169 
THE CONSTITUENTS OF BANDED HUMIC COALS. 
R. CROOKALL, D.Sc., PH.D. 
The complex nature of humic (so-called bituminous) coals 
long militated against research into their chemical constitution 
and biological composition, and therefore against an under- 
standing of their behaviour under various conditions and 
their most economic utilisation. 
One of the most important steps in the study of such fuels 
consisted in the recognition, by Dr. M. C. Stopes, 1 that they 
are composed of four types of visible ingredients. These 
types were designated vitrain, clarain, durain and fusain. 
Dr. Stopes’ classification has been subjected to some 
criticism, and other classifications, based on different criteria, 
have been proposed. Nevertheless, the separation of vitrain, 
clarain, durain and fusain from samples of coal and their 
investigation individually has yielded results of the first 
importance. The results have been of value both in the 
understanding of humic (and other) coals from a scientific 
point of view and in their practical employment as fuels, etc. 
The literature describing these investigations of the four 
visible ingredients has reached considerable proportions and 
the writer has summarised, in the form of the accompanying 
Table (pp. 171-173), the chief facts concerning them. 
Miners long ago recognised in humic coals ( a ) bright coal 
(‘softs’), ( b ) dull coal (‘ hards ’) and ‘ mother of coal ’ or 
‘ mineral charcoal.’ It remained for Dr. Stopes satisfactorily 
to define these, to indicate the presence of a fourth ingredient 
(vitrain) and to call attention to the importance of investiga- 
ting the constituents separately. In collaboration with 
Professor R. V. Wheeler, 2 Dr. Stopes has published the results 
of numerous researches into their nature, while other workers 
have brought to light many important facts. 
The methods by which vitrain, clarain, durain and fusain 
have been investigated include chemical analysis, resolution 
by solvents, oxidation by various agents and microscopic 
examination. The ingredients showed differences in behaviour 
of greater or lesser extent, so that it is now possible, from a 
mere visual inspection of a particular coal, to deduce certain 
of its properties and its suitability to certain purposes. For 
example, the readiness with which a particular coal ‘ cakes ' 
1 Stopes, M. C., ‘ On the Four Visible Ingredients in Banded 
Bituminous Coal,’ Pvoc. Roy. Soc., B. Vol. 35, 1919, pp. 470-487. 
2 Stopes, M. C. and R. V. Wheeler, ‘ Monograph on the Constitution 
of Coal,’ Dept, of Scientific and Industrial Research, London, 1918 ; 
‘ The Spontaneous Combustion of Coal in Relation to its Composition 
and Structure,’ Fuel, Vol. 2, pp. 29-41, 83-92, 122-132 ; ‘ The Consti- 
tution of Coal,’ Fuel, Vol. 3, pp. 3-11, 63-67, 97-105, 129-133, 179-184, 
196-204, 254-261, 288-297, 328-335, 356-360, 393-399, 439-452. 
1933 August 1 
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