October 25, 1918. ________________________ _____________________________________ THE COLLIERY GUARDIAN. 865 the setting in, the burning, the cooling, and the drawing from the kiln, require about three weeks. As a result of repeated trials made in a tunnel kiln between 1,500 degs. and 1,550 degs., the author has proved that the duration of a good burning, according to the tonnage to be produced per 24 hours, varies from four to five days from the moment the products enter into the tunnel until the moment they go out of it. This tunnel kiln consumes scarcely one-third of the fuel consumed by the burning of intermittent furnaces. Bricks from Open-Hearth Furnaces. The examination of a number of bricks taken from open-hearth furnaces shows the influence of density and porosity on crushing resistances; they give valuable indications as to the condition of the bricks in the furnaces and the essential principles which should be obsgpfced in the management of these furnaces. It also demonstrates two very plain facts, contrary to the opinions generally approved at present—viz. : (1) It is admitted that silica products are only of good quality if they include 94 to 95 per cent, of silica. But the experiments show that the grey parts of the bricks, which contain only 85 per cent, of silica and 15 per cent, of foreign matters, are as refractory as products with 95 per cent, of silica, and that thanks to their feeble porosity, they are far superior as regards crushing resistance at all temperatures. (2) It is equally admitted that an excess of lime and of iron oxide is detrimental in silica products, and that it is only necessary to exceed the proportion of 3 to 4 per cent, for these two elements combined. But in the grey part of the bricks the proportion of these two elements varies from 10 to 14 per cent. The following table recapitulates some of the physical tests which have been made in the course of these studies:— (a) Brick of good quality. (b) Brick which cracks at high temperature. (c) Brick made with rocks friable at high temperature. (d) Brick from a Martin furnace, unattacked part. (e) Brick from a Martin furnace, brown part. (/) Brick from a Martin furnace, grey part. F 1'60 ... 5’90 ... 4 ... 2’50 ... 12 ... 9’5 ...10 ...10’5 ... 2'1 ... 0’3 9’7 ...16’10 ...12 ... 9 A B C D E Fusion points ... 1,750°... 1,730\.. 1,730°...1,730°...1,710°...l,730c Linear expan- sion at 1,710° (per cent.) Porosity (water absorbed) (per cent.) Porosity after heating at 1,710° (per cent.) Crushing resist- ance at ordinary temperature ... Crushing resist- ance at ordinary temperature after heating at 1,710° ................ Crushing resist- ance at 1,500° after heating at 1,710° ......... 121 ... 480 ... 160 ... 166 ...1,115 ...1,415 ... nil ... 52 77 ... nil ... nil ... 37 ... 52 ...138 The crushing resistance is expressed as kilogs. per sq. cm. In an appendix, particulars are given of measurements of the crushing resistances of refractory materials by the method of Capt. V. Bodin. __________________________ OUTPUT ESTIMATES FOR 1918. The Coal Controller has issued the following figures, which show a further serious falling off in the esti- mated output of coal during the first 36 weeks of this year compared with the output during the correspond- ing period of last year. The net shortage is nearly 15| million tons, or about 8’8 per cent. Output of coal. Period. ‘ 1918. 1917. Tons. Tons. 1st four weeks ended Feb. 2, 191S... 18,826,700 .. . 20,430,600 2nd Mar. 2, „ ... 19,141,600 .. . 19,881,500 3rd 99 99 Mar. 30, „ ... 18,759,700 .. . 19,840,400 4th Apl. 27, „ ... 17,698,400 ... . 18,659,200 5th 19 99 May 25, „ ... 16,856,800 .. . 20,092,600 6th June 22, „ ... 17,791,800 .. . 18,727,300 7th 19 99 July 20, ,, ... 15,780,300 ... . 18,982,800 8th 99 99 Aug. 17, ,, ... 16,042,200 ... 17,769,200 9th 99 99 Sept. 14, „ ... 17,724,600*... 19,482,600 158,622,100 ...173,866,200 158,622,100 Deficiency ......................... 15,244,100 * Provisional. It will be observed that for the four weeks ended September 14 it is estimated that 17,724,600 tons of coal avere raised at mines in the United Kingdom, as against 19,482,600 tons during the corresponding period of 1917—a deficiency of 1,758,000 tons. It is estimated that on account of disputes at collieries the output of nearly 435,000 tons of coal was lost. The stocks of coal at mines and in trucks on September 14 were about three-quarters of a million tons less than at the corresponding date of last year; 1,682,400 more tons of coal were raised in the four weeks ended Sep- tember 14 this year, compared with the output in the previous four weeks to August 17 this year—an increase of from 4 to 5 per cent. The output has steadily improved during the last three months, partly owing to the return of miners from the Army, to the stoppage of the holiday season, and to a decline in the influenza epidemic, but the demand for coal is greater than ever. Miners in many counties are responding to the appeal for increased output. During the four weeks ended September 14 last the amount of extra time worked by the miners in certain counties is shown in the following table: — Days per week. Haddington ___ 0’95 Worcester .... 0’58 Monmouth____ 0’57 Pembroke ____ 0'52 Days per week. Durham...... 0'49 Edinburgh 0’48 Northumberland.. 0'46 Carmarthen.... 0'43 _______________________________________________ REFRACTORY MATERIALS SECTION OF THE CERAMIC SOCIETY. The fifth meeting of the Refractory Materials Section was held at the Technical College, Swansea, on October 17 and 18, 1918, the chair being occupied by Mr. W. J. Jones, Deputy Controller of Iron and Steel Production (Ministry of Munitions, London). Mr J. Allen Howe, B.Sc., contributed “Notes on the Refractory Materials of South Wales (Colliery Guardian, October 18, 1918, p. 810). Magnesite. In^ his paper on “ Magnesite as Raw Material,” Mr. T. Crook gave an historical review of the subject, suggested an economic classification of magnesites, and described all the chief types from different locali- ties, besides supplying statistics, etc. Grecian mag- nesite was used for making bricks as far back as 1868, whereas at Veitsch (Styria) Spaeter did not begin to make bricks before 1880. The proposed economic classification includes four groups: — (1) Spathic breunnerite (e.c/., Styria). This is ferriferous; (2) Spathic magnesite (e.c/., Quebec, Washington, Norway); (3) Compact or cryptocrystalline magnesite (e.p., Greece, California, Italy, India, and Aus- tralia). (4) Hydromagnesite (e.c/., Atlin, British Columbia). This substance is powdery or very friable. The differences in composition are shown by generalised analyses. Descriptions in some detail are given of the various types. After coarse crushing, the fragments of breunnerite or spathic magnesite are likely to be purer than those from compact magnesite. Breunnerite loses carbon dioxide from ferrous carbonate at a rather lower temperature than from magnesium carbonate. When calcined, breunnerite becomes black, owing to forma- tion of magnetic oxide, which allows of magnetic dressing to exclude dolomite. Probably thermal con- ductivity is increased at the same time, favouring rapid uniform distribution of temperature among the sinter. The chemical and physical changes in the sintering of breunnerite may be considered to be due to (1) the cleavages permitting access of the kiln gases gases to all parts of the mass; (2) the formation of magnetic oxide of iron increasing the thermal con- ductivity ; (3) combination of iron oxide with mag- nesia to form magnesioferrite, microscopic granules of which are distributed through a matrix of periclase. A paper on “ Silica and Other Refractory Bricks” was read by Mr. G. W. Mottram (Colliery Gv ar di an, October 18, p. 808). Silica Products. The paper on “ Study of Silica Products,” by Dr. A. Bigot will be found on p. 864 of this issue. Flue Dust and Firebrick. In their paper on “The Corrosive Action of Flue Dust on Firebricks,” Dr. J. W. Mellor and Mr. W. Emery record the results of tests made in a specially designed furnace on fireclay bricks and silica bricks exposed to the action of flue dusts and other corrosive materials in the form of dust. Analyses are given of the bricks and of the flue dusts, etc. In general, penetration by the dust was found to be greater in fireclay than in silica fire bricks. In most cases the bond is attacked first, and coarser grains last. In silica bricks the depth of penetration by dust is generally less the finer the grain, and the bond offers least resistance to corrosive slag. Iron oxide under oxidising conditions does not seriously corrode silica bricks, but under reducing conditions ferrous silicate is formed and acts as a corrosive flux. The iron oxides generally corrode fireclay bricks more than silica bricks. The dusts seem to promote the conversion of quartz into low specific gravity forms of crystalline silica. The effect of dust on a refractory may possibly be tested best by moulding mixtures of the ground re- fractory and the dust (in definite proportions) in the form of cones and determining the fusing point. Standard Tests for Refractories. A report on “ The Standardisation of Tests for Refractory Materials—Part II.” was presented on behalf of the committee by Dr. Mellor. It has reference to the grading of clays, etc., according to the size of grains, and to tests for the corrosive action of flue dusts on refractories. As regards the latter, it has not been found possible to devise a satisfactory quantitative method, but useful information can be obtained by the procedure adopted for the work re- ported in the preceding paper. Grading tests may be done by sieve analysis or by elutriation analysis, the latter being particularly applicable for dividing finely ground materials (flint, etc.) and clays into fractions. For the grading of fireclays the following fractions are proposed: — _ Proposed Fractions Maximum velocity. Mm. per sec. 0'18 _______ _______ 0’30 (200*8 lawn) Residue (12v*s lawn) for Grading Fireclays. Extreme Avera .e diameters. diameters. Mm. Mm. Below 0'01 ... 0’0063 0’01 Io 0’063 ...