is also well to record two difficulties encountered 
in the nitrocellulose techniques. One is shrinkage of the 
peel which takes place during drying, and which is caused 
by the evaporation of volatile materials in the solution. 
This shrinkage is partially overcome by slow drying. It 
6 . a fond re 
Sci. Conspectus, vol. 6: 71-76. 
[82 ] 
