1224 THE COLLIERY GUARDIAN, June 11, 1915. never been anything more than local explosions in the Pennsylvania anthracite district, which now produces over 80 million tons per annum, although there have been a great many ignitions and local violent explosions of firedamp; indeed, that district is one of the most gaseous in the world. There are a number of collieries giving oft over 3,000 cu. ft. of pure methane per minute. In the experimental mine no ignition was obtained of Pennsylvania anthracite, in which the ratio of volatile combustible to fixed carbon is less than 7 to 93, even when a considerable percentage of firedamp was present; but there is a certain kind of coal in one of the anthracite basins in which the ratio of volatile matter to fixed carbon is about 10 to 90; and, while the dust of this coal without firedamp present would not explode, when 1 per cent, of natural gas was put into 1,300 g. 1,200 1,100 -1,000 50 BARRIER 4300 Fig. 7 —Curves of Test No. 46. 3-io ^Z500 >‘a ^-400 a: 1100 800 Fig. 8.—Curves of Test No. 86. the atmosphere a light explosion occurred. With 3-2 per cent, of firedamp in the air an explosion was propa- gated through this semi-anthracitic dust, even when 30 per cent, of shale dust was in the mixture. Subse- quently, it was decided to conduct a series of com- parative tests on typical coals with different mixtures of shale and different percentages of firedamp. This series has been barely started. In order to systematise the work, certain empiric methods of ignition and propa- gation were necessarily adopted. Character of Shale Dust Used in Testing. In the earlier testing at the experimental mine, the roof shale was ground up to provide an inert dust, but it contains from 8 to 10 per cent, of combustible matter, and the latter was found to affect the results to some extent, although less than would an equivalent per- centage of Pittsburg coal dust. Accordingly, a shale below the Pittsburg bed was opened, which contains less than 1 per cent, of combustible matter, and this is found very satisfactory as an inert or non-combustible dust. Limestone dust has been tried for zonal treatment and in barriers; it seems to be excellent for stone- dusting, as it gives a white appearance like whitewash, and sticks well both to the roof and to the walls. Under the Bureau’s direction, it is being employed in a com- mercial mine in the Pittsburg district. Limiting Curves for Explosibility of Coal Dust Mixtures. The investigation of explosibility limits of various kinds of dusts and dust mixtures has only been started in the experimental mine work, but it has gone on far enough to indicate some very important features. These are strikingly brought out by some limiting curves, which are presented as merely preliminary, and subject to change. Confirming the earlier small gallery and laboratory tests of Mr. Taffanel and others, the results of the experimental mine testing show that the ratio of vola- tile combustible matter to total combustible matter has great influence in the question of relative explosibility. The importance of the inert material, moisture, as of coal,' and other inert matter, such as shale, sand, or clay, has long been apparent. It was thought that if these factors were used as ordinates and co-ordinates, they would give curves which would be of •: value in defining the limits of explosibility. Accordingly, the limiting curves shown in fig. 6 were drawn. It must be understood, however, that these are subject to very material correction as the work proceeds. The better- defined curves are of ignition without gas, and propaga- tion without gas. The gas or firedamp curves require many more limiting points from tests before they can be correctly drawn. It is, of course, the intention to make tests of coals in which the volatile combustible ratio lies between those already tested, and at the time of writing tests are just being begun on coal in which the volatile combustible to total combustible ratio is 30 to 100. Many of the points on the ignition and propagation curves without gas of the coal shown have been repeated, and, in some instances, several times, so as to ensure accuracy. It will be observed that with ignition from the cannori without gas the Pittsburg dust will not ignite when the percentage of shale is 60 per cent, (giving a total non-combustible matter proportion in the mixture of 62 per cent.). With the Beckley seam coal there is non-ignition with 40 per cent, of shale dust in the mixture;. and the semi-anthracite tested will not ignite even if pure—that is, without mixture of any inert dust. When, however, 1 per cent, of gas is introduced into the air current, the non-ignition limit of Pittsburg dust is raised to 70 per cent.; of the Beckley dust to 50 per cent.; of the Kittaning dust to 40; and the pure semi- anthracitic dust will just ignite. When 2 per cent, of gas is used in ignition tests, the upper limit for Pittsburg dust has not been determined; with the Beckley coal it is found that with 2-3 per cent, of gas a 60-per cent, mixture will ignite; but when there is 70 per cent, of shale, it will not ignite. In the propagation test, the Pittsburg coal dust in a mixture with 70 per cent, of shale will ignite; with 75 per cent, it will not ignite. The Beckley dust will -■ - 1,2OO - - 1,000 * —300 0-400 I300f- -800 -900 700 600 -200 100 ■E150 -E50 -E650 ■E1,05C : 1,1 IK §5 30 0*8 .30 TIME, IN SECONDS '6 950 - T63 E750 ZE315U- >■2 0-4 1-0 1-8 54 “2 -S“i ulg! 5“ 5? cl < w “glO < w Fio Z 50C Bs Fig. 9.—Curves of Test No. 94. not ignite with 50 per cent, of shale, and the same is true of the lower Kittaning coal. There have been a number of . propagation tests with gas, which show that the limit is very much raised. For example, with 3 per cent, of natural gas, there was propagation with the Pittsburg dust with 80 per cent, of shale mixture; and, at the other end of the scale, with the semi-anthracite there was propaga- tion as high'as 30 per cent, of shale dust mixture. What lias long been conjectured is therefore manifest— namely, that firedamp is most influential in increasing the danger of occurrence of widespread coal dust explo- sions. Rock Dust or Stone Dust Barriers. The first barriers used at the experimental mine were the so-called “ Taffanel shale dust barriers,’’ con- sisting of 10 ’ shelves, and, as later recommended, 15 shelves, to launch suddenly into the air through the agency of the pioneering wave a dense cloud of shale dust. These plain shelf barriers proved very effective in the experimental mine tests in almost all cases, except in very light; explosions, which were, in fact, mere inflammations, not accompanied by enough pres- sure to displace sufficient shale dust for extinguishing the flame, as was. the case in 'the Clarence Colliery explosion (France). The open shelves for dust are not generally so well suited for American mining conditions. Accordingly, the writer designed a number of easily operated barriers, enclosed for the protection of the dust, and planned for different situations and conditions. The effect of launching a large amount of shale dust into the air is strikingly shown by the diagram (fig. 7) of explosion tests No. 46, which, while very slow in starting, became a very violent explosion, .causing a pressure of 119 lb. at station 750; but a Taffanel barrier 50 ft. outbye extinguished it, and at the next station, 400 ft. beyond, at which there was a manometer, the pressure was but 12 lb. The use of barriers has been of the utmost value in testing work, and has permitted of explosions being con- ducted along a predetermined irregular path. Stone Dust Zones. A considerable number of experiments have been made to determine the length of the zones of shale dust and of limestone dust necessary for extinguishing strong explosions, such as is given by 300 ft. of pure coal dust. This distance of 300 ft. is selected, because it is the ordinary maximum length of a room or working place, and it is thought that such a working place might not be well rock-dusted. The curves of test 86, shown in fig. 8, are of an explo- sion which was stopped by a shale dust zone in a dis- tance of 250 ft. to 300 ft. The curves of test 94 (fig. 9) show the more gradual dying away of the explosion in a mixture of 20 per cent, of coal dust and 80 per cent, of shale. The mixing of the coal dust was to make the conditions parallel to those which would be found in ordinary mines. In this case, the explosion travelled 700 ft. in the mixture. The test indicates the importance of preventing an explosion from starting; and on this account, where rock-dusting is employed, zonal treatment would not be satisfactory, but the dusting should go throughout the mine, and as close to the working faces as practicable. THE GERMAN AND AUSTRIAN COAL AND IRON TRADES. We give below further extracts from German periodicals that have reached us, showing the course of the coal and iron trades in Germany and Austria :— Rhenish Brown Coal Briquette Syndicate. The Brown Coal Briquette Sales Association has been converted into a syndicate (Rhenishes Braunkohlen- brikett-Syndikat G.m.b.H., Cologne and Mannheim), with a capital of 2,000,000mk. (25 per cent, paid up). The membership comprises 25 briquette works, with a total output of 8-01 million tons per annum, which is not to be increased for three years, but provision is made for granting supplementary allotments in the event of an increased demand in the interim. The Iron Market in Rhenish Westphalia. The advance in the price of all rolling mill products continues, the works being fully occupied, within the limits of their restricted producing capacity, and being obliged to require longer time to give delivery. Conse- quently the various convention prices are not only maintained, but considerably exceeded throughout. For instance, the basis price for bars, which was fixed at 135 mk. per ton by the convention, ranges between 140 and 150 mk., an additional charge of 1’5-20 mk. being made .for high-grade material, such as open hearth steel, owing to the short supply. In fact,, business in bars is chiefly restricted to high-grade material, which is practically the only kind used for war supplies, whilst comparatively little is being done in ordinary commer- cial bars. The conditions in the plate market are very similar, the convention basis price of 140-145 mk. for heavy plate being mostly exceeded by several marks per ton; and 170-175 mk. are obtained for fine plate. On the other hand, the works are adhering to the conven- tion rates for tubes, in spite of the small demand; and the Mannesmann Works have booked Orders for weldless tubes at 10 per cent, above the Convention price. The demand for wire is so heavy that the works can hardly satisfy it, and, consequently, in this branch also, the convention prices are exceeded for the most part. Crude rolled wire, for instance, is unobtainable now at the convention price of 135 mk., the actual rates asked being 140-147|mk. Wire goods and drawn wire are likewise in very active request, and consumers who require prompt delivery have to pay high prices. Every- thing points to still further advances all round, and the cessation of- exports to Italy — which had latterly attained considerable proportions—will have practically no influence on the market, in view of the general scarcity of material, and the'impossibility of appreciably increasing the output. - . . The German Potash Industry. A.report in the Cologne Gazette states that, consider- ing the situation produced by the war and the prohibition of exports, the quantity of potash products distributed up. to the present may still be regarded as satisfactory, though, on; the other hand, the cost of production has risen considerably. through the diminished output,