174 The Constituents of Banded Humic Coal. 
suggests, for most practical purposes, a classification into 
(a) bright coal, (b) durain, and (c) fusain. On the other 
hand, if the view of Bode 1 and others that clarain consists of 
an intimate mixture of vitrain and durain be adopted, the 
classification is (a) vitrain, (b) durain, and (c) fusain. As 
fusain mainly consists of free carbon, there are virtually only 
two coal-types. 2 
(6) The example of the moisture content refers to the 
Top Hard Coal. 3 
(7) The example of the pyridine-chloroform analysis is 
from the work of Dr. Stopes and Professor Wheeler. 4 As the 
amounts of the gamma- compounds are approximately the 
same, the chief differences between durain, clarain and vitrain, 
as revealed by this analysis, lie in the alpha — and beta — 
compounds. These two groups of compounds are very similar 
to each other. They are {a) infusible, (b) yield but little 
liquid products (and mainly phenols) on distillation, (c) the 
gases yielded on distillation are mainly hydrogen and the 
oxides of carbon. Gamma-compounds (a) melt at 95-100 
degrees C., (b) on destructive distillation yield about half 
their weight of liquid products (mainly ‘ resinic ’ and con- 
taining no phenols), (c) on distillation yield as gases mainly 
the paraffin hydrocarbons. It is chiefly the gamma -compounds 
(ulmo-humic acids) which confer coking properties on a coal, 
though coking is not entirely referable to them. Dr. R. S. 
Illingworth considers that to yield a coherent coke, a coal 
should contain not less than 5 per cent, of gamma- compounds 
with a C/H ratio of not less than 10. 
(8) In oxidising the ingredients by nitric acid, concen- 
trated acid, with a few drops of hydrofluoric acid, is applied 
to the sample and left from two to seven days. The reactions 
which have occurred become apparent after (a) neutralisation 
with potassium hydroxide and (b) the addition of water. 5 
(9) The example of the ulmin contents are from the work 
of Francis and Wheeler. 6 Vitrain was originally regarded 
as structureless, as, indeed, it appears to the naked eye and 
even under the lens. Structureless vitrain (‘ euvitrit * in 
1 Bode, H., ‘ Zur Nomenklatur in der Kohlenpetrographie . Kohle 
u Erz,’ Vol. 18, 1928, pp. 699-710. 
2 Thiessen, R., fourn. of Geol., Vol. 28, 1920, p. 185. Evans, M. M. ( 
L. Slater and R. V. Wheeler, ‘On Vitrain,' Fuel, Vol. 8, 1929, p. 30. 
Winter, H., Gluckauf, Vol. 63, 1927, p. 483. 
3 Winter, H., ‘ Banded Coal,' Fuel, Vol. 7, 1928, p. 52. 
4 Stopes, M. C. and R. V. Wheeler, Fuel, Vol. 2, 1923, p. 88. 
5 Stopes, M. C. and R. V. Wheeler, Fuel, Vol. 2, 1923, p. 40. 
Hendrickson, A. V., ibid., pp. 103, 156. 
6 Francis, W. and R. V. Wheeler, ‘ The Spontaneous Combustion of 
Coal : the Most Readily Oxidisable Constituents,’ Safety in Mines 
Research Board, Paper No. 28, 1926. See also Moore, B., Fuel, Vol. 10, 
pp. 205-21 1. 
The Naturalist 
