The writer narrows down the subject of this paper to the principles of coal petrology, which, being the vital point of almost all the arguments in this field, have excited much controversy among coal researchers in Japan.
Coal is made by the geological metamorphism of organic sediments.So the writer defines coal as a special kind of metamorphic rock, or more exactly, as the organic metamorphic rock originated from the organic sedimentary rock.Therefore, he believes that the petrological study of coal should have two phases;the study of coal as sediments, i.e., coal petrography, and that of the processes of metamorphosis, i.e., coalfication.
The basis of the former study is the coal petrographical classification, and it must deal with the sedimentation of organic matters.Since this sedimentation of organic matters is more strongly affected by the degradation of organic matters than by their separation according to their size and gravity, this classification must be such as throws light upon the degradating processes.
The study of coalification degree provides the basis for a fruitful research in the metamorphism.Perhaps the most efficient approach to this study is the measurment of otical properties, especially the reflectivity of various components, for petrologists are generally used to operating microscopes.In this respect one may assume that this study is nothine but an applied field of coal physics, especially of coal optics.
Coal comprises the mixture of various macerals.Coal petrography is a branch of science which deals with the systematic description and classification of the conditions and states of such mixture.Macerals can be distinguished from each other because every maceral has its own optical properties.Therefore, the basis of coal petrography is maceral optics or optical maceralogy, which covers a branch of optics as a field of physics.In short, coal petrography is a branch of science which describes the various states of mixture applying the methods of physics, especially of optics.
Coal petrology is based on coal petrography on the one hand and on the coal physics and coal chemistry on the other hand.The fact should not be made little of thatcoal chemistry also furnishes an important scientific basis for coal petrology.
In Japan, coal chemists have not generally accepted the recognition that coal is a kind of rock.It may be said that coal chemistry could not be developed much further unless they attach importance to this recognition.

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The oxygen-oxidation of coal carried out in aqueous solution of alkaliis discussed in order to investigate the influence of reaction conditions and propertiesof acids produced.The factors of temperature, oxygen pressure, agitation and amountof alkali were completely effective for the reaction rate.Oxidation mechanism waschanged according to the ratio of alkali to coal.When less matured coal was used, oxidation rate became higher, but the yield of aromatic acids lower.From the industrialpoint of view, the most favourable method of oxidation may be sodium carbonateprocess, bleeding the reactor to remove carbon -dioxide, because of less corrosiveeffcet and possibility of easliy recovering used alkali.At optimum conditions the yieldof water soluble aromatic acids was 61% of d.a.f.coal.100parts of water-solublearomatic acids were composed of 43 parts of benzenecarboxylic acids (mainly tri-andtetracarboxylic acids), 3 parts of naphthalene carboxylic acids and about 10 parts ofbenzenoid acids having two or threerings.Butyl esters of aromatic acids were foundto have good properties as plasticizer after refining.Aromatic acids could be easilyconverted to dicarboxylic acids as tere-and iso-phthalic acids by the partial decarboxylation.
Some important problems for the design of continuous reactor are discussed, andflow-sheet and material balance in commercial scale-plant are shown.

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The authors carried out researches on the lessening of the cracking property of natural coke by the methods of weathering, powdering and preheating.
The cracking property does not decrease at a uniform rate by weathering or by preheating, but varies irregularly.Occasionally it increases more than the initial property. However, in general, the weathering is little effective for natural coke to lessen its cracking property.If natural coke is powdered by crushing, the crackingproperty decreases greatly, and if preheated about 400°C for a half hour, it vanishes
These methods do not hurt the cracking property substantially.The authors aregoing to investigate it some day.In order to measure the cracking property quantitatively, we will device a simple mechanism and use it in the experiments.

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The present writer has made it clear that the percentage of sulphur content of a coal differs remarkably from each other even among the coals produced from the same coal-field, and so lays stress on the necessity that those who propose to study sulphur content of coal should deal directly with the state of its distribution instead of its average percentage.
From this point of view, the writer made a histogram of the distrubution of sulphur content in coals at each stage of their coalification, studied the correlation which the analytical values of sulphur bear to those of H/C, 0/C, volatile matters and moisture of various coals, made other stochastical studies, and, as a consequenge, has drawn inferences as follows:
(1) Sulphur contained in coal was appended after the deposition of coal, and the histogram by its content varies according to the stage of coalification.If one classifies coals into three groups according to the rate of sulphur content-high, l ow and inbetween, the histograms show that high-oxygen coals consist chiefly of low-sulphur coal group plus a few high-sulphur coals, few of them lying between these two groups, and that, in the case of low-oxygen coals, the number of in-betweens incre se while that of high-sulphur coals decreases to the extreme degree.The decrease of hydrogen content keeps pace with that of sulphur content, and almost all the low-hydrogen belong, not to the in-between group, but to the low-sulphur group.
(2) If a coal-seam was affected by the heat of more than a certain degree of temperature, the coalification of the coals produced from it is proved to be influenced by the existence of sulphur in some ways.It promotes the decrease of the rate to of oxygen consistently, while it tends to increase that of hydrogen content, though in this latter case there are some exceptions.
(3) The sulphur content has an effect on volatile matters only inasmuch as the sulphur itself vaporizes.The writer concludes that it does not tend to decompose or condense organic matters of coals.
(4) The effect of sulphur on moisture is quite variable.

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Elastic deformation, plastic deformation and deformation in theirtransitional region of coal at room temperature have been discussed from the relationbetween Vickers hardness or micro-Vickers hardness and load.
From the above relations, a parameter of the distribution of flow units in coal has been deduced.The relation between this parameter and rank of coal is related to that between thermal decomposition range and rank of coal .
A parameter corresponding to the mechanical relaxation time has been deduced from the relation between micro-, Vickers hardness and loading time.The relation between this time parameter and rank of coal is similar to that between hardness member or Young's modulus and rank of coal.Therefore it is supposed that the relation between internal viscosity and rank of coal is similar to the above one.

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