February 23, 1917.

THE COLLIERY GUARDIAN.

381

have a basis of CHO, with some N, and traces of minerals
Fe, P, S, and others, either set free or still in the mole-
cules ;

(d)	That the various molecules might have been caused
to interact by the heat and pressure generated in the
earth’s crust in which they had been so long enclosed ; or,
on the other hand,

(e)	That they had been comparatively inert since their
accumulation ;

(/) That, if they had, to any great extent, interacted,
the coal might contain free carbon in considerable quan-
tity; or, on the other hand, if their interaction has been
limited, that the molecules should retain much of their
original complexity, and free carbon should be practically
absent;

(<j) That the only molecules present in coal must be
identical with those forming the various parts of plants or
those resulting from their breakdown, interaction, or
bacterial decay;

(7i) That, as cellulose, in a variety of forms, is so pre-
dominant a substance in the plant skeletal-body (the cell
walls), a greiat variety of cellulose degradation products
was to be expected in coal; and

(i)	That, as proteids in a variety of modified forms were
predominant in the living substance of the plant-body
(the protoplasm and nucleus of every living cell), a variety
of nitrogenous products were to be expected in coal, though
in very much less quantity than the former, owing to
their relatively small bulk in the living plant.

The resinic portions of coal—which, in actual experience,
figured so much more largely than (i)—were, in her opinion,
not to be anticipated as a purely logical deduction, because
resins, on the whole, were not a massive or impressive or
bulky part of the plant-body (save in special cases of
wounded conifers), and were generally distributed only in
the form of cell contents scattered in the plant tissues. On
a priori grounds, starch and its degradation products might
be anticipated as occurring in much greater bulk than
resins in coal. But, if their opinions were coloured by the
knowledge gained by experience, then resin might be anti-
cipated in considerable bulk in coals, because its exception-
ally resistant power thwarted bacterial decay, and, thus,
the resinous complexes survived, and might proportionately
increase while the plant material was accumulating, and
partly decaying in the early stages of coal formation. In
practice, therefore, they could not rid their minds of the
anticipation of a considerable proportion of resinous or resin-
degradation compounds in coal.

Research in coal did not seem to have followed these
logical deductions, and to have endeavoured to work them
out and verify them. What little was known about coal
seemed largely the result of isolated experiments, often
dependent on chance for their success, coal being an
extremely difficult and refractory substance to deal with.

Microscopic work on coal was first undertaken by three
Englishmen—Witham, who, in 1833, had a short note on
Inis coal sections, followed in the same year by Hutton, and
by Lindley, and Hutton. From the early ’fifties until
recently, little was done on the microscopic structure of coal
itself, though much was being done on the fossil plants of
the coal measures. In other parts of the world, however,
researches into coal structure were being carried on, and,
since 1900, a quantity of most important work had appeared.
Potonie, Bertrand, White, Jeffrey, Lomax, Stevenson,
and Thiessen, and others, had contributed to a rich
harvest of results. None of the previous workers had taken
quite the line of the present authors, who were making an
effort actually, and in detail,’to obtain not only a general
idea of what coal was, but a detailed knowledge of its ulti-
mate molecular structure. The palaeobotanical side of the
present work contributed the suggestion that, from micro-
scopic evidence of the extent of recognisable cellular struc-
ture in coal, Fremy’s theory that it was a structureless jelly
with accidental plant remains was wrong; on the contrary,
the various tissues which composed the plant body were to
be found—macerated perhaps, but not destroyed—in such
quantity in ordinary bituminous coal that they materially
affected its chemical composition. Hence, as different
tissues of the plant body had differing and definite mole-
cular structure, these, or modifications of these, were to be
looked for in coal. By pyridine and other solvents, the
chemists had divided coal into “ resinic ” and “ cellulosic ”
substances, the insoluble residue left after complete extrac-
tion with pyridine having hitherto baffled further investiga-
tion. By microscopic methods, recognisable spores had been
obtained from that insoluble residue, which was a first step
towards finding out its nature. Furthermore, an effort to
co-relate the various structures in the coal-forming plants
with distillation products in the coal was being made. To
do that, isolated portions of tissues all of one kind were
required, which could not be obtained from sections, but,
to some extent, had been obtained in other ways. Much
more research on those lines was required. A modem
exponent of Fremy’s “ jelly ” theory of coal said, recently,
“ You cannot expect to find calves in calves’ foot jelly.”
She maintained, however, that one could expect to find
strawberries in strawberry jam, and that the strawberries
were the source of the properties of the jam, distinguishing
it from cherry jam, for instance.

The paper was illustrated by a series of photo-micro-
graphs of the structure of various coals.

Dr. Wheeler’s Paper.

Dr. R. V. Wheeler, of the Home Office Experimental
Station at Eskmeals, Cumberland, wrote stating that the
memorandum on “ The Constitution of Coal ” would attempt
to give a complete account of the work done up to date on
the subject, and would be on the following lines :—

(1)	Definition of coal; classification of coals.

(2)	General assumptions regarding the constitution of
coal, as surmised from probable origin.

(3)	Attempts to obtain definite information as to com-
position :—(a) chemical : (i.) action of reagents, (ii) action
of solvents, (iii.) heat treatment, (b) microscopical.

(4)	General conclusions to be drawn from work done so
far; outline of future work.

(5)	Selected bibliography.

The subjoined summary did not attempt to cover the
ground indicated above, and was intended primarily as a
basis for discussion.

From the chemical point of view, one of the main objects
of an investigation into the nature of coal was to obtain
information whereby the different varieties could be so
classified that their value for different purposes was readily
apparent. Perhaps the best system of classification at pre-
sent was that drawn up by C. A. Seyler, based upon the
ultimate analyses. From a prolonged study of South Wales

coal in particular, Seyler came to the conclusion that the
typical classes of coals were confined within narrow limits
of ultimate composition; that, with coals containing less
than 84 per cent, of carbon, the percentage of carbon alone
was sufficient as a basis of classification, whilst, with coals
containing more than 84 per cent, of carbon, the hydrogen
was the chief factor in determining the character of the
coal. In that way, five main classes were scheduled, sub-
divided according to the carbon contents of the coals. A
somewhat similar classification had been proposed by
Campbell, of the United States Geological Survey, based on
the ratio of the carbon to the hydrogen percentage in the
coals. All classifications based upon the percentages of the
ultimate constituents, carbon, hydrogen, and oxygen,
ignored the fact that each kind of coal was compounded of
several different types of substances, each containing these
constituents, and that it was the proportions in which these
different types of substances were present that really deter-
mined the qualities of the coal. That fact was recognised
by V. B. Lewes, who, in his valuable book on ‘‘ The Car-
bonisation of Coal,” attempted to provide a “ rational ”
system of classification based on certain assumptions he
made as to the main ingredients of the coal conglomerate.
That was, perhaps, the only attempt that had been made to
ascribe to coals ” rational ” analyses, such as were given,
for example, to clays, and the system was worked out with
great ingenuity. It failed, however, because it was prema-
ture. The assumptions made as to the main constituents of
the coal conglomerate were not founded on fact, but the
system gave a good idea of what might be done did we
know more about the chemical compounds in coal.

The work done with a view to isolating definite chemical
compounds from coal, or, failing that, to acquire definite
knowledge as to the character of its ingredients, had taken
two directions, viz. :—

(1)	The treatment' of coal with solvents; and

(2)	Its destructive distillation under various conditions.
These two methods of attack had also been combined.
During the years 1880-1890, there seemed to have been in
France a recrudescence of interest in coal, such as there
was in England now, and, although the concern was mainly
with the origin and mode of formation of coal, much was
done towards determining its general character. On that
subject, opinion seemed to have been nearly unanimous, as
follows :—“ Coal is composed of the debris of plants
cemented together by and saturated with a humic or ulmic
substance which, after having been probably liquid or semi-
liquid, had gradually hardened, and given to the whole coal
an amorphous appearance.” They had there the idea,
which occurred again and again in the literature, that the
main constituent of coal was a humic material that had
arisen from the decomposition of the bulk of the accumu-
lated vegetable matter that was to form the coal bed, the
portions of the plants that were resistant to bacterial decay
being bound together by that humic material. As to the
exact nature of the humic material, very little seemed to
have been discovered. It would seem, from comparison
with similar material occurring in peats and lignites, to be
a mixture of compounds of much the same type arising from
the degradation of the celluloses of the plants. The parts
of the plants that would, -and did, best resist decay were
those rich in resins and waxes, or protected by resinous
or waxy coatings.

Reverting to chemical enquiry, numerous attempts had
been made to resolve coal by means of such organic
solvents as ether, acetone, and-benzene, but none of these
extracted at ordinary pressures more than 1 or 2 per cent,
of the weight of the coal; and it was not until Bedson, in
1899, discovered the remarkable solvent action of pyridine,
which dissolved .as much as 40 per cent, of some coals, that
much progress was made along that line of enquiry. Some
doubt had been expressed by recent workers whether the
action of pyridine on coal was merely solvent, chiefly because
there was undoubtedly a difficulty in removing the last
traces of pyridine from the fractions. According to his
experience, .any combination that might be presumed to
take place between the pyridine and any part of the Coal
substance was exceedingly weak, and not such as could be
held to alter the general character of the compounds con-
tained in coal. They had in the treatment of coal with
pyridine a means whereby coal could be resolved intov two
portions, differing widely in their properties. Further, if
the portion of the coal soluble in pyridine were now treated
with such solvents as benzene or chloroform, which ordi-
narily extracted little from untreated coal, prolonged extrac-
tion caused a further resolution, about 30 or 40 per cent, of
the pyridine extract being soluble in benzene or chloroform.
The third fraction, soluble both in chloroform and pyridine,
differed .markedly from the other two, and from the original
coal. It was a sepia-coloured solid, which softened, at
90degs., and parts of which melted at 102 degs. About 80
per cent, of it distilled as gases and oils at a temperature
of 900 degs. The other two portions did not differ appreciably
from one another, except in their solubility in pyridine.
They yielded very little oils, but much gas on distillation,
and the residue did not coke. It was unnecessary to enter
into all the arguments that led to the conclusion that the
soluble portion of coal represented the resinous constituents
of the coal plants, and the insoluble portions the degrada-
tion products of the celluloses.

On extracting that resinous portion with pentane, a small
quantity of paraffin wax could be isolated. Such waxes
could be obtained from many coals by direct extraction with
pentane, and he thought they must be regarded as, ’n a
sense, accidental constituents of the coal conglomerate. In
any case, they farmed only about 0-1 per cent, of the total
weight of the coal. More information as to the character
of the resinous portion could be obtained by destructive dis-
tillation experiments. Most of the material melted at 102
degs., and slight decomposition began at about 180 degs.
At 250 degs. considerable quantities of paraffin wax dis-
tilled over, while at 320 degs. large volumes of gases
appeared—the paraffin hydrocarbons. At higher tempera-
tures oils distilled, which were mixtures of paraffins, naph-
thenes, and olefines—to all extents and purposes a petro-
leum oil. None of these hydrocarbons were present, as
such, in the coal, with the exception, as already stated, of
small quantities of paraffins. Their appearance in coal
distillates at such low temperatures as 300 degs., under
conditions which precluded the possibilities of their pyro-
genic synthesis, must mean that the combinations into which
they had entered in the coal substance were very weak.
They were, most probably, loosely attached chemically to
larger and more complex groupings, consisting of the poly-
merisation and degradation products of the gums, resins,
etc., of the original coal plants. When the coal was dis-
tilled, these complex groupings remained as pitch. All

that could be said at present regarding their composition was
that they were unsaturated oxygenated compounds, the
oxygen of which was not present as hydroxyl. That left
them with CHO compounds containing oxide or ether group-
ings and double linkage. They were almost certainly cyclic
compounds.

As to the cellulosic compounds, the portion of coal
insoluble in pyridine, and the portion soluble in pyridine
but not in chloroform, yielded practically identical products
on destructive distillation. The gases were mainly hydrogen
and the oxides of carbon, and the liquids mainly phenols.
The resinic compounds yielded no phenols—one of the most
striking differences between the two compounds. The dis-
tillation of phenols from what they had called cellulosic
compounds was significant, for cellulose itself yielded
phenol on destructive distillation. They could say, there-
fore, that the degradation changes to which the original
vegetable matter of coal had been subjected—the changes
supposed to have produced the semi-liquid. humus in the
early stages of coal formation — had not, in every case,
resulted in the complete elimination of the structures of the
molecules of the celluloses. Some portions of the celluloses
might, of course, have undergone more drastic changes, -and
there was evidence that there were molecules present in
coal that contained structures similar to those present in
the carbon molecule, but there was no evidence, for the
assumption often made that free carbon was present as a
normal constituent of any coal.

The two main groups of compounds—cellulosic and resinic
—into which any coal could be divided, yielded distinctive
products of distillation. It was not a difficult matter to
treat a coal first with pyridine and then with chloroform,
and thus determine the proportion of resinic contained, and
he suggested that such a method of 'analysis—the first step
towards obtained ” rational ” analysis—would yield more
information as to the value of a coal than could be obtained
by ultimate and proximate analyses alone, and might
usefully be adopted by chemists.

DISCUSSION.

Dr. P. Phillips Bedson, Professor of Chemistry,
Armstrong College, stated that there were so many
different aspects of the chemistry of coal that it was no
simple matter to determine in what way best to attack
the problem of the nature of the substances which went
to form the complex material. He was decidedly
inclined to think that the best method of attack would
be found to be based upon a systematic separation by
the aid of solvents, and such an examination of the
several solutes as would afford more information as to
their nature than could be obtained by the study of the
products of their more or less destructive distillation.
In looking through papers dealing with the subject, he
found one by Dr. Smythe, which was printed privately,
and published in 1897. That paper contained a valu-
able contribution to the chemistry of brown coal, and
illustrated a method of attacking the problem; and,
seeing that, of late, an interest in the chemical consti-
tution of coal had revived, it was desirable that it should
be re-published. The coal was submitted to a syste-
matic .treatment with solvents, and from the solutions
some ■well-characterised substances were obtained. The
residual coal, i.e., the portion not attacked by the sol-
vents, was then oxidised by a mixture of hydrochloric
acid and potassium chlorate', yielding chlorinated pro-
ducts similar to those which Cross and Bevan had
obtained some years previously by the action of chlorine
on Wigan coal, and which they recognised as similar to
the chlorinated products obtained from lignified fibres.
The oxidation products were very complex, and their
separation and isolation were difficult. Amongst these
products there would appear to be ’ trichloracetic acids
and solids, from which, by treatment with solvents such
as ether, a complex, C22H18Cl4O10, was isolated. As
would be seen by reference to the 1896 report, similar
complex products were obtained by treatment of bitu-
minous coals. The difficulty met with in attempts to
elucidate the constitution of these chlorinated products
led to the abandonment of that line of investigation. In
the course of the examination of the action of solvents
on coal about 1899 he found pyridine a more satisfac-
tory solvent than phenol or aniline, and, in his paper
read before that section in 1908, he detailed some of the
results. These were avowedly incomplete, but he was
not without hope that, with a continuance of that
method of working, and with newer solvents, some
further insight into the constitution of coal would be
attained.

Dr. J. A. Smythe, Lecturer in Chemistry, Armstrong
College, stated that, since 1897, he had not looked at
coal, excepting in the coal scuttle, and he was afraid
that his present knowledge was considerably less than
that of 20 years ago. What little work he did on the
subject convinced him of the enormous complexity of
the problem. He treated coal with various solvents,
and got out some rather interesting bodies which seemed
to be allied to those extracted', only within the last few
years, by Pictet, who extracted coal on a very large
scale with benzene, and isolated some hydrocarbons.
One of these was a C18 body, and Pictet showed that
that hydrocarbon absorbed oxygen from the air, and
became oxidised. Another aspect of the work that the
speaker took up was the chlorination mentioned by Dr.
Bedson, and that led to formation of very complex com-
pounds indeed, one of the formula Dr. Bedson had
quoted. In a series of the things that he analysed, the
hydrogen decreased quite regularly with the increase in
chlorine. He thought that the interest in these was in ,
the large percentage of oxygen. He thought Dr.
Wheeler somewhat ill-advised to introduce the term
“cellulosic.” It was an ugly word, and implied a
knowledge they did not yet possess. He regarded Dr.
Stopes as more honest in the way that she made her
classification as a result of an a priori deduction,
more as a result of argument than founded upon a scien-
tific study of the subject. He considered that these
authors were attacking the subject in the right way by
microscopic examination and chemical study.

Dr. J. T. Dunn, public analyst, said he had done no
practical work on that subject, but had acquired a