606 THE COLLIERY GUARDIAN. March 31, 1916. without having been thoroughly mixed with air and the products of combustion. One change in the structure under the face of the bricks lining the coke oven has not so far been men- tioned, because it occurs even in the absence of salt; but it is a change which may have its own influence in producing disintegration.. It is the deposition of fin ely - divided carbon in the pores of: the firebrick, by the decomposition of methane and other hydrocarbons pre- sent in the gas driven off from the coal during its carbonisation. Another change which has to be taken into account is the reduction, by these gases, of the iron in the firebrick from the ferric to the ferrous condi- tion, in which its fluxing poWer is materially increased. As a result of such action, any small area rich in iron will become doubly dangerous as a centre of fluxing and disintegration. Curing the Trouble. At the present moment I put forward no remedy, but would' like to indicate the line on which a cure can probably be effected, if proper'co-operation is secured between the makers of refractories on the one. hand and the coke oven builder and manager on the other. In the first place, it is advisable to minimise the amount of penetration through the face by using practi- cally non-porous material in that position. Complete exclusion can hardly be hoped for, unless a suitable glaze can be found for both brick faces 'and joints; and the repeated expansion and contraction which the face undergoes is. the very severest possible trial to the cohesion of the glaze and the material behind it. If, then, penetration occurs, the material should be one which will suffer as little as possible from the fluxing of .the. soda. Among refractories which can be obtained in any quantity, alumina and magnesia stand out as offering distinct possibilities. Alumina does combine with soda, but forms an infusible compound which is decomposed again without fusion when the temperature rises very . high. Pure alumina is very. expensive; ,and the commercial form for our purpose would be bauxite, which contains silica., oxide of iron, and titanium oxide, as impurities. Iloweyer, one very grave objection to the use of bauxite, or any similar form of alumina, for any high temperature work, is the great difficulty of “ getting the contraction out of it ” by any ordinary calcining. The use of the electrical furnace may, with alumina as with silica, give us a .material with excellent properties ; and something has already, been done in this direction. But the cost of these materials in bulk is likely for many years to come to be prohibitive. Magnesia is another refractory which offers a very high resistance to soda; but here, again, the factor of cost is against it. Thin impervious facing layers of these more expensive materials should, however, be carefully considered and tried. 1 Taking it for granted that fireclay bricks continue to be used, it is well to consider what conditions they should satisfy. In the first place, the face should be close grained, and the face and sizes made so exact as to allow the use of small joints. Then the substance should be of a composition physically and chemically best adapted to resist the fluxing action of the salt. Free silica .in the brick requires special consideration, because it may act in two directly opposite ways. If it is very finely divided, so as to bring it into effective contact with the clay material, the silicate of alumina, fluxing is enhanced. If, on the other hand, the silica grains are large, the fluxing action of the salt is mostly confined to their exterior, and a state .of affairs is readily attained in which the clay and fine silica, attacked by the salt, have formed a pasty mass, stiffened and strengthened by the silica grains. This difference in the action of fine and coarse silica is equally noticeable in its influence on the fusibility, by heat alone, of clay and clay-silica bricks. A mixture of alumina and silica containing from 80 to 90 per cent, of silica, is, whefi all the constituents are finely divided, the most fusible of all such mixtures; but the same mixture, when the silica grains are coarse, fuses more nearly with the average fusibility of its two constituents. This beneficial effect of large-grained silica is due to the minimising of its interaction with the other material present, which can only take place on the interfaces of particles. It is not that the largeness of the particles in itself increases the stiffening effect, as cam be illustrated by a simple experiment which was carried out by Mr. C. A. King, in the laboratory of the Farnley Iron Company. The problem was : Given a substance which was soften- ing slightly and bending gradually with its own weight, what size of particle could be most effectively used to counteract the bending when no chemical action was possible between the softer and the harder substances? A pitch was chosen as the slightly softened constituent, which, made into the form of a pyramid, like a Seger cone, but 8 in. higher, bent slowly until it lay .flat on its support. The stiffening constituent used was ganister; and it was added in different grades of fineness in making a set of pyramids which were placed side by side in the laboratory at the ordinary temperature, and observed. The mixings used are given below, and also the time taken for each pyramid in bending to touch :— Tinies of touching. No. I*.,....................... . ... 22 hours. No. 2f between 3 and 8 to the inch ... 4| days. No. 3f „ 8 „ 25 , „ ... 3 No. 4t „ 25 „ 50 ,, „ ... 26 No. 5f ,, 50 ,,100 „ „ ... 30 No. 6f passing through the 100 ....... 23 ,, * Pitch alone f £0 per cent, pitch and 50 per cent sand. The result of this experiment was decisive in show- ing that the .coarse-grained hard material had actually less stiffening influence on the softer pitch than an equal proportion of the . same substance in smaller grains. The admixture of ganister particles of any size did, however, effect some stiffening. , Enough has now been said, I believe^ to set -out the complex considerations, physical and chemical, which enter into this problem of refractory materials and salty coals; and if any line of either thought or action has been indicated, in however sketchy a manner, which will lead to a satisfactory solution of the.problem, not only the coke oven industry, but the other carbonising and coal using industries in general, will have an obstacle removed from their path. IRON AND STEEL FOR COLLIERY WORK.* By W. Simons. Large quantities of iron and steel are used in modern collieries, and a serious responsibility rests with the manager to see that material of good quality is used, and unless such care is exercised, loss of life and serious loss to the company may result. The’ requirements of iron and steel used in a colliery may be roughly placed under the following headings :— (1) Resistance to the stresses of shock or vibration, producing an alteration in the molecular structure, such as haulage couplings, pit tubs, draw bars, etc. (2) Chains for cage attachment. (3) Suitable material for pit tub bodies, pit tub wheels, and axles, and for structural work, such as pit head framing, cages, rails for surface and under- ground. (4) Resistance to rapid corrosion. Wire ropes are purposely excluded, the subject being- one that could be better dealt with by experts in the wire rope industry. Draw Gear Attachments. The first of these requirements is undoubtedly of very great importance in all collieries, as any failure in the draw gear attachments may have serious results, causing a runaway down a steep gradient, involving possible loss of life. It is the almost invariable practice to use the best qualities of wrought iron for all such work, it being generally assumed that, in point of fatigue properties, wrought iron is superior to those of soft steel, and is easier to weld. The manufacture of steel has in recent years considerably improved—to such an extent that engineers of British and foreign railways use large quan- tities of special drawbar steel for wagons and passenger coaches. It is a mistake, therefore, to assume that wrought iron only is suitable where the material is liable to shock and vibration. The ordinary mechanical tests taken, viz., tensile, elongation, and contraction, are of very little value as an indication of resistance of the material to shock, the best criterion being the results obtained from such a machine as Prof. Arnold’s alter- nating stress machine, and from impact tests. Another material, known as “ Armco Iron ” (some- times termed ‘ ‘ ingot iron ’ ’), which is made by the ordinary open hearth process, is very suitable for with- standing severe alternating strains. It cannot correctly be termed wrought iron, but is so called from the fact that it contains 99-84 per cent, of pure iron, which is purer than any other make of iron or steel known (om mercially; whilst owing to its purity, its resistance to corrosion is equal to that of wrought iron. The following are the analyses and tests of the shree grades of material referred to; and in the case of wrought iron, grade A is the quality with which comparison is made :— C. Mn. S. P. Wrought iron ..... 0 05 ... 0’06 ... 0*05 ... 0T5 Drawbar gear steel... 0’08 to 010... 0’33 ... 0‘036... 0’030 Armco iron ...... 0’025 ... 0’039.. 0’024... 0’009 Mechanical Tests. Breaking Elonga- Contraction strain tion at point of per sq. in. in 8m. fracture. Tons. Per cent. Per cent. Wrought iron 22’5 25 45 Drawbar gear steel . 23’5 30 50 Armco iron .. 19 to 20 . 35 65 Alternating Tests. Wrought iron ................. 230 Drawbar gear steel............ 359 Armco iron................:.... 322 BBB Yorkshire iron .......... 230 Best Swedish iron ........’.... 280 obtain exact figures of the relative merits of steel and wrought iron, so far as it can be ascertained by tests, the relative resistance of each to shock and vibration. In a paper read by Mr. J. E. Fletcher before the South Staffordshire Iron and Steel Institute, he stated : “ As is' well known, the effort required to force a fracture across a bar of iron containing slag streaks is greater than the efforts which would be required to force a frac- ture across a material of the same kind free from slag streaks or seams.” The writer was anxious to prove the accuracy of this. The result of Prof. Arnold’s tests, however, does not agree with this conclusion. At the same time it