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employ about 7000 hands. There are various other works, authoritative new solution of the problem has been including the building and repairing yards of the Clyde propounded. Speaking generally, the tendency is towards Navigation Trust. Municipal buildings, including baths, a modification of the view of which Logan, De

Origin and are being erected at a cost of £10,000. Population

Population la Beche, Dawson, and Newberry may be taken composi(1891), 9998; (1901), 18,654.

as the principal exponents, that coal seams are tion of

essentially the remains of forests upon the sites Coahuila, a state of Mexico, bounded on the N.

of their original growth, a detrital origin being supposed by the United States, on the E. by the state of Nuevo

for a part, if not the whole, of the carbonaceous material, León, on the S. by those of San Luis Potosí and Zacatecas,

which may have been derived from adjacent higheron the W. and S.W. by Durango, and on the N.W. and W. by Sonora, has an area of 62,376 square miles. In

lying land by the action of river currents.

This view, 1879 the population was 130,026, and in 1895 it was

known as the delta hypothesis, has found considerable

favour in France, especially from study of the coal-field of 241,026. The flora comprises over sixty varieties of trees of the cold and temperate zones, and fifty belonging

Saint Étienne, where the seams vary very irregularly to the hot lands. Agriculture is the principal industry, incompatible with the hypothesis of a tranquil accumu

in thickness and character, in a way which seems to be cotton, maize, wheat, beans, sugar-cane, linseed, and about

lation in situ. thirty species of leguminous plants being the chief pro

As regards the changes involved in ducts. Cattle-raising is also extensively followed. The

the actual transformation of plant structures into lignite mines are being rapidly developed, especially in the Sierra

and coal, one of the most important series of researches is Mojada, Sierra del Carmen, and in the valley of Santa

due to M. B. Renault (Bulletin de la Société de l'Industrie Rosa. The state, which is divided into five districts and

Ainérale, 3 Ser., vol. xiii. p. 865), who, starting from the thirty-three municipalities, is one of the most prosperous

study of peat, finds that the chief agents in the trans

formation of cellulose into peaty substances are saprocommercial regions of the Republic, due principally to

. its excellent railway system. The capital, Saltillo (popu- phytic fungi and bacterial ferments. As the former are lation, 26,801), is 615 miles from Mexico City by rail. It

anaerobic, the greater or less activity of either agent is has good public buildings, a State college, public library,

conditioned by variation in the water-level of the bog. &c., and is noted for its manufacture of shawls (sarapes),

The destructive agency of bacteria seems to be limited by cotton cloth, knit goods, and flour. Amongst other towns are Parras (8326), Monclova, Ciudad Porfirio Díaz, Viesca,

the production of ulmic acid of the composition, carbon Matamoros.

65.31, hydrogen 3.85 per cent., which is a powerful

antiseptic. By the progressive elimination of oxygen and Coal.—During the period that has elapsed since the hydrogen, partly as water and partly as carbon dioxide and publication of the article contained in the ninth edition marsh gas, the ratio of carbon to oxygen and hydrogen in of this Encyclopædia, the development in the methods of the residual product increases in the following manner :winning and working coal has been very considerable,

C:H. C:0. especially in the direction of increasing the output from Cellulose

7.2 individual centres of production concurrently with


1.8 general diminution in the length of the working day.

Lignite, imperfect

12.2 2:4

perfect This has been attended, at any rate in the older coal-fields, with a rapid increase in the depth of workings and greatly The constituents of lignite are generally similar to those of

а increased cost and difficulty in opening new mines, with peat, with the addition of some animal (infusorial) remains, the result that the comparatively rough methods and the degraded vegetable tissues forming a paste originally appliances of earlier times have given way to plastic, which has converted the more resisting parts of economical methods of working underground, and the plants into a compact mass. From the figures given machinery of more refined construction. The main above it will be seen that oxygen is less rapidly eliminated winding engines, especially, are now constructed upon the than hydrogen, the change to lignite being similar to that most improved types, in order to save fuel in working. obtaining in the case of peat, but further advanced. Similar improvements have been introduced in the Bituminous shale and Boghead or Torbane Hill methods of underground haulage, and horses on under- coal are considered by Renault to be mainly alterationground lines have been largely replaced by mechanical products of masses of gelatinous fresh-water algæ, which traction, the substitution of electric for steam driven by an almost complete elimination of oxygen have been motors, and the use of electric locomotives being specially transformed into substances approximating to the formulæ noticeable. In the main operation of getting or removing C,H, and C2H5, where C:H=7.98 and C:0+N = 46-3. the coal, machine-cutting has to some extent taken the place In cannel coals the prevailing vegetable constituents are of hand labour, although the progress in this direction has spores of cryptogamic plants, algæ being rare and in been more marked in America than in Europe, and even

many cases absent.

The detection of bacilli in coal is a there the proportion of the output obtained with the use of difficult matter, owing to its opacity; but by making such mechanical aids is only small when compared with that very thin sections and employing high magnification, due to hand labour. This, however, is rapidly changing, 1000 to 1200 diameters, Renault has been enabled to owing to the increased flexibility in working of electric detect numerous forms in the woody parts included motors, which will in the near future probably take the in coal. One of these, named Micrococcus carbo, in first place in this as in other branches of coal-mining. To many respects resembles the living Cladothryx found enter, however, into the details of these and other changes in the wood of trees buried in peat-bogs in process of would involve discussion of mechanical and other technical formation. Clearer evidence has been obtained from wood matters beyond the scope of the present work, which is to partially mineralized by silica or carbonate of lime included be regarded as supplementary to the article in the ninth in the coal. edition, the additional matter being noticed somewhat The transformation of woody fibre into coal is attended in the same order as that previously adopted.

with considerable contraction, which may be from 1 to 13 During the past few years the question of the origin of the original volume, but this is unequally distributed; and mode of formation of coal has received considerable it is mainly in the direction of the thickness, so that attention from geologists, but it cannot be said that any minute objects seen on the flat may keep nearly their










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original dimensions. The evidence for this is to be seen basin, which, if this be the case, would be the largest in the large number of microphotographs in the memoir coal-field in Europe. just referred to, which represents the result of twenty-one In the Rhenish Westphalian coal basin, the most years' work. Approximately the change of wood into important one in Continental Europe, great activity precoal, and the proportion of the valuable product eliminated, vails both in exploration and opening of new mines. This may be represented as follows:

is in many respects similar in structure to that of South 4(C,H1,0)=C,H,O+7CH, +8C0, +3H,O.

Wales, a large number of seams, none very thick, being Cellulose. Coal. Methane. Carbon Water.

distributed through a great thickness of strata.

These are dioxide.

folded transversely into three principal troughs whose axes The solid product C,H0 corresponds to an average

have a general north-westerly strike, but with the bituminous coal of the composition, carbon 83.1, hydrogen important difference that the carboniferous strata are 4:6, oxygen 12:3 per cent., and represents about 20 per

exposed for only a short distance along the southern cent. of the original weight of cellulose and 45 per cent. margin, the greater part being covered by secondary and of its heating power. Another aid to the study of the

tertiary rocks, which increase in thickness rapidly to the structure of coal has been found by H. M. Couriot

north. The newer sinkings have therefore to pass (Annales de la Société Géologique de Belgique, vol. xxiii. through constantly increasing depths of water-bearing p. 105) in Röntgen photography, the carbonaceous or measures, with the result that special methods of overcombustible portion being readily permeable by X-rays, coming such difficulties have been brought to a high while the mineral matter is comparatively opaque.

In degree of perfection in this region. According to Schultz this way photographs showing the arrangement of the ash

(Mittheilungen über den Niederrheinisch-Westfälischen in parallel thin bands may be obtained from a piece of Steinkohlen - Bergbau, 1901, p. 28) the proved area in coal about an inch thick when exposed perpendicularly to

1900 was 1157 square miles, estimated to contain in the planes of bedding; included masses of iron pyrites

workable seams : appear as dark spots. The suggestion has also been made

Down to 700 metres (2300 feet) to use this agent as a means of determining the proportion

11,000,000,000 700 to 1000 metres (3280 feet)

18,300,000,000 of incombustible matter in coal, the sample being ground 1000 to 1500 metres (4920 feet)

25,000,000,000 to powder and enclosed in a wooden box of a long, tapered wedge form, with a fluorescent screen along one side, which

Total within maximum working depth 54,300,000,000 becomes sensitive to the rays passing through a greater or

At greater depths

75,000,000,000 less thickness of the coal wedge in proportion to its The development of the coal-fields of the newer mining freedom from mineral matter. According to Kotte (Stahl regions can be best appreciated by the statistical table U. Eisen, vol. XX. p. 392), however, this method is compiled by Mr B. H. Brough in the Journal of the Iron unreliable for quantitative purposes, since for equal and Steel Institute :contents of ash the permeability varies with the nature of the mineral matter, a small proportion of iron being more

United Kingdom .

1900 225,170,360 effective in increasing the opacity than much larger Germany, coal

109,271,726 amounts of the ordinary ash constituents, silica, alumina,


40,279,332 &c. Thus for equal total amounts of ash, that containing


33,270,385 Belgium

1899 the least amount of iron, 0:07 per cent., gave the clearest

22,072,068 Austria, coal

11,455,139 photograph, and that with 5:4 per cent. the worst.


21,751,794 The existence of coal-fields below the secondary strata Hungary, coal

1,238,855 in the south-east of England, along the line joining the


4,292,584 Spain

1900 South Wales and Westphalian basins, as

2,680,193 Develop


13,104,000 ment of inferred by the late Mr Godwin Austen, has of



212,973 late years been verified by the discovery of Bosnia, lignite

303,425 carboniferous strata with workable coal seams


78,000 Servia,

1896 below the chalk and other secondary formations in the

11,726 Italy,

1899 388,534 vicinity of Dover, where in 1890 a borehole reached coal


239,344 at a depth of 1180 feet from the surface, and in a further Asiadepth of 1042 feet several seams were subsequently proved


4,937,000 of various thicknesses up to 4 feet. In another boring

1898 Japan

6,598,033 Borneo

1899 35,675 at Ropersole, between Dover and Canterbury, 1774 feet Africadeep, the last 197 feet are in carboniferous strata with two


1898 1,938,424 In the Dover sinking a bed of oolitic brown


1899 324,161 iron ore, resembling that of Cleveland and Luxemburg, has Cape Colony


America been discovered at a depth of 600 feet. Most extensive

United States

1900 238,877,182 developments have also been made on the eastern side of


1899 4,142, 242 the great Midland coal-field, and numerous pits have


113,191 Peru

1898 been sunk through the magnesian limestone and other


Australasia overlying strata along the whole length of the basin, from

New South Wales

1900 5,507,497 Yorkshire to Nottinghamshire. At South Carr, near Gains

Queensland .

1899 494,000 borough, in Lincolnshire, the regular succession of the


262,380 seams in the coal-field has been proved under 1700 feet of

Western Australia

54,000 Tasmania

42,000 New Red Sandstone rocks down to the Barnsley hard coal

New Zealand

975,234 at 3186 feet, the greatest depth at which coal has as yet been proved in the United Kingdom. It has been In putting down new pits, while the methods formerly suggested that the coal brought up by the trawlers on the described are generally followed, much has been fishing bank known as the Coal Pit in the North Sea, done towards accelerating the rate of work.

sinking. 65 miles east of the mouth of the Humber, may be In hard ground for instance, boring machines, derived from the eastern outcrop of the seams in this supported on radial arms attached to a central pillar, are




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3461 3360

substituted for hand labour. Twelve or more holes are application of this method at Vicq, near Anzin, two shafts bored and charged, and after the removal of the machines of 12 and 16.4 feet diameter, in a covering of cretaceous and their support to a safe height, are fired either strata, were frozen to a depth of 300 feet in fifty days, the simultaneously or in groups, the boring frame being actual sinking and lining operations requiring ninety days replaced after the removal of the broken stuff. Much

The freezing machines were kept at work for 200 time can also be saved when sinking and walling are days, and 2191 tons of coal were consumed in supplying carried on simultaneously by the method used in several steam for the compressors and circulating pumps. In deep sinkings in South Wales by Professor W. Galloway, some cases cement concrete has been usefully employed in where the bricklayers work upon a suspended platform lining shafts instead of brickwork, a layer about 10 inches with hinged flaps which completely fill the hollow of the thick being much stronger than an equal thickness of shaft when in use, but can be rapidly shifted by the brickwork. This is especially applicable to the repair of old engine at the surface as the top of the wall rises.

shafts, and also to the lining of the excavations for undermore central holes are provided with wire-rope guides, to ground pumping engines. Some excellent examples of allow of the passage of the bucket bringing up the débris this method were shown at Paris in 1901 by the Cockerill broken by the sinkers. In sinking through soft or water- Company of Seraing. The cement used, as well as the bearing strata within moderate depths, excavation by hand ballast in the concrete, was produced from blast-furnace is practised, the ground being secured with segmented slags. cast-iron tubbing and pumps or

water tubs used to With the increased activity of working characteristic of keep the bottom dry when the inflow does not exceed 6 modern coal mining, the depth of the mines has rapidly or 8 tons of water per minute. Beyond this, the water- increased, and at the present time the level of cost becomes so great that the kind and Chaudron system 4000 feet, formerly assumed as the possible limit working of boring, which has of late years been considerably im- for working, has been nearly attained. The

at great proved in detail , particularly by the addition of methods following list gives the depths reached in the

depths. for continuously removing the boring detritus, is usually deepest collieries in Europe in 1900, from which it will be to be preferred. With increase in depth, however, the .

, seen that the larger number, as well as the deepest, are in thickness and weight of the cast-iron tubbing in a large Belgium :shaft become almost unmanageable; in one instance, at a depth of 1215 feet, the bottom rings in a shaft 14. feet in Saint Henriette, Cie des Produits, Flenu, Belgium 1150 3773 diameter are about 4 inches thick, which is about the Viviers Gilly

1143 3750 limit for sound castings. It has therefore been proposed,

Marcinelle, No. 11, Charleroi

1075 3527 Marchienne, No. 2

1065 3494 for greater depths, to put four columns of tubbings of

Agrappe, Mons

1060 3478 smaller diameters, 84 and 51. feet, in the shaft, and fill up Pendleton dip workings

Lancashire 1059 3474 the remainder of the boring with concrete, so that with Sacré Madame, Charleroi

Belgium 1055 thinner and lighter castings a greater depth may be

Ashton Moss dip workings

Lancashire 1024

Ronchamp, No. 11 pit .

1015 3330 reached. This, however, has not as yet been tried. Another

Viernoy, Anderlues

Belgium 1006 3301 extremely useful method of sinking through water-bearing Astley Pit, Dukinfield, dip workings Cheshire 960 3150 ground, introduced by Messrs A. & H. T. Poetsch in Saint André, Poirier, Charleroi

Belgium 950 3117 1883, and originally applied to shafts passing through quicksands above brown coal seams, has of late years The greatest depth attained in the Westphalian coal at the been applied with advantage in opening new pits through present time is at East Recklinghausen, where there are the secondary and tertiary strata above the Coal Measures two shafts 841 metres (2759 feet) deep. in the north of France and Belgium, some of the most The subject of the limiting depth of working has been successful examples being those at Lens, Anzin and Vicq, very fully studied in Belgium by Professor Stassart of in the north of France basin. In this system the soft Mons ("Les Conditions d'exploitation à grande proground or fissured water-bearing rock is rendered temporarily fondeur en Belgique,Bulletin de la Société de l'Industrie solid by freezing the contained water within a surface a few Minérale, 3 Ser., vol. xiv.), who finds that no special feet larger in diameter than the size of the finished shaft, difficulty has been met with in workings above 1100 so that the ground may be broken either by hand tools or metres deep from increased temperature or atmospheric blasting in the same manner as hard rock. The miners are

pressure. The extreme temperatures in the working protected by the frozen wall, which may be 4 or 5 feet faces at 1150 metres were 79 degrees and 86 degrees F., thick. The freezing is effected by circulating brine (calcium and the maximum in the end of a drift, 100 degrees; and chloride solution) cooled to 5° F. through a series of these were quite bearable on account of the energetic vertical pipes closed at the bottom, contained in boreholes ventilation maintained, and the dryness of the air. The arranged at equal distances apart around the space to be yield per man on the working faces was 4.5 tons, and for frozen, and carried down to a short distance below the the whole of the working force underground, 0:846 tons, bottom of the ground to be secured. The chilled brine which is not less than that realized in shallower mines. enters through a central tube of small diameter, passes to From the experience of such workings it is considered the bottom of the outer one and rises through the latter that 1500 metres would be a possible workable depth, the to the surface, each system of tubes being connected rock temperature being 132 degrees, and those of the above by a ring main with the circulating pumps. The intake and return galleries, 92 degrees and 108 degrees brine is cooled in a tank filled with spiral pipes, in which respectively. Under such conditions work would be anhydrous ammonia, previously liquefied by compression, is practically impossible except with very energetic ventilavaporized in vacuo at the atmospheric temperature by tion and dry air.

It would be scarcely possible to the sensible heat of the return-current of brine, whose circulate more than 120,000 to 130,000 cubic feet per temperature has been slightly raised in its passage through minute under such conditions, and the number of working the circulating tubes. When hard ground is reached, a places would thus be restricted, and consequently the outseat is formed for the cast-iron tubbing, which is built up put reduced to about 500 tons per shift of ten hours, in the usual way and concreted at the back, a small which could be raised by a single engine at the surface quantity of caustic soda being sometimes used in without requiring any very different appliances from those mixing the concrete, to prevent freezing.

In a recent in current use.

Methods of


feet per

Except in modifications of details, no great alterations represented by the Harrison, Sullivan, & Ingersoll-Sergeant in the methods of working away coal seams are to be noted, machines, which are essentially large rock-drills without

the pillar-and-stall system of removal by two turning gear for the cutting tool, and mounted upon a

stages and the long-wall or continuous method working.

pair of wheels placed so as to allow the tool to work on a being representative of all the systems in use. In forward slope. When in use the machine is placed upon Europe the tendency is toward the substitution of the latter a wooden platform inclining towards the face, upon which method wherever possible, but in America pillar-and-stall the miner lies and controls the direction of the blow by a work in some form is most prevalent. In France and pair of handles at the back of the machine, which is kept Germany the method of filling the space left by the stationary by wedging the wheels against a stop on the removal of the coal with waste rock, quarried under- platform. These machines, which are driven by comground or sent down from the surface, which pressed air, are very handy in use, as the height and originally used in connexion with the working of thick direction of the cut may be readily varied; but the work is inclined seams by the method of horizontal slices, is now rather severe to the driver on account of the recoil shock largely extended to long-wall workings on thin seams, and of the piston, and an assistant is necessary to clear out the in Westphalia is made compulsory where workings extend small coal from the cut, which limits the rate of cutting to below surface buildings, and safety pillars of unwrought about 125 square hour. The chain machines reprecoal are found to be insufficient. With careful packing sented by the Jeffrey, Link-Belt, and Morgan-Gardner it is estimated that the surface subsidence will not exceed coal-cutters are similar in principle to the Baird machine, 40 per cent. of the thickness of the seam removed, and the cutting agent being a flat link chain carrying a double will usually be considerably less. The material for set of chisel points, which are drawn across the coal face at filling may be the waste from earlier workings stored the rate of about 5 feet per second; but, unlike the older in the spoil banks at the surface; where there are blast machines, in which the cutting is done in a fixed plane, the furnaces in the neighbourhood, granulated slag mixed chain with its motor is made movable, and is fed forward by with earth affords excellent packing. In thick seams a rack-and-pinion motion as the cutting advances, so that packing adds about 5d. per ton to the cost of the coal, the cut is limited in breadth (3.1 to 4 feet), while its but in thinner scams the advantage is on the other side. depth may be varied up to the maximum travel (8 feet) of In America culm and waste are washed into the workings the cutting frame. The carrying frame, while the work is by water, giving a compact mass when the water has drained going on, is fixed in position by jack-screws bearing against away.

the roof of the seam, which, when the cut is completed, are In securing the roof and sides of coal workings, malleable withdrawn, and the machine shifted laterally through a iron and steel are now used to some extent instead of distance equal to the breadth of the cut and fixed in timber, although the consumption of the latter material is position again. The whole operation requires from 8 extremely large, the forest areas of Northern Europe and to 10 minutes, giving a cutting speed of 120 to 150 Russia and other countries being laid under contribution, square feet per hour. These machines weigh from 20 in addition to native woods, to furnish the ever-increasing to 22 cwt., and are mostly driven by electric motors of quantities of pit wood required. As a substitute for 25 up to 35 H.P. as a maximum. By reason of their timber props at the face, pieces of steel joists, with the web intermittent action they are only suited for use in driving cut out for a short distance on either end, with the flanges galleries or in pillar-and-stall workings. The saving turned back to give a square-bearing surface, have been effected by the substitution of machines for hand coalintroduced by Mr Firth. In large levels only the cap cutting in English Midland collieries varies from about pieces for the roof are made of steel joists, but in smaller 9:75d. to 21d. per ton, about two-thirds of this being due ones complete arches made of pieces of rails fish-jointed at to the smaller fall of slack as compared with that the crown are used. For shaft linings steel rings of H produced in hand driving. In America the saving is less or channel section supported by intermediate struts are apparent, owing to the increased wages demanded by the also used, and cross-bearers or buntons of steel joists and drivers and assistants, and the principal advantage is in rail guides are now generally substituted for wood.

the increased rate of production, which is from 6 to The substitution of machinery for hand labour has been 7 tons daily per man underground, instead of 3 to 4 comparatively slow as compared with the changes in other tons with hand work. In 1898, 25:3 per cent. of the

directions, and is by no means general in Europe, output of Pennsylvania (15 out of 59 million tons) was

although in America the progress has been con- obtained by machine cutting, which was exclusively machines. siderable, especially since the systematic intro- confined to the bituminous coal district; the coal in the

duction of electric power underground. Of the anthracite districts is too hard and the seams too much earlier types, those with a swinging pick, imitating the disturbed to allow the cutting to be done except by action of a miner in undercutting, represented by the hand. machines of Firth & Donisthorpe and Jones & Levick, In new mines the ventilation is now generally effected have been superseded by those of the circular or chain saw by an exhausting fan, the old system of ventilating types, to which have been added others with percussive furnaces being almost obsolete. The large slowand rotatory drill cutters. In the North of England and


going fan of the Guibal type still maintains its Midland districts the circular-saw type, cutting in a character for efficiency, although the tendency is

lighting. horizontal plane at or near the ground-level, is largely towards using smaller and more rapidly-driven" used, one of the best known being the Diamond coal- machines; and the heavy casings and chimneys in brickwork cutter of Mr W. Garforth, which is similar in construction are generally giving way to lighter structures in sheet-iron. to Winstanly & Barker's machine (vol. vi. Fig. 14, Fans with curved instead of flat blades, and with spiral P. 68), but cuts to a depth of 51 or 6 feet. The Baird diffusers resembling turbines, are now largely used, that of type of chain-saw machine, working round a fixed over- M. Rateau being specially popular with Continental hanging frame, is still used in Scotland, and a modified colliery engineers, on account of its high mechanical

a form adapted for electric driving has been lately proposed efficiency. The use of small auxiliary blowing ventilators by Mr E. K. Scott (Proc. Inst. Civ. Eng. vol. cxliv. p. 247). underground, for carrying air into workings away from the In the United States percussive and chain-saw machines main circuits, which was largely advocated a few years are used almost exclusively. The former of these are since, has lost its popularity, but a useful substitute has



tion and

been found in the induced draught produced by jets of calling for special precautions. The conclusions arrived compressed air or high-pressure water blowing into at by the Royal Commission of 1891, which may be taken ejectors. With a jet of zoo-inch area, a pipe discharging as generally representative of the views of British colliery iš gallon of water per minute at 165 lb pressure per engineers, are as follows :square inch, a circulation of 850 cubic feet of air per

1. The danger of explosion when gas exists in very small minute was produced at the end of a level, or about five

quantities is greatly increased by the presence of coal dust. times that obtained from an equal volume of air at 60 lb 2. A gas explosion in a fiery mine may be intensified or inpressure. The increased resistance, due to the large definitely propagated by the dust raised by the explosion itself. extension of workings from single pairs of shafts, the

3. Coal dust alone, without any gas, may cause a dangerous

explosion if ignited by a blown-out shot; but such cases are likely ventilating currents having often to travel several miles to

to be exceptional. the upcast, has led to great increase in the size and power 4. The inflammability of coal dust varies with different coals, of ventilating fans, and engines from 250 to 500 H.P. are but none can be said to be entirely free from risk. not uncommonly used for such purposes. Electric driving 5. There is no probability of a dangerous explosion being from central-power stations has been found to be well

produced by the ignition of coal dust by a naked light or ordinary

flame. suited for this particular use.

The numerous forms of safety-lamps employed in fiery Danger arising from coal dust is best guarded against mines have received several additions in late years, and by systematically sprinkling or watering the main roads old forms have been improved and modified to meet the leading from the working faces to the shaft, where the requirements of safety in air-currents travelling at a high dust falling from the trams in transit is liable to velocity. Prominent among the new forms is the accumulate. This may be done by water-carts or hose Hepplewhite-Gray lamp, which has a conical glass sur- and jet, but preferably by finely divided water and rounding the light, with a gauze chimney, protected by an compressed air distributed from a network of pipes outer metal cylinder; the air supply to the flame is carried through the workings. This is now generally carried downwards through three tubes forming the done, and in some countries is compulsory, when the rocks standards of the cage. This, in addition to giving a good are deficient in natural moisture. According to Behrens, light overhead owing to the shape of the glass, is peculiarly the quantity of water required to keep down the dust in a sensitive to gas, and therefore valuable in testing for mine raising 850 tons of coal in a single shift was 28:8 fire-damp. Other approved lamps are the Deflector tons, apart from that required by the jets and motors. and those of Marsaut & Mueseler when specially

Mueseler when specially The distributing network extended to more than 30 miles bonneted to resist extra high-speed currents. The of pipes, varying from 31 inches to 1 inch in diameter. illuminant now generally used in Great Britain is a In all British coal-mines, when gas in dangerous mixture of rape oil with half its volume of petroleum, quantities has appeared within three months, and in all which is more suitable than vegetable or animal oil places that are dry and dusty, blasting is pro

Safety alone. In Germany Wolf's lamp, burning benzoline or hibited, except with permitted explosives, whose

explosives. petroleum spirit upon an asbestos wick, is very popular, as composition and properties have been examined giving a much better light than oil. Special care is, at the testing station at the Royal Arsenal, Woolwich. A however, required in filling, so that no free liquid may be list of those sanctioned is published by the Home Office. left in the holder; the spirit must be entirely absorbed by They are mostly distinguished by special trade names, and a filling of sponge, and any superfluous quantity poured off. are mainly of two classes—those containing ammonium Portable electric lamps, supplied by accumulators or dry nitrate and nitro-benzole or nitro-naphthalene, and those batteries, have been introduced into coal-mines; but owing containing nitro - glycerine and nitro-cellulose, which to the weight and cost, their use is as yet very restricted. are essentially weak dynamites. The safety property For the use of exploring parties after explosions, where attributed to them is due to the depression of the temirrespirable gases are encountered and compressed air perature of the flame or products of explosion to a point or oxygen must be carried, they are especially valuable, as below that necessary to ignite fire-damp or coal dust light is obtained without any demand on the air supply. in air from a blown-out shot. New explosives that are Fire-damp, when present in the air, lengthens the found to be satisfactory when tested are added to the list flame of an ordinary safety-lamp, but the effect is not from time to time, the composition being stated in all apparent with less than about 21 per cent. of gas; and for more delicate testing, special lamps with non-luminous The most noticeable feature in the arrangements for flames are adopted. In Pieler's lamp, which is of the draining modern collieries is the general abandonment of ordinary Davy form, alcohol is burned on a silk wick, and surface engines, with heavy wooden or iron rods

Pumping. a screen is provided so that the flame can be hidden. in the shaft, in favour of high-speed engines When exposed in air containing per cent., a cap of 13 placed underground, and supplied with power either by inch is formed, which increases to 2 inches with } per steam sent down from the surface, or in a less direct cent., and with 14 per cent. the lamp is filled with a deep manner by water circulating under high pressure or by blue glow. Another and more useful method is that of electric transmission. Compressed air may also be used, Dr. F. Clowes, who uses a hydrogen flame 0:4 inch long, but is mostly restricted to small installations, on obtained by attaching a cylinder containing compressed account of its low mechanical efficiency. The earlier hydrogen to an ordinary safety-lamp; the gas is turned underground steam-pumps were very wasteful machines, on into the oil flame, which is for the time extinguished, and account of the low steam pressures available and the loss relighted when the observation is finished. As little as

by condensation in the steam conduit pipes, but with 0-2 per cent. of gas can be detected by this method. improvements in construction and the adoption of multiple

The danger arising from the presence of coal dust in expansion in several cylinders with high initial steam the air of dry mines, with or without the addition of fire- pressure, the fuel consumption has been reduced nearly to Coal dust.

damp, has, since it was first pointed out by the level of that of good surface or marine engines.

Professor W. Galloway, been made the subject Several engines of this class of considerable size have been of special inquiries in the principal European countries erected in the deep Westphalian pits, e.g., one of 1900 to

, interested in coal mining; and although certain points are 2000 H.P., lifting a maximum quantity of 17 tons of still debatable, the fact is generally admitted as one water per minute 1300 feet high, with an expenditure of



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