032 THE COLLIERY GUARDIAN. November 5, 1915. CURRENT SCIENCE The Bender Automatic Sprinkler. The automatic sprinkler invented by W. Bender, of Gelsenkirchen, has been tested at the Experimental Gallery, Derne, with the object of ascertaining, in the first place, the length of time elapsing between the starting of (the sprinkler and the firing of the shot. With a pressure of eight atmospheres in the water main, and the regulating tap turned half on, the shot was found to follow immediately, but on shutting the tap completely, the interval increased to a maximum of 12 seconds. The efficiency of the sprinkler in prevent- ing coal dust explosions was tested in the large gallery, the apparatus being set up so that the sprinkler was only 20 ft. away from the shot hole; and the tap being adjusted to give a 'retardation of 12 seconds to the shot. In these circumstances no dust explosion was produced by firing charges of 200 grammes of gelatine dynamite. Even with the tap adjusted so that the shot was only two-three seconds behind the sprinkler, the resulting coal dust explosion was prevented from extend- ing more than about 30 yds. along the gallery. This quenching effect, however, was not obtained in presence of firedamp on the side nearest the shot hole, the gas exploding, and the explosion being propagated beyond the sprinkler and through the gallery. Finally the sprinkler was set up about 50 yds. away from the shot hole, coal dust being strewn in the gallery, and a 9 per cent, firedamp mixture arranged in the explosion chamber. The resulting dust explosion was unaffected by the sprinkler, the latter being destroyed by the explosion. The conclusion drawn from these tests by Bergassessor Heise, reporting on behalf of the Westfalische Berggewerkschaftskasse, is that the Bender sprinkler, whilst unsuited for preventing the propagation of explo- sions, would be capable of preventing explosions due solely to coal dust, provided it were set up close in front of (the shot hole, and adjusted to allow the water to issue from the sprinkler for as long an interval as possible before the firing of the shot. On the other hand, it is ineffectual in presence of firedamp. Factor of Safety of Winding Ropes. Public hearings to consider mine safety rules were held in San Francisco on June 11 and 12, on the initia- tive of the Industrial Accident Commission and the United States Bureau of Mines. In the course of the discussion upon the phrasing of these rules, the mine managers present, says the Mining and Scientific Press, contributed a good deal of information of practical importance. The factor of safety in the strength of winding ropes provoked a long discussion. In the tentative rules the factor of 5 was adopted, but an increase to 8 was sug- gested. One veteran engineer said :—Increasing the factor of safety of ropes from 5 to 8 would involve a large expense. In many cases changing the factor of safety would mean changing the drums in order to put on larger ropes, and in the case of deep shafts it would increase the weight of the rope to such an extent that the capacity of the engine would be cut in two. Another manager said the hoisting drums in the Lake Superior country, where they have shafts 5,000 ft. deep, Could not possibly operate under a factor of safety of 8. The Red Jacket shaft, which is 4,900 ft. deep, handles about 17 tons dead load, that is, the weight of the rope and skip. It has 1J in. rope, with a breaking strain of about 100 tons. That is a fraction over the safety factor of 5. They have. had no accidents in their shafts due to the breakage of ropes there since the deep shafts have been put into use. There are four shafts deeper than 3,000 ft., three shafts over 4,000 ft., and two over 5,000 ft. At the Sacramento shaft of the Copper Queen mine, a net load of 13,0001b. is hoisted on a 4,4001b. rope made of l^in. crucible cast steel. This gives about 8| tons dead load; a IJin. rope has a breaking strain of 47 tons, so they are operating at a fraction over the safety factor of 5. Several experienced managers testified that they had been operating for long terms of years under the lower factor (5) without any breakage of the rope. Reference was made to Hans Behr’s paper on deep winding on the Rand, and he was quoted as saying that the factor of safety in force would limit operations to a vertical depth of 5,500 ft., because the weight of the cable would become unmanageable. In specifying for the new electric hoist to be erected at the Plymouth mine, a factor of 7 has been given. It was suggested that the time of service of the rope should be considered; that any rope is seldom in use for more than 18 months; and that if inspected carefully and frequently a factor of safety is introduced thereby. Nikola Tesla on the Future of Electricity. The well-known inventor, Nikola Tesla, has con- tributed to the Manufacturers Record his anticipations of the far-reaching applications of electric power. He states that with “ new, efficient, extremely cheap and simple thermo-dynamic transformers ” not less than 4,000,000 h.p. could be developed in electric generators by utilising the heat of blast furnace and coke oven gases. He expects confidently the practical realisation of this project in the very near future, and looks to exceptionally rapid electrical development in this direc- tion. “ But the time is very near,” he adds, “ when we shall have the precipitation of the moisture of the atmosphere under complete control, and then it will be possible to draw unlimited quantities of water from the oceans, develop any desired amount of energy, and com- pletely transform the globe by irrigation and intensive farming.” The present limitations in the transmission of power to distance will be overcome in two ways— through the adoption of underground conductors insu- lated by power, and through the introduction of the AND TECHNOLOGY. wireless art. The inventor has many wonders in view, but of the three main sources of life-sustaining energy— fuel, water power, and the heat of the sun’s rays—he considers the second to be by far the most valuable resource, and on this, he thinks, humanity must build its hopes for the future. Units from Refuse. One of the effects of the rise in coal prices has been to direct greater attention to the generation of power from refuse and other waste products. Writing in the Electrical Review, John B. Morgan gives his experience at the Horsham electricity works. The working of the destructor at these works has been carefully recorded— during the 12 months ended with March, 1,421-80 tons of refuse were burnt, and 107,690 units generated, giving an average of 76-1 units per ton; but during January an average of 105-5 units per ton was secured. The destructor steams at the day load only, but, as experi- ment, the day load was worked on coal, and the refuse used on the evening load; the result was a figure of 120 units per ton. The refuse was of poor quality, but Mr. Morgan thinks that with refuse of fair quality and turbo-driven generators, the yield should be easily raised to 200 units per ton. In the period referred to, it is estimated that coal to the value of J-320 was saved, and there was an income of .£68 from by-products, the net profit working out at £127. This is a case, of course, in which coal is relatively dear. In a recent report, Dr. Whitehouse, the medical officer of health for Deptford, gives some useful facts and figures^on the fuel value of town refuse which are of particular interest at the present time, when economy is being called for all round. He states, in the course of his report, that the composition of ashbin refuse varies considerably, but quotes the subjoined as a repre- sentative example of what is obtained in towns :— Weight per cent. Breeze and cinder .................... 50’0 Paper, straw, fibrous and vegetable refuse 13’0 Coal.................................. 0’7 Bones and offal ....................... 0*6 Rags................................... 0'4 Coke................................... 0’3 Ash ................................. 12’0 Dust and dirt ........................ 20’0 Bottles, 1 per cent.; tins, 0’7 per cent.; metals, 0’2 per cent.; crockery, 0’6 per cent.; broken glass, 0’5 per cent.... 3’0 100’0 The quantity of ashbin refuse produced varies very largely in different districts. It usually ranges from about 4 cwt. to 7 cwt. per head per annum. A table is given showing that the average calorific power of 1 lb. of ordinary ashbin refuse, when dry, is 3,696 units of heat, and if fully utilised would evaporate 3-826 lb. of water from and at 212 degs. Fahr. :— Ca'orific power, or units of heat per pound of the combustible Evaporative power of— r When dry. When con- taining the average amount of moisture. Coal 14,000 9,334 Coke 12,000 8,000 Bones and offal 8,000 5,334 Breeze and cinder 6,000 4,000 Rags Paper, straw, fibrous material, & vegetable 5,000 3,334 refuse 3,800 2,534 The quality of refuse from a combustion point of view naturally varies very much, but the methods of dealing with it have much in common, combustion being assisted by hot air delivered into the furnace ashpit. The furnace is of ordinary construction, having movable firebars. Fram 1-8 lb. to 2 lb. of water are usually evaporated from and at 212 degs. Fahr, per lb. of refuse, and about 501b. to 701b. of refuse are consumed per square foot of grate area per hour. Circuit Breakers. In a paper read recently by K. C. Randall, before the American Institute of Electrical Engineers, some remarks were made on arc phenomena and recent tendencies in the design of circuit breakers. In an ideal oil breaker the current will not continue after the first zero value following the first complete separation of contacts, but in practice, especially on large powers, the current generally continues owing to one or other of the following causes :—(1) Insufficient separation of the contacts; (2) large amount of gas formed in the arc; (3) reduction in insulating value of oil between the con- tacts caused by suspended metal and carbon particles condensed after each successive half-circle arc in an alternating current. Oil, being the accepted insulating medium, should be of high grade, especially on the higher potentials. Oils of low volatilisation, slow car- bonisation, and fair insulating value are desirable. In low temperatures, non-freezing oil should be used, but as these are usually very volatile at ordinary summer temperature, another, oil should then be used. A large volume of oil, with a considerable head over the contacts is desirable for various reasons here specified. As regards length of break, it is found that the separation should only be enough to prevent puncture of the inter- vening oil at the available potential. A number of breaks in series is usually preferable to the common two-break construction, although a multi-gap breaker involves difficulties in design. As regards self-induction, the total effect in high frequencj^ circuits will usually be less than with lower frequencies. Facility of de-ionisation of the arc gases will depend on the tempera- ture and pressure of the surrounding oil, on the shape and volume of contacts, and on their heat conductivity and vaporising temperature. Large contacts of smooth shape are therefore desirable. Rapidity of opening and closing contacts is desirable, and gravity-actuated breakers need an accelerating device. Modern practice favours the solenoid operation for all remote-controlled oil breakers. Since enormous energy must be dissipated in breaking large currents, breakers for such circuits must be constructed to withstand a violent shock. Reactance breakers are now constructed on improved methods, amongst which the shunted breaker deserves attention. Among the notable mechanical features found in modern breakers are : (1) Increased strength of tanks with supports and fittings so as safely to with- stand the shock of rupturing large powers; (2) rapid acceleration of breaker so as to obtain high rates of contact separation with the attendant early termination of arcs, and consequent reduced energy dissipation; (3) provision for vented expulsion chamber over the oil from which gases may escape without entraining much oil, thus reducing the high and otherwise destructive pressures occurring in heavy duty; (4) arrangement for liberal and easily replaceable contact parts of minimum cost, in even small as well as large capacities; (5) employment of large capacity, (jingle) pole units, suit- ably assembled, and operated from a single separate mechanism, instead of using multi-polar units assembled with individual mechanisms. 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 :— Coal Syndicate Report for September. Total coal raised, 6,331,704 tons (5,509,528 tons in September 1914), or 243,527 tons (211,905 tons) per working day. Calculated distribution, 5,055,403 tons (4,121,149 tons), being 194,439 tons (158,506 tons) per working day, or 66-20 per cent. (54-00 per cent.) of the participation. Total coal distribution of the syndicated collieries, 6,457,752 tons (5,355,003 tons), or 248,357 tons (205,962 tons) per working day. Deliveries, including local sales, miners’ house coal and supplies to pits’ own ironworks : Coal, 3,572,726 tons (3,522,416 tons), or 137,413 tons (135,478 tons) per working day; coke, 1,630,525 tons (871,060 tons), or 54,351 tons (29,035 tons) per working day; briquettes, 335,903 tons (249,171 tons), or 12,919 tons (9,548 tons) per working day. The collieries having a sales agreement with the Syndicate produced 454,279 tons (361,407 tons) of coal, and dis- tributed 411,024 tons (340,857 tons), of which 180,854 tons (140,455 tons) were for Syndicate account. Their total distribution of coke amounted to 114,810 tons (105,808 tons), of which 75,597 tons (61,922 tons) were for Syndicate account; and the distribution of briquettes totalled only 2,497 tons, all for Syndicate account. Acquisition of Mining Properties. The Vereinigungsgesellschaft Rheinischer Braun- kohlenbergwerke, G.m.b.H., Cologne, has acquired 2,199,243 sq. metres in the district of Geilenkirchen, for the purpose of raising brown coal. Rhine Shipping. Owing to the falling river, boats drawing more than 6 ft. of water have been unable to get up as far as Strassburg, and the loading of large craft has had to be considerably lightened in consequence. The delays resulting from this cause, fog, and slow unloading at up-river ports, have caused a scarcity of accommodation for freight, and rates have again advanced. At the same time, part of the daily deliveries at Ruhr ports from Westphalian collieries has had to be left on the quay. Stocks on the Upper Rhine are large, and there is therefore no fear of a scarcity, apart from the fact that it will still be possible to ship for several weeks. German Commerce After the War. A meeting of the Central Union of German Merchants and of the Federation of Merchants took place recently for the discussion of the tasks confronting the foreign trade department formed by the War Committee of German Trade. That German manufacturers and mer- chants are very keen in this preparation for after the war period may be gathered from the fact that an extra- ordinary number were present at the meeting. Prof. Dr. Bernhard Hanus, of the Society for the Promotion of the Institutes of Maritime Traffic and World Com- merce, gave a lecture on the necessity for a careful cultivation of German foreign trade after the war, and pointed out that even during the war it would be wise to take steps therefor. One thing necessary for this pur- pose was a systematic investigation of the world’s com- mercial conditions. Both practice and science must render their service in this matter. Modern commer- cial science excluded all political aims. An animated discussion followed, and a resolution was passed approving the preparatory steps taken towards the furtherance of German commerce in the domain of foreign trade. The meeting considered the further development in this direction to be urgent, and stated their intention of entering into communication with other associations, requesting them to co-operate. Company Reports. Harpcner Bcrgbav A.G., Dortmund. — The annual report states that the coal production for the past \Va.r amounted to 6,454,559 tons (8,206,664 tons), 1,170,422 tons (1,366,241 tons) of coke, and 443,989 tons (453,643 tons) of briquettes being also produced. The total gross profit was 21,223,068 mk. (28,361,177 mk.), and the net profit, after writing off 7.868,154 mk. (7,509,635 mk.), was 7,721,845 mk. (9,500,334 mk.). Out of this sum, 5,100,000 mk. (6,800,000 mk.) have been allotted