railway receipt for the last perior for which returns are available (March, 1925), works out at 3s. 8d. per ton. We are, therefore, spending approximately £4,500,000 per annum on material which is worse than useless, since probably more than double this amount is expended in the collection and disposal of the ashes from the place of consumption to their final resting place. The consequential losses from lowering the combustion and carbonising efficiencies can hardly be estimated with any degree of accuracy, but they again will be a multiple of the figure quoted. The country's non-productive expenditure on this score may, therefore, be safely put at the stupendous figure of from £10-20,000,000, a waste which surely should be a worthy subject of the closest scientific, technical and economic examination.

INFLUENCE OF INORGANIC COMPOUNDS ON

THE FORMATION OF COAL.

To comprehend the full significance of the mineral constituents and companions of coal, the manner and conditions of its formation should be constantly kept in mind. This problem, on account of the multitude and variety of factors governing the incidence and the properties of coal deposits seems almost incapable of a complete solution and a good deal of the geological, petrographical, botanical, physical and chemical evidence on its different phases remains inconclusive.

It cannot be my task to enter into a discussion of the many hypotheses advanced to explain all or any of these phases. It may suffice to recall that ordinary coal is a compact,stratified mass of the remains of plants, which have undergone partial decay varying in character and arrested at different stages. With the exception of cannels, in the accretion of which the micro-organisms of plankton and marine fauna played a part, the practically exclusive vegetable origin of coal requires no further proof.

The principal differences between various kinds of coal are due (1) to the kind of vegetable raw material from which they were formed; (2) the conditions under which this material was accumulated; (3) the agencies by which it was decayed, and finally (4) the stage at which these biological, chemical and physical processes came to a standstill or more strictly speaking, and recognising the never-ceasing activities of nature-the stage at which these changes have arrived in our geological era.

The plant material may have varied from tree trunks down to fragments of twigs, leaves, spores, pollen, algae and microorganisms of any kind that formed the forests, swamps and other vegetation of the palæoic, or in the case of younger coals, of later periods.

The accumulation of these vegetable masses has varied locally according to their deposition in sea water, brackish water, fresh water or on land.

The resultant products of decay, apart from the material from which they are derived, and its environment, are dependent on the kind of change it has undergone; this may have been bacterial, enzymatic or purely chemical, and subject to aerobic or anaerobic, oxidising or reducing conditions, and to climatic and other physical factors, such as heat and pressure.

These four groups of factors, involved in determining the formation, structure and constitution of coal,are each and all influenced by the nature of the inorganic compounds with which the organic material is associated or in contact.

INORGANIC PLANT CONSTITUTENTS.

In the first place must be mentioned the inorganic constitutents of the plant substance, although as will be seen later, this source is quantitively the least important. The consideration of that portion of coal "ash" contributed by the plant itself, involves a study of plant physiology, and particularly plant metabolism, a subject the vastness and complexity of which does not permit of giving it here more than the most casual attention. A more detailed examination of the relation of plant ash to the inorganic constituents of coal has recently been made by P. Haas ("Fuel in Science and Practice," 1925, IV., 424), from which the intricacies attaching to the study of the ash even of present-day plants become manifest. The difficulties of interpreting the experimental results obtained from the examination of fossil coal are enhanced by the fact that we are dealing with a vegetation concerning the composition of which we can only speculate from analogy with modern plants and a vegetation the conversion of which into coal must have also affected its inorganic compounds.

The number of "essential elements " (other than carbon, hydrogen, oxygen and nitrogen) invariably occurring in plant ashes, viz., iron, calcium, magnesium, potassium, sulphur, and phosphorus, provide by their varying proportions and total

content a wide range of combinations which are added to by other elements, such as silicon, aluminium, manganese, sodium, chlorine and iodine, which are essential," but may persistently occur in some plants.

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non

Complications arise from the differences in the ash content and composition of different kinds of plants, and different parts of a given plant; thus the ash may vary from a fraction of 1 per cent. in the wood to 20 per cent. or more in the leaves, the living tissues being always higher in ash than the non-living.

Further differences are introduced by seasonal and even diurnal variations, by the nature of the soil on which the plant grows, its age, the effect of salts in the water in the case of aquatic and marine plants, of sunlight or shade and many other factors,difficult enough to elucidate by experiment with modern plants, but almost too complex to unravel from the mixture of vegetation decayed and transformed into what we know as coal.

And yet, I am convinced that the inorganic constituents of individual plant entities will form a useful guide in work on the constitution of coal, once methods are worked out for correlating them with the results from the analysis of the organic portion and the findings of microscopic examination.

INORGANIC COMPOUNDS IN THE ACCUMULATION OF COAL-Forming MatERIAL.

The accretion of the vegetable mass is subject to the influence of the conditions of accumulation. Material carried by, or laid down in salt or brackish water, covers itself with a salt solution which, after subsequent processes of evaporation or drying, leaves films of these salts upon the surface of the plant fragments. Even if a subsequent leaching-out of soluble salts with fresh water should take place, some of these will be retained by adsorption. Since the plant fragments are largely composed of colloidal substances, the electrolytes introduced with sea water cause coagulation to take place, which again tends to lock up the dissolved salts of the reacting solutions.

These phenomena must be regarded as one of the sources of the sodium chloride content of many coals which in practice shows itself as a destructive constitutent, when, as in coke ovens or gas retorts, it is voltilised and attacks, as a fluxing agent,

the refractory materials of which they are built.

Sodium chloride is, of course, not the only soluble salt which may thus be incorporated into the mass of coal-forming material, but the minor constituents of sea water play their part according to the laws of physical chemistry. For instance, the magnesium content of the dolomitic concretions known as "coal balls," must be ascribed to the magnesium chloride from sea water.

The admixture of inorganic substances. to the coal forming magma is by no means restricted to soluble salts. The water with which the plant material came into contact had in many cases mineral detritus, mostly in form of mud suspended in it. This mud became intermingled with the vegetable mass or settled on it. Where it was finely sub-divided or in form of colloidal solutions, it percolated the magma with comparative ease to be deposited by gravity or by coagulation where the chemical conditions permitted.

Whilst contact with saline solutions or mud suspensions thus caused the deposition of inorganic substances, percolating water in other cases has brought about a leachingout of the soluble plant salts and the minerals contained in the deposit. An important and as yet unexplained phenomenon is the difference between the total ash content of modern plants and the inherent ash of a large portion of most bituminous coals.

As in the adsorption or retention of salts by the peat or coal magma, so in the removal therefrom of soluble salts, colloidal phenomena play an important part. This is particularly the case where, by the decay of the vegetable debris, soluble organic compounds of an acid character, such as ulmic acid, are formed; solutions containing these, on percolating through lower layers leach out bases which are reprecipitated on continuing their downward path. In this manner a redistribution of certain inorganic compounds, notably iron and alumina, takes place, somewhat on the lines of the formation of hardpan, known to the agriculturist and forester.

In many respects the problems involved resemble those dealt with by the soil chemist, who is concerned with the first member of the chain leading from vegetable debris through peat, lignite and brown coal to bituminous coal and finally anthracite.

In the various theories evolved on the mode of decay of the raw material of coal and its degradation into a compact highly carbonaceous fuel, the function of the inorganic accessories has not yet been made the subject of close investigation. Whether the proceses of coal formation were biological or chemical, it must from analogies in fermentation practice and from experience with catalysts be expected that the mineral ingredients had a very decided influence on the course of decomposition of the organic matter. The theory of Fischer and Schrader which postulates the disappearance of cellulose by biological agencies and the formation of coal from the lignin residue, although not generally accepted in its entirety,may serve as an example, and in regard to it the observation of HoppeSeyler becomes significant that in the fermentation of cellulose, the reduction of calcium sulphate, the formation of ferrous carbonate and sulphide, and other reactions with inorganic compounds are closely connected with the degradation of the organic

matter.

or

The separation by Stopes, of four distinct ingredients from bituminous coal made it possible to enquire more closely into their mineral constituents. These coal components are: fusian, the equivalent of "mother-of-coal,' "" mineral charcoal "; durain, the dull hard coal; clarain, the portion of bright coal still containing plant debris; and vitrain, the bright coal of conchoidal fracture, originally thought to be without structure but now known to have a definite though largely obliterated structure. By the work of Stopes, Tideswell and Wheeler, Lessing and a number of subsequent workers, the differences in the microstructure of coal components were proved to be associated with characteristic differences in their hemical composition and properties, and notably in their behavious on extraction with solvents, thermal decomposition, oxidation and hydrogenation.

In particular it was shown that the four groups of ingredients varied in the amount and composition of their ash in a remarkable manner.

The ash percentages obtained from the first coal examined, the Thick Seam of Hamstead, South Staffs., were as follows: Ash per cent.

The four ashes showed considerable differences in colour and mechanical structure. That from fusain was dark brownishgrey; that from durain pure pale grey or almost white without the slightest brown tint; that from clarain a reddish-brown biscuit, and that from vitrain a pale biscuit colour. On burning large lumps, lamination is produced along the bedding planes of the coal. Clarain ash invariably contrains intrusions of grey plates indicating the presence of durain or possibly fusain, whilst vitrain also contains occasionally grey laminæ and red ferruginuous fusain, whilst vitrain also contains occasin form of a dense powder, whilst clarain and vitrain yield a light and unmistakably fluffy ash; its gossamer-like structure represents the skeleton of materials consisting to the extent of nearly 99% of combustible matter. These characteristics have been confirmed in the examination of so many coals that they must be regarded as typical for the four components and that the mere appearance of the ashes may form a useful and definite guide for their identification, with the qualification that differentiation between clarain and vitrain is not always quite easy on account of their close similarity.

GEOLOGICAL SOCIETY OF LONDON.

At the meeting held on January 20. Dr. J. W. Evans, F.R.S., in the Chair. The Stratigraphy and Structure of the Cambrian Slate-Belt of Nantlle (Carnar vonshire). By THOMAS OWEN MORRIS, B.Sc., AND PROF. WILLIAM GEORGE FEARNSIDES, M.A., F.G.S.

This paper describes the results obtained by mapping, on the 6-inch and 25-inch scales, the rocks and structures exposed over about 10 square miles of the slatequarrying district of Llanllyfni, Tal-y-sarn. Nantlle, and Moel Tryfan, in Carnarvonshire.

STRATIGRAPHY.

The Nantlle Slate-Belt is the southwestern part of the outcrop of the Cambrian rocks of Northern Carnarvonshire, which rest with appreciable unconformity upon the late pre-Cambrian volcanic rocks running south-westwards from Llanberis.

A correlation of these rocks with equiv alent rocks in Southern Carnarvonshire and Merioneth is suggested. It is argued that the Lower Cambrian sediments are landwaste from the pre-Cambrian rocks of

North-Western Carnarvonshire and Anglesey, whereas the later Middle and Upper Cambrian material was brought in from an unkonwn source away to the east and south. Ordovician sediments are faulted against the basal member of the Upper Cambrian. A buttress or Ordovician volcanic rocks flanks the Nantlle area on the south-east side; but, within the area mapped, there are only altered doleritedykes, later than most of the impressed structures, to represent (and that a very late stage in) the cycle or Ordovician. Devonian igneous activity.

STRUCTURE.

The Nantlle district was deeply involved in the making of the Devonian alpine range, the basal wreck of which is now Snowdonia, and all sedimentary material within the Slate-Belt was compelled to fold, and then to crush until, both in bulk and in detail, it began to shear and creep. The importance of progressive movement in the development of cleavage is emphasised. Cleavage in the Nantlle Slate-Belt is almost vertical. Many folds have associated with them vertical strike-faults or slides, which, by tearing the middle limbs, have increased the vertical displacement. Often stronger beds are rolled out or packed as lenticles along surfaces of slip which behave. thrust-planes. Strong rocks rise on on the north-western face of each slide, bend over, and are cut off by the next slide towards the north-west. The total displacement across individual slides, measured stratigraphically, may amount to many hundreds of feet. More boundaries of slate veins and quarry properties are determined by slides than by bedding-planes. Between

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slides the slate-beds have characteristic anticlinal structures, the synclines being suppressed. Some slides are evident surfaces of discontinuity, but the movement along many slides was prior to the completion of growth of authigenic minerals, and, as along cleavage-planes, these surfaces of slip are sealed. The scale and frequency of the folding at Nantlle is comparable with that in the mining district of Wanlockhead. The slide-blocks are longer and narrower than the strike-fault strips between Caermarthen and St. Clears; but secondary chrusting is impersistent, and not orderly as in the schuppen which affect the Cambrian rocks of the North-West Highands.

as

With removal of load by denudation,

joints and other tensional fractures have appeared. The direction of some of these is related to rock-texture, but bevels, etc., cross them at acute angles. The latest cross-faults are master-fractures, which traverse all other structures as also the preand post-Cambrian formations that flank the Slate-Belt. The direction of these is north or north-west, as the geometry of the half-dozen which cross the quarry-region suggests that block-movement was associated with northward shift on the eastern side of each. Most of the dolerite-dykes follow bevels, and two have been intruded along the latest cross-faults.

A petrographic description of the preCambrian rhyolites and of a hornblendeandesite is given, with chemical analyses. Petrographic evidence also establishes the existence of secondary (authigenic) micaceous minerals with or without recrystallised quartz in all the rocks of the Slate-Belt, and especially in those slates which are of greatest economic value. New-formed bladed chlorite is abundant in the Cambrian grits, and some of it is passing into biotite. Authigenic tourmaline in minute long prisms is a frequent constituent of both coarse and fine felspathic sediments throughout the Nantlle Slate-Belt. A discussion followed.

THE INSTITUTION OF ELECTRICAL ENGINEERS.

The Improvement of Power Factor. By EDGAR WALL Dorey, Associate Member.

The first part of the paper summarises the principal types of apparatus employed for the imrovement of power factor, and gives a description of the modern static condenser and also of types of power-factorrectifying plant that have been developed during the past three years.

The second part of the paper outlines various forms of the power-factor tariff in force in Great Britain, and is divided into two main classes; first, those based on kVA demand, and second, those incorporating a power-factor bonus and penalty on the total supply bill.

Systems of metering employed in conjunction with power-factor tariffs are briefly dealt with.

MODERN METHODS OF IMPROVING THE
POWER FACTOR.

In a paper written by the late Dr. Gisbert Kapp and read before the Institution on the 16 November, 1922, various kinds of plant

in use at that time for the improvement of power factor were described.

Auto-synchronous

and synchronous motors. It is unnecesary to enlarge further on what has already been written in regard to the use of auto-synchronous and synchronous motors, as, since the date of Dr. Kapp's paper, there has been no appreciable alteration or addition to the types then described.

Rotary Condensers.-The rotary condenser still finds little favour in Great Britain, where its field of application is very limited. The rotary condenser has a comparatively high loss, usually not less than 5 per cent., and may be as much as 7 per cent.; and when this loss is capitalised, the rotary condenser, under the conditions ruling in Great Britain, where power is mainly generated from coal, compares very unfavourably with other forms of power-factor-improving apparatus such as static condensers. Whilst in the larger sizes, say 500 kVA and upwards, the rotary condenser is, when compared with, say, the static condenser, less expensive in first cost, it is much less economical and more costly when running costs are taken into consideration.

To take as an example, a 1,000 kVA condenser equipment, the difference in losses between static condensers and rotary condensers would be of the order of at least 4 per cent. With a 12-hour working day, 300 days per annum, this would be equivalent to 144,000 units lost, and at 1d. per unit sold this is approximately £600 per annum. If this difference be capitalised it will show the static condenser installation to be by far the more economical.

BALL AND ROLLER BEARINGS FOR INDUCTION

MOTORS.

The adoption of power-factor tariffs by supply undertakings has compelled designers to produce an induction motor with a very high inherent power factor, and the introduction by many manufacturers of a.c. motors fitted with ball and roller bearings has assisted greatly to this end. The smaller the air-gap the higher is the power factor, and it is obvious that with ball and roller bearings, where the wear that is attendant upon the use of the journal bearing has not to be contended with, it is possible to use a much smaller air-gap, which is a feature of modern design.

An improvement of 2 or 3 per cent. in the power factor represents quite an appreciable saving on the supply bill where a power

factor tariff is adopted, and it would appear that ball and roller bearings will play an important part in the design of a.c. induction motors in the future, and many of the leading British makers to-day adopt such bearings as standard.

STATIC CONDENSERS.

The oil-immersed electrostatic condenser was briefly described in Dr. Kapp's paper, but it is now proposed to deal more fully with this type of apparatus used for powerfactor improvement.

Condensers of this type are manufactured in Great Britain principally by Messrs. British Insulated and Helsby Cables, Ltd., of Helsby, and the Telegraph Condenser Co., Ltd., of London. The condensers consist primarily of so-called Mansbridge plates, these comprising a length of paper coated with tin under the Mansbridge process. In the construction of condensers the Mansbridge plates are separated by the requisite thicknesses of paper used as the dielectric, the number of thicknesses being dependent upon the voltage applied across the terminals of the condenser unit. Generally speaking, each unit of the condenser has a capacity of approximately 1 microfarad, but this may be greater or less according to the special conditions obtaining on the circuit.

To take as an example a 100-kVA 600volt 50-cycle three-phase condenser; this would have a capacity of 88μF and there would be approximately 295 separate units connected in parallel on each phase, the phases themselves being connected in delta.

The two principal makers of condensers referred to above assemble the units in frames, the frames being fixed into boilerplate tanks and completely oil-filled. The modern oil-immersed static condenser, which is now the result of many years' experience in the construction and application of this type of plant, may be regarded as a very reliable and efficient apparatus for the improvement of power factor.

A good deal has been said about the risk of resonance due to the connection of static condensers, but it will be agreed that experience is the best guide, and it may be safely said that over many years no difficulty whatever has been experienced in the application of condensers due to resonance. It is not claimed that resonance may not occur under certain exceptional conditions, but under the ordinary industrial conditions prevailing not only in Great Britain, but