1324 THE COLLIERY GUARDIAN December 24, 1914. Other Forms of Split Conductor.—It is not essential that the conductor should be divided into equal sections. If one section be made smaller than the other, say, reduced to a single wire, this wire may be carried always within the other portion which will surround it. Any fault to earth or between phases must occur on the outer portion; thus it is unnecessary to provide for excess current in the inner portion. We may now substitute a relay of the balanced type shown in fig. 11. We connect the restraining coil to the inner wire and the operating coil to the outer con- ductor. The relay may be biassed to an extent which fully covers all possible unbalancing, thus removing all occasion for balancing tests. This arrangement is not quite so good as that above described, as the trans- formers cannot be constructed with bar primary wind- ings, that for the fine wire requiring a multiple-turn primary. On small installations, such as colliery and industrial plants, where the conditions accompanying short circuits are not so severe as they are on the large power supply schemes, this objection disappears, and advantage may be taken of the cheapening of the cable and the elimination of balancing. This applies equally where such plants receive supply from the power com- panies, as the severest short circuit conditions are only met with near the generating stations. ■ Fig. 24. Fig. 25. Fig. 24.—Pote-line construction for double overhead line with split conductors. Fig. 25.—Details of insulator. The balancing problem now presents no difficulties, although in the experimental stage some were experi- enced. It is necessary to balance both the reactance and the resistance of the twin conductors, as it is the vector difference which is operative. This requires no attention in overhead lines, and is successfully accom- plished by the adoption of simple precautions in the manufacture of the cables. The Ideal Combination of Apparatus. Whilst a number of devices have now been considered, some of them by no means simple in design or appli- cation, it will be found that to meet all the ordinary and emergency requirements of electric supply there are now available a series of devices simple in character, well proven in service, and giving a degree of protection hitherto quite unattainable. The series is as follows :— (a) For the protection of all closed feeder circuits— the split conductor system. (b) For the protection of all open-ended feeder circuits, including individual motor circuits, isolated transformers, rotary converters, and the like — the core balancing system. (c) For the protection of generators and banks of; transformers—the circulating current system. Grimsby Coal Exports.—Returns for the week ending December 18, show that the coal exported from Grimsby totalled 10,939 tons foreign, against 24,270 tons foreign and 640 tons coastwise for the corresponding period of last year. Shipments :—Foreign : To Copenhagen, 1,164; Dieppe, 370; Gefle, 1,647 ; Horsens, 657 ; Kallundborg, 2,063 ; Klagshamn, 1,667; Mahno, 274; Stugsund, 1,038; and Ystad, 2,059 tons. Coastwise, nil. Immingham Coal Exports.—Returns for the week ending December 18, show that the coal exported from Immingham consisted of the following :—Foreign : To Dieppe, 2,959 tons; Fecamp, 1,571; Gothenburg, 1,769; Landscrona, 1,630; Oxelosund, 2,473; Skien, 813; Rotterdam, 6,550; and Warburg, 1,559—a total of 19,324 tons compared with 41,658 tons foreign and 8,920 tons coastwise for the corre- sponding period of last year. Coastwise nil. Hull Coal Exports.—The official return of the exports of coal from Hull to foreign countries for the week ending Tuesday, December 15, 1914, is as follows :—Amsterdam, 509 tons; Bordeaux, 3,745; Copenhagen, 1,196; Dieppe, 573; Dunkirk, 2,471; Malmo, 2,637; Middlefart, 1,290; Oxelosund, 2,025; Rouen, 18,171; Rotterdam, 700; Soder- telje, 1,647—total, 34,964 tons. The above figures do not include bunker coal shipments for the British Admiralty, nor the Allies’ Governments. Corresponding period December 1913, total 100,639 tons. Coal Mining in the State of Pennsylvania.* By SAMUEL DEAN. The outcrops of anthracite coal were probably discovered in the Wyoming Valley in Pennsylvania by the “ Yankees,” shortly after they settled there in the year 1762. Records show that much difficulty was experienced in igniting or burning anthracite, thus preventing for a long time its general use in place of wood. The public gave it the name of “ stone coal ” or “ black rocks,” and it was the subject of much suspicion and ridicule, the difficulties of finding purchasers being equal to the difficulties of reaching the market. In 1803 two “ arks ” of coal containing less than 100 tons each reached Philadelphia after a perilous passage down the Lehigh and Delaware rivers. After much delay the city authorities purchased the coal for the purpose of generating steam for a pumping plant. The trial was a failure, and the coal was broken up and used to “ gravel ” the footwalks of the grounds. In 1812, anthracite coal was successfully burned for practical purposes in the city of Philadelphia, the “mystery” having been solved by accident. With much perseverance and persistent determination the workmen had poked it, stirred it, and blown upon the surface through open furnace doors. Dinner time having arrived, the men shut the furnace doors in disgust. On returning from dinner they were surprised to find the doors red hot, and on opening them saw a glowing mass at white heat. From this time anthracite found friends and advocates in Philadelphia. According to Mr. E. W. Parker, of the United States Geological Survey, the year 1820 is, however, considered to mark, the beginning of the anthracite industry, 365 long tons having been shipped from the anthracite region in that year. In 1840, 464,826 short tons of bituminous coal were mined, and this is the first record of bituminous-coal production in Pennsylvania. In 1880, the total production of bituminous coal and anthracite was 44,538,972 short tons (2,000 lb.). The following table relating to the year 1913 shows the rapidity of development:— Coal Production in Pennsylvania in 1913. Anthracite. Bituminous. Totals. Total production, in short tons (2,0001b.).. 91,626,964 ..172,965,659...264,592,623 Production by machines— Compressed air Electricity 56,907./ 24.260.320.. 66.707.691.. . 24,260,320 . 66,764,598 Number of employees underground Locomotives under- 128,667... 156,274 284,941 ground- Steam 607... 148.. 755 Compressed air 161... 168.. 329 Electricity 781... 1,933.. 2,714 Figs. 2 to 5.—Hirsch Electric Cap Lamp. Fig. 3.—Battery Case. Fig. 2.—Battery. A, cover; B, vent tube ; C, vent plug; D, cover supports i glass); E, sealing com pound; F, e'ectrolyte: G, positive grid; H, positive lead (glass covered ; G-H, positive plate < formed with lead attached); I, positive terminal clip; J, negative grid ; K, negative lead (glass covered, with term nal screw); J-K, negative plate (formed with lead attached); L, negative contact screw ; M, wooden separator; N, separator frame (rubber); O, perforated-rubber separa- tor ; P, rubber jar. A, aluminium case; B, handle ; C, handle clips; D, positive box contacts, rivets included; E, side spring, rivets included; F, rivets; A-F, aluminium case with B, C, I), and E assembled, and all holes punched; G, angle insulator; H, negative spring; I, bolt for nega- tive spring-; J, nut for negative spring: K, screw for negative spring ; L, three screws for angle- insulator; G-L, negative spring mounted on angle-insulator with L; M, receptacle block ; N, two screws for block; O, brass ferrule for holding spring contact; P, contact spring; Q, receptacle for attachment plug; R, two top screws for receptacle; S, one lower bolt; T, nut for lower bolt; Q-T, receptacle and all screws; U, asbestos pad ; V, wire band for battery; V-W, wire band and ring ; W, ring for V. The area of what are called the “ anthracite ” fields, which lie in the east central part of the State, is 480 square miles. The bituminous seams underlie the greater portion of the western half of the State, and cover about 14,200 square miles. The Pittsburg seam is perhaps the most famous coalseam in America. It covers an enormous area, and is suitable for the pro- duction of coke, gas, and steam. Anthracite coal is now used principally for heating hotels, apartment houses, office buildings, &c., and the increase of production will probably be regulated by the increase in population. The future production of bituminous coal will be governed by the progress in manufacture. Anthracite mining is more profitable than bituminous mining. A ton of bituminous mine- run coal can be bought in the Pittsburg district for less than 4s. 91d. (1'25 dols.) f.o.b. railway cars or trucks at the mine. The price in some other parts of the State is not more than 4s. 2d. (I dol.) per ton. * From a paper read before the North of England Institute, of Mining and Mechanical Engineers. Many complaints are heard regarding the low prices, but these conditions will continue as long as the present methods are followed. Methods of Working. The room-and-pillar method of working—which some- what resembles the South Wales single- and double- stall systems—has been described in previous papers, and special reference is directed to the report by Mr. H. M. Chance to the Second Geological Survey of Penn- sylvania,* and the contribution of Mr. H. H. Stoek in the Twenty-second Annual Report of the United States Geological Survey,f for particulars of working the thick and highly-inclined anthracite seams. The working of the anthracite seams, which pitch at all angles from the Fig. 1.—Two-stage Compressed Air Locomotive IN USE AT THE VESTA No. 5 MINE. horizontal to the vertical, are gaseous, and often heavily watered, naturally demands engineering skill above the ordinary. The difficulties encountered are far greater than any met with in connection with bituminous mining. The consequence is that the cheap and incompetent owner and manager is kept out of the field to a large extent, and the industry is, on the whole, remunerative. Where the thick seams crop out and the crests of the anticlines are near the surface, and where pillars were left many years ago in shallow seams, the overburden is now being removed by means of steam shovels. It is practicable and profitable to remove 3 ft. of overburden, 60 per cent, of which is rock, for the recovery of one vertical foot of coal. On some of the large “ strippings ” the cost of removing earth has been lOd. and rock Is. 8d. per cubic yard. The Mammoth seam is 50 ft. thick in places, and on the above basis it would be profitable to remove 150 ft. of cover to win this seam. The anthracite screening, washing, and sizing plants, Fig. 4.—Cord. A, socket; B, bracket; A-B, head- piece ; C, socket insulator; l», ferrule; E, contact spring; F, insulated wire; C- K, insulated wire, spring contact, and insula- tor; G. flexible tube; H, attach- ment plug; I, bayonet pin; H-I, attachment plug with pin as- sembled; J, plug cover; K, plug insulator bushing; L, fibre washer; M, contact; J-M, plug cover complete ; N, strain spring; O, cap plate; B, back; O-P, cap plate and back ; Q, number tag; R, insu ating washer. Fig. 5.—Reflector. A, inner shell (aluminium) ; B, circuit-breaker spring co lar; C, circuit-breaker spring; I), lamp socket; A-D, A. B, C, and D assembled; E, hard- rubber insulator tube; F, hard-rubber insulator ring; G, intermediate shell; H, outer shell; I, bayonet pin; J, insulator plug; K, hexagon contact bolt; L, square con- tact nut; M, circuit-breaker glass; N, soft-rubber casket; O, convex glass front; P, screw-cap ; Q, lamp-bulb ; R, ins lating washer. known as “ breakers,” were formerly constructed of wood, but those of recent construction are of either steel or concrete, or a combination of both. Reinforced concrete railway bridges are also being built. It will be noticed that the breakers are some distance from the shafts, in accordance with the anthracite mine law of Pennsylvania. The burding of the Avondale breaker in 1869, which was situated over the shaft, caused great loss of life, the smoke being carried down into the workings. The removal of the screening-plant, therefore, is not on account of dust, as the Pennsylvanian anthra- cite dust is not considered to be explosive. It is common to wind or hoist the mine cars or tubs up above the ground level of the shaft; self-dumping * Second Geological Survey of Pennsylvania; Report on the Mining Methods and Appliances used in the Anthracite Coalfields, by H. M. Chance, 1883. + Twenty-second Annual Report of the United States Geological Survey to the Secretary of the Interior, 1900-1901, Part III.—“ The Pennsylvania Anthracite Coal Field,” by H. H. Stoek, page 61.