’January 11, 1918. 11 THE COLLIERY GUARDIAN. ________________________________________________________________________________ PREVENTING LEAKAGE IN COKE OVENS.* By H. Grahn. One of the most difficult tasks in building coke ovens is to obtain completely and permanently tight joints between the coking chambers, heating flues, and the walls supporting the roof. The inner walls of the coking chambers being alternately in contact with the white hot coke and with cold, damp fresh charge, the extreme changes of temperature naturally stress and distort the bricks to a very considerable extent, so that the* joints easily loosen and the mortar drops out. This class of damage is particularly frequent in regenerative ovens with periodical reversal of heating, since those parts of the walls which are directly exposed to the flame have to stand a far higher temperature than those bathed by the more or less consumed gases, or waste heat. The increased leakage through the oven walls naturally brings about a greater amount of short- circuiting of the distillation gas in the ovens on the one hand, and the heating gas in the flues on the other; and according as the relative pressure of the two gases varies, the one gas will flow into the other, with the result that either there will be a direct loss of the coal gas by combustion, or its quality will be reduced by the products of combustion of the heating gas. Of the various methods proposed for preventing these losses, the only one which will be dealt with here is that of facing the walls with plaster, a method which at the same time allows the corroded bricks to be covered up, and makes a straight, smooth surface, thus lessening the resistance offered to the pushing of the charge, and preventing further damage to the walls. This method of protection lias been tried at the .Mans- feld pit, Langendreer, but without the desired success, owing to the failure of the plaster to hold. This was probably due to a difference between the coefficients of 25mm 'J5mm ■15mm Fig. 1. Fig. 2. expansion of the plaster and the old brickwork, the result being the formation of cracks which followed the joints of the brickwork, so that, at the end of a year, the repaired portions were again rough, whereas the adjoining unrepaired bricks had not suffered corro- sion. More satisfactory results have been obtained in other cases; but the method cannot be recommended where, as at the Mansfeld pit, lean and expanding coal is coked. Owing to the unfavourable behaviour of plaster, the manager decided to abandon the system, and worked out a new method, by means of which such an inti- mate and durable connection is established between the facing bricks and the mortar that they form a solid whole, and completely withstand the variable stresses due to the great fluctuations of temperature to which they are exposed. Fig. 3. With this object, special dove-tailed bricks were used and laid in such a manner as to form dove-tail joints on the inner face of the coking chamber (fig. 1). The facing bricks are about 0-6 in. thick, and the joints 0-6 in. at the front and 3 in. at the back. Fig. 2 is a front view of the inner face of the wall; and fig. 3 a vertical section through one of the coking chambers and the heating chambers on either side, showing that the dove-tail joints appear only on the inner sides of the coking chamber walls. The joints are filled with a mixture of two parts fireproof cement and one part ground firebrick, the brickwork having been moder- ately heated beforehand. The bricks are but little dearer than ordinary coke oven bricks, the extra cost per oven being only about £5. The mortar binds the bricks firmly together, and does not drop out of the Glliclcauf. dove-tail joints under the stresses induced by the changes of temperature. At the Mansfeld pit, five Otto ovens, which were lined in the above manner, have been in use for a year without showing any signs of corrosion or any damage to the joints. ______________ COAL TRAFFIC ON RAILWAYS AND CANALS IN 1916.* The following table shows the coal and coke carried by the various systems of railway, canal and other inland navigation companies from colliery districts in the United Kingdom in 1915 and 1916:— 1915. 1916. Railways, England and Wales :— Tons. Tons. Barry (coal) — 38 Brecon and Merthyr (coal & coke) Burry Port and Gwendreath 1,471,988 1,493,359 Valley (coal) 632,090 ... 601,852 Cardiff (coal) Cleator & Working ton Junction 10,800 ... 62,394 (coal and coke) 537,373 ... 615,407 Dearne Valley (coal and coke)... East and West Yorkshire Union 1,777,543 ... 1,978,878 (coal and coke) 610,770 ... 597,568 East Kent (coal) 15,886 ... 70,848 Furness (coal) 138,053 ... 126,646 Glyn Valley Tramway (coal) 664 ... 39 Great Central (coal and coke) ... 13,913,038 ... 14,086,958 Great Northern (coal) 8,524,741 ... 7,944,662 Great Western (coal and coke)... Great Western and Midland, 20,872,433* ... 21,768,733 Severn and Wye Joint (coal)... 1,076,339 ... 1,034,906 Hull and Barnsley (coal and coke) Lancashire and Yorkshire (coal l,812,781f ... 1,544,0401 and coke) 8,811,114 ... 8,544,005 Llanelly and Mynydd Mawr(coal) London and North - Western 228,221 ... 240,252 (coal and coke) Maryport and Carlisle (coal and 20,812,447 ... 20,899,982 coke) Midland (coal and coke, excepting 339,032 ... 349,094 gas coke) 27,477,018 ... 28,225,796 Mumbles (coal) 22,992 ... Neath and Brecon (coal) '.. 1,008,887 : 919,605 North-Eastern (coal and coke)... North Staffordshire (coal and 34,413,617 ... 34,517,497 coke) 3,374,650 ... 3,488,408 Port Talbot (coal and coke) Rhondda and Swansea Bay (coal 4,773,945 ... 1,657,179 and coke) : 886,417 ... 1,021,069 Rhymney (coal and coke) 4,507,049 ... 4,841,519 South-Eastern and Chatham (coal) 94,503 ... 146,492 South Wales Mineral (coal) South-Western and Midland, Somerset and Dorset Joint Line 276,040 ... 292,177 (coal) South Yorkshire Joint Line 380,040+ ... 381,1501 Committee (coal and coke) 918,735 ... 943,064 Taff Vale (coal and coke) Railways, Scotland:— 12,885,194 ... 12,904,546 Caledonian (coal and coke) Campbeltown and Machrihanish 11,130,211 ... 11,490,559 Light (coal) Glasgow and South - Western 16,019 ... 22,937 (coal) 3,267,430 ... 3,304,502 North British (coal and coke) ... 17,374,699§ ... 17,222,861|| Railways, Ireland:— Cavan and Leitrim (coal) Great Southern and Western 7,034 ... 8,895 (coal) Canals, England:— Aire and Calder Navigation (coal 7,765 ... 16,106 and coke) 1,920,309 ... 1,528.831 Ashby (coal) 38,328 ... 43,183 Ashton (coal) Birmingham Canal Navigations 55,524 ... 51,366 (coal and coke) Bridge water (coal, including a 3,528,086 ... 3,612,571 small quantity of coke) Calder and Hebble Navigation 360,733 ... 364,355 (coal) 94,060 ... 93,042 Chesterfield (coal) 14,145 ... 14,130 Cromford (coal) 24,901 ... 28,221 Erewash (coal) 27,154 ... 26,231 Huddersffeld (Broad) (coal) Leeds and Liverpool Canal Com- pany (coal, including a small 30,432 ..• 25,512 quantity of coke) 765,000^... 768,0005[ Macclesfield (coal) Manchester, Bolton and Bury ' 8,110 ... 8,035 (coal and coke) 320,131 ... 319,227 Nottingham (coal) 16,544 ... 16,727 Oxford Canal Navigation (coal) Sheffield and South Yorkshire 25,695 ... 25,959 Navigation (coal) 310,451 ... 251,010 Shropshire Union (coal and coke) Staffordshire and Worcester- 16,218 ... 14,302} shire (coal and coke) Stourbridge Extension (coal and 162,204 ... 145,556 coke) 64,416 ... 68,270 Swansea (coal) Trent and Mersey Navigation 59,047 ... 58,397 (coal and coke) 173,336 ... 171,641 Trent Navigation (coal) Canals, Scotland:— 138 ... 83 Forth and Clyde (coal and coke) 136,345 ... 155,686 Monkland (coal and coke) 57,950 ... 60,695 Union (coal and coke) Canal, Ireland:— 15,306 ... 12,098 Grand (coal) 161 ... 669 * Revised figures. f Including patent fuel, ended October 31. I Year § 1,211,578 tons of this quantity were conveyed to Burntisland Dock and 1,745,262 tons to Methil Docks for shipment. || 873,581 tons of this quantity were conveyed to Burntisland Dock and 1,651,627 tons to Methil Docks for shipment. Approximate. ______________ * From Part III. of the General Report on Mines and Quarries, 1916. _____________________________ Supplies of Gas Coke in the Metropolitan Area.—Owing to the presence of large stocks of gas coke at London gas works, the Controller of Coal Mines has agreed that any consumer who has already put in some form of requisition for coal or coke under the Household Coal Distribution Order, 1917, may purchase in addition, either directly or through his coal merchant, a supply of coke not exceed- ing five tons, provided that arrangements can be made for delivery before February 1 next. This supply of coke is additional to any quantity included in the allowance under the requisition, and must be gas coke manufactured within the Metropolitan coal area. THE REFRACTORY PROPERTIES OF MAGNESIA.* By H. Le Chatelier and B. Bogitch. Magnesia is now largely employed in the manufacture of high grade refractory materials, the use of which in steel works has kept pace with the development of the basic process. In this process, the refining of the metal is effected in presence of a slag rich in lime—that is to say, highly basic, the result being to eliminate not only carbon, silica and manganese from the cast iron, but also phosphorus, which cannot be removed in the presence of a slag rich in silica, i.e., of acid character. It would be impossible to make use of basic slags in a furnace lined entirely with silica or clay bricks, as these materials weaken too quickly in the presence of lime. Magnesia bricks, on the contrary, being themselves basic in composition, offer complete resistance. In all basic furnaces the lower part of the vertical walls, and often the sole itself, is built of magnesia, the arch, however, being always composed of silica bricks. Magnesia bricks are extremely refractory. Pure magnesia melts only at a temperature of 2,400 degs., or thereabouts—a temperature 700 degs. higher than that of the steel furnace. Still, pure magnesia is never used in the manufacture of bricks, variable proportions of iron oxide being added—an addition of which gives to the bricks their brownish hue. This iron may also be present as carbonate, in the raw material, isomorphi- cally mixed with the native carbonate of magnesia. The brick also contains silica and a little alumina, derived probably from the magnesium silicates asso- ciated with the coal, or else from the ash of the fuel used in the firing process. All these impurities necessarily increase the fusibility of the mass. The writers, in giving their conclusions after tests on the refractory properties of magnesium bricks, add the comparative results of their experiments on a ferro-chromium brick. In building the furnaces such brick is employed, in order to separate magnesium bricks from the silica bricks, since the direct contact of the basic and acid materials would provoke mutual fusion. Ferro-chrome, on the contrary, acts neither on the silica nor on the magnesia bricks. The test pieces were the ordinary bricks or specimens made at the laboratory. To obtain a standard for comparison, an attempt was made to prepare a block of very pure magnesia by melting the precipitated mag- nesia in the electric furnace; but, at the high tempera- ture necessary for this fusion, the lime of the furnace walls and the impurities present volatilised and affected the mass. Therefore, a combined mass containing only 94 per cent, of magnesia—just about equal to a well- made factory brick—was obtained. The following is a list of the test pieces:—(I.) Styria brick, baked at 1,450 degs., made in 1890, ordinary quality ; (II.) Eubee brick, made in 1910, good quality; (III.) Brick G, good present day manufacture; (IV.) Brick B, mediocre quality, made with 3 per cent, of roasted pyrites added to the paste ; (V.) pure magnesia, melted in the electric furnace; (VI.) premier matter for B agglomerated in the electric furnace; (VII.) ferro- chrome brick. Chemical Analysis. I. II. III. IV. V. VI. VII. Magnesia ... 86’7... 93*4... 89*4... 81*2... 93*7... 88’5... 12*3 Lime ....... 1’0 3’7... 4’5... 4’8 .. 2’7... 4’5... 5’8 Iron oxide (Fe2O3) ... 6’0... 0’5... IT... 4’2... 0’3... 1’4..*15'5 Alumina..... 0 6... 0’2... 0’8... 1’0... IT... 0’0... 10’9 Silica ....... 6’7... 28... 4’2... 8’8... 3’2... 6’5... 4’7 Chrome oxide . — ... — ... — ... — ... — ... — ... 50’0 Manganese ,, — .. — . — ... — ... — ... — ... 1’5 Totals...... 101’0...100’6...100’0...100’0...101’0...100’9...100’7 * FeO. Crushing Strength. (Kilogrammes per square centimetre.) mperati ire, degs. Cent. 15...1,000...1,300...1,500.. .1,600 I 145... 85.. 66... 3'6.. . 1’8 II 420... —... —... 185.. , 8 Ill 390... —... —... i>90.. . 4’8 IV 230... —... —... 16.. . 3’5 V — ... —... —... >90.. . 6'6 VI 530... —... —... — .. . 3’5 VII 260... 120... 6... 2.. . 1 In further experiments carried out on Nos. I. and II., there appeared a sharp decline in the crushing strength for the Styrian brick (the less pure of the two, between 1,300 and 1,400 degs., and the same for the Eubee brick, 1,500 and 1,600 degs. All magnesia bricks exhibit this sudden drop in resistance at a more or less high tem- perature, according to their degree of purity. It would appear as though, at a high temperature, the foreign ingredients suddenly melt in such a way as to leave the grains of magnesia isolated in the molten magma; they are then like wet sand, and possess only a feeble mechanical resisting power. The best magnesia bricks exhibit at 1,600 degs. a crushing strength much inferior to that of good silica bricks. Moreover, at these high temperatures deformation of the magnesia bricks is to be expected as with clay bricks, but they give way gradually instead of breaking abruptly like the silica type. In cooling the weakened part resumes its hardness after the solidification of the molten magma. The results of the experiments explain why magnesia bricks in furnace linings present less resistance than silica, although their fusion temperature (when sheltered from all mechanical stress) may be remarkably higher, 2,050 degs. Cent, instead of 1,750 degs. The rate of the drop in resistance observed in the ferro-chrome brick is analogous to that of the magnesia, with a much lower temperature for rapid loss of solidity —viz., 11,000 degs. instead of 1,350-1,550 degs., according to the purity of the magnesia. * From a paper presented to the Academie des Sciences Paris. _____________________________ Staffordshire Iron and Steel Institute.—The third meet- ing of the session will be held in the institute, Wolver- hampton-street, Dudley, to-morrow (Saturday), com- mencing at 6.30 p.m. A paper on “ Malleable Cast Iron/" by Mr. E. Adamson, of Sheffield, will be read.