June 23, 1916. THE COLLIERY GUARDIAN. 1189 CURRENT SCIENCE Composition of Rock Gas. In the May number of American Institute of Mining Burrell and W. Gauger report on the composition of .the gas occurring in Cripple Creek mines. The escape of gas from the rock strata into these mines is a menace to life and to mining. The outflow (supposed by Lindgren and Ransome to represent the last exhalations of the extinct Cripple Creek volcano) is largely influenced by outside .atmospheric pressure, because it is confined in the rocks under very low pressure. At a few mines a pressure system of ventilation has been installed to assist ■ the ordinary natural circulation. Under this system air is blown into the mines by a fan placed at the top of the shaft, thereby placing the mine workings under a little pressure, at some places equivalent to 6 or 7 in. of water (about 0*5 in. of mercury). This method assists very materially in keeping the gas forced back in the rocks. It was impossible to secure samples of the pure gas as it issued from the rocks, and a sample containing 2-69 per cent, of oxygen (Cresson mine) was the one contain- ing the largest percentage of the rock-strata gas that could be obtained, though had it been possible to penetrate 15 or 20 ft. farther into the drift a sample practically devoid of oxygen would have been secured. A number of samples containing the smallest percentages of oxygen were recalculated, in order to determine the actual composition of the gas as it issued from the rocks. This calculation showed that the gas contained between 12-03 and 18*37 per cent, of carbon dioxide and 81*63 and 87-97 per cent, of nitrogen. The average of all the results was 13-87 per cent, of carbon dioxide and 86*13 per cent, of nitrogen, or, in round numbers, 14 per cent, of carbon dioxide and 86 per cent, of nitrogen. The gas, therefore, as it occurs in the rocks is a mixture of carbon dioxide and nitrogen, with the latter much in excess. The bad effects on life and lights are principally due to the fact that the rock gas so dilutes the air of the mines that the oxygen falls to a point where lights will not burn or so low that life is endangered. Symptoms of distress in men do not usually begin to appear until 3 to 4 per- cent. of carbon dioxide is present, whereupon the breathing becomes affected. Mien can go on working for a considerable time in such an atmosphere , although they will certainly become more quickly fatigued. Carbon dioxide affects the so-called respiratory centre in the brain, and makes a man breathe a larger volume of air over a given time than if no. carbon dioxide were present. While air with so small an amount of carbon dioxide as 2 per cent, may be breathed with comparative safety and no great discomfort, at the same time the efficiency of the workmen is lowered. In addition to the work a man may be doing in such an atmosphere, he is handicapped by being forced to breathe a larger volume of air over a given time—a feat that consumes energy just as his work of drilling a hole in the rock or loading ore consumes energy. When the oxygen in air is gradually reduced, very little effect may be noticed before the occurrence of impairment of the senses and loss of power over the limbs. If the reduction be gradual and the symptoms carefully watched, it will be noticed that at about 12 per- cent. of oxygen (that is, with a reduction of about 9 per- cent. from the composition of atmospheric, air) the respirations become just perceptibly deeper and more frequent, and the lips slightly bluish. Distress increases with continued decrease of the oxygen until with 6 or 7 per cent, there is marked clouding of the senses and loss of power over the limbs, which would end sooner or later in death. In a test of this kind it was found that a man lost consciousness when the oxygen dropped to about 7y per cent. ' As the oxygen in air decreases, the illuminating power 1' of lights diminishes, until, in the case of the ordinary i| oil-fed lamp wick such as a candle or miner’s oil torch orqg the Transactions of the Engineers, Messrs. G. A. safety .lamp, the flame becomes extinguished at about 17 J' height of a vertical retort bench, 21 ft. over all. A large per cent, of oxygen, and the acetylene flame at between 12 and 13 per cent, of oxygen, i.e., if a candle flame goes out the oxygen content of the air is less than 17 per cent., and if the acetylene flame goes out the oxygen content is less than between 12 and 13 per cent. This effect is almost entirely due to the oxygen content, and even in the Cripple Creek mines, where the carbon dioxide may be from 5 to 10 per cent., in atmospheres that extinguish flames, it exerts only a minor effect. Men should not work where candles will not burn, and should not be solely reliant upon the acetylene flame for guidance regarding bad air. The acetylene flame will burn in air where the oxygen is only a few per cent, above the proportion that is very dangerous to life, hence only a small margin of safety is assured. Eight of the samples contained traces (0’01 to 0-03 per cent.) of combustible gas, apparently methane (CH4). The proportions were so small, however, as to be insignificant. Conditions of temperature and humidity were good in those mines where samples were collected. Grain-Size Measurements in Metals. According to the amorphous cement theory, all metals and alloys in the solid state are mixtures of the crystal- line and amorphous phases of the metal or components, and it is believed that the finer the grain, the greater will be the proportion of the amorphous phase. The exact correlation between grain-size and physical proper- ties is not clear, but grain-size measurements offer the advantage over other tests that they do not require elaborate preparation of the test specimen, and that they are made on the metal in the state in which it is to be used. That fine grain and high tensile strength and elastic limit go- together is generally conceded. The subject has been brought before the Faraday Society in a paper on “ Grain-Size Measurements in Metals and the Importance of such Information,” by Mr. Zay Jeffries. As a good example of increase of hardness AND TECHNOLOGY. with decreasing size of grain, Mr. Jeffries quoted some quite recent experiment of Fahrenwald, who prepared pure gold in four degrees of grain size, the extremely fine grain being secured by starting from colloidal gold; the hardness ranged from 94-7 down to 23-8, in Brinell numbers. Grain-size measurements can be made, generally on a polished and etched section, in various ways; if the number of grains per square unit be n, there will be grains per cubic unit. The author counts the number of grains within a circle which should be well within the field. If the circle encloses 66 com- plete grains, and cuts 28 grains, wThich partly lie outside the circle, then he finds that 66 + 28 X 0-6 = 82-8 grains is a fair average. The factor 0-6 was the mean of a great many determinations made on circles enclos- ing from 20 up to 290 complete grains; the factor actu- ally varied from 5-4 to 6-2, and if the boundary grain estimate should be wrong by 5 per cent., the total grain number would be wrong by 1 per cent, only, whilst the intercept and ITeyn methods gave much larger errors. He generally takes a circle of 79-8 mm. diameter, and gave, in his paper, a table, by the aid of which the number of grains per square millimetre could be read off for magnifications from 25 to 2,000 diameters. Measurements are made with a camera-microscope on screens (ground glass or paper) or photographs, the circle being drawn on a piece of tissue paper, attached to the screen; the circle should not enclose less than 50 grains. Some conclusions, it was said, could be drawn as to the cold work the metal has undergone, as stretching and compression would affect one direction in particular, Heyn’s method was recommended for this comparison. But thermal expansion by annealing complicated this interpretation, and grains and cells. should be distin- guished. Sir Robert Hadfield mentioned in this con- nection that he had counted, in a 0-58 carbon steel, the following number of grains per square inch : 5,540 as forged, 4,500 annealed, and 330,000 water quenched; with very fine grains, however, the microscopic deter- mination became almost impossible.—Engineering. Silica and Fireclay. In a paper on “ Silica and Fireclay Materials,” read before the Manchester District Institution of Gas Engi- neers, Mr. J. West mentioned that most silica bricks expand, wdiile ordinary fire goods contract, very materi- ally when subjected to high temperatures, and both these features are very objectionable. Most of the silica obtained from the pits in Derbyshire contains about 96 per cent, of silica. After many experiments, he succeeded in making an excellent and high refractory brick, which, in the experimental furnace, did not show any signs of expanding or contracting. These non- expanding silica bricks have been used in horizontal settings, with the results that the combustion chambers have practically retained their original shape under high temperatures, and retorts have remained true. The importance of these -features, especially with retorts operated by stoking machinery, will be appreciated. Even with suitable silica materials in combustion chambers retorts have sometimes sunk out of line, due to- the contraction of the fireclay material supporting the retorts. Silica segmental retorts with Glover-West settings had been in active operation for 1,165 days, and were still in excellent condition; and, apart from a pro- bable long life, there were advantages in the letting up and down of the retorts. They would stand higher temperatures; and, consequently, a larger output per retort was obtained. •Material containing about 85 per cent, of silica was . the most suitable for segmental horizontal retorts, on account of the small amount of expansion, and prefer- .™able to a material containing 95 per cent, of silica with 1gits higher expansion. In practice, it was found, taking Ha vertical retort bench as a whole, that there was a- total ^/expansion under working temperature of 2 in. in the scale test was carried out on a column of silica bricks 100 in. high, heated to 2,600 degs. Fahr., at which temperature the column was 100J in. in height. This expansion nearly coincided with that of the settings, and, being so little, was easily provided for. The author’s experience did not support the theory as to the higher percentages of silica, denoting higher refrac- toriness. On the contrary, one could get much better results with a smaller percentage of silica, when mixed previously with other suitable ingredients which improved the quality of the material, with the advantage that it was less liable to crack or crumble when cooled down. At the same time, the objectionable feature of expansiveness, which was so liable to disturb the settings, was. to< some extent eliminated. With regard to- the question of load and pressure on bricks when working at high temperatures in the settings, it had been found in many cases that, although some silica and fireclay bricks as tested in the laboratory gave very high refractory results, this did not indicate full proof of their remaining stable under load and at normal working temperature. Recent tests by Dr. Mellor had shown that high refractoriness was not a true criterion of the working value of bricks when tested with a load under heat. This was shown by the following table giving the temperatures which the materials could stand in a laboratory furnace before they fused, and those at which they gave way under load : Yielding Fusing Kind of material. temperature, temperature. Degs. Fahr. ~ ” China clay............... 2,570 Best fireclay bricks ..... 2,615 • .. Siliceous brick.......... 2,876 These tests proved the superiority of siliceous bricks for standing heavy loads in actual practice at high Fusing Degs. Fahr. 3,218 3,110 3,182 temperatures, and also showed that, with the best fire- clay goods, and the temperatures often employed, the danger zone was frequently approached. It was there- fore necessary that watch should be carefully kept over the practical working of retort settings when running at high temperatures, or there would be risk of collapse. The following data were quoted from the author’s tests on silica and fireclay materials from many sources : (1) (2) (3) Per cent. Per cent. Percent. Silica 93*20 .. . 91*60 . .. 89-27 Alumina 4-18 .. 6-32 . 8*53 Refractoriness ( 3,146° to i t 3,182° F. ' £ 3,146° F. . .. 3,074° F. Expansion per cent. when heated at 2,615° F... If Sample No. 2 was the brick that the author had been supplying for many years, and had an exceedingly low expansiveness; No. 1 was a brick he was supplying for war work under the Ministry of Munitions.; and No. 3 was a brick closely resembling those used for many years at Sheffield. These did not come up.to the Refractory Committee’s specification, and their success in actual use was important, as showing that a brick might stand up under loud even if its refractoriness was a little low.—Gas. COAL OUTPUT CONFERENCE. The question of increasing the output of coal was further considered on Thursday at a conference in London between the Parliamentary Committee of the Mining Association of Great Britain and the executive committee of the Miners’ Federation of Great Britain. The conference was held at the suggestion of the Home Office, and was a continuation of one held some weeks ago. It was officially reported at the close that the recommendation made at the last meeting for the appointment of local committees to deal with the ques- tion of absenteeism had been generally accepted, and committees had been formed. They had not been established sufficiently long, however, to justify any conclusions as to the result of their work, and the meet- ing was adjourned until a later date, when reports will be received after longer experience. The indications so far encourage the belief that satisfactory results will be obtained. COAL PRICES AND WAGES. Meeting on Thursday at the Westminster Palace Hotel, under the presidency of Mr. Robert Smillie, the Miners’ Federation of Great Britain had under consider- ation proposals which had been reported in the Press regarding the increase in the price of coal for home con- sumption. The committee held the view that there ought to be no increase in the selling price of coal to home consumers, and the officials were asked to draft and submit a resolution to an adjourned meeting of the executive. Mr. Smillie stated that a strong feeling pre- vailed that the Board of Trade should be approached directly by the miners, with a view to preventing further increases in coal prices. A joint Labour deputation waited on Mr. Lewis Harcourt, Acting-President of the Board of Trade, and Dr. Addison, Under-Secretary for Munitions, at the Board of Trade. The deputation, which consisted of the Parliamentary Committee of the Trades Union Con- gress, the executive of the Engineering and Shipbuilding Trades’ Federation, the National Labour Advisory Committee on War Output, and district representatives of the Federation, asked the Ministers to' lay before the Government a threefold request for the regulation of food and fuel prices, restoration of Board of Trade grants to societies paying unemployment benefit, and the taking of steps to compel trade unionists to pay contributions to their societies, and thus prevent them from utilising the Munitions Act to- evade their obligations. Mr. Harcourt drew .special attention to the “ vicious circle ” connecting wages advances and prices. He; pointed out that a rise in wages inevitably caused an increased cost of production in any trade, which was passed on to the purchaser. Even when Yvages advances were obtained by all, the general situation was not sub- stantially improved, as prices had svmpathetically increased all round. Dealing with the coal question, the right hon. gentleman pointed out the enormous demands being made by our Allies, and also emphasised the effect of the withdrawal of shipping for military and naval transport, and the obligation incumbent upon us of assisting our Allies and their people with the vessels at our disposal. New Transport Facilities in British Columbia.—A Bill has been introduced to appropriate 200,000 dots, for providing adequate transportation facilities in British Columbia in the shape of roads, trails, and bridges for such mineral properties as the development thereof warrants. Out of the above sum the Minister of Mines may authorise so much of the money as may be required by the Minister of Public Works for the construction of the needed roads and trails. The terms of the Act are as follows :—Whenever it is shown to the satisfac- tion of the Minister of Mines that development work on a mineral claim or group of mineral claims in any mining district has proved the existence of minerals or ore bodies in quantity and of commercial value sufficient to warrant an expenditure of public moneys for the construction of roads, trails, and bridges to facilitate the operation and develop- ment . of such mineral claiims, the Minister of Mines may authorise the expenditure of so much of the public moneys as may be required by the Minister of Public Works for the construction of such trails, roads, and bridges.