December 24, 1915. THE COLLIERY GUARDIAN 1290 CURRENT SCIENCE AND TECHNOLOGY. Data on Belt Conveyors. The following condensed formulae and data on belt conveyors have been prepared by E. H. Messiter (Mining and Engineering World). The normal load for a 20 in. troughed belt conveyor is 20-100 of 1 cu. ft. per foot of belt. For other widths the normal load is proportional to the square of the width. The normal capacity of a 20 in. troughed belt running 100 ft. per minute, material weighing 1001b., per cu. ft., is 1 ton per minute. For other cases capacity is proportional to weight of material, speed, and square of width. The width of conveyor required is often determined by the size of the material rather than the capacity. For material of uniform size, multiply the size of the material in inches by 3 and add 6 to obtain the proper width of conveyor in inches. (Consider the lumps as cubes, and take a side of the cube as the size of the material.) For unsized material multiply the size of the largest lumps by 2 and add 8 to obtain proper width of conveyor in inches. To find approximate horse-power received per 100 ft. length of conveyor for any size horizontal troughed belt with normal load : For ore, divide tons per hour by 60; for coal, divide tons per hour by 45. Additional horse- power for elevating : Multiply tons per hour by height in feet, and divide by 1,000. Correct within 1 per cent, for any conveyor, elevator, or hoist. The following table gives the belt tension per horse- power that will just permit slipping on drive pulley when coefficient of friction is 0-25 :— Arc of Contact. 180 degs. 250 degs. 270 degs. #360degs. Speed. (----A---(-------A---t--------A--i--------*-- aba b a b a b 100 ... 606 ... 276 ... 530 ... 200 ... 477 ... U7 ... 417 ... 87 200 ... 303 ... 13S ... 265 ... 100 ... 239 ... 74 ... 209 ... 44 300 .. 202 ... 92 ... 176 ... 67 ... 159 ... 49 ... 139 ... 29 400 ... 152 ... 69 ... 132 ... 50 ... 119 ... 37 ... 104 ... 22 a Lb. tension on tight side. b Lb. tension on slack side * Tandem drive. To obtain actual tension, multiply figure in table by the horse-power. On vertical curves the radius of curvature such that the belt will just lift off the idlers is equal to the belt tension in pounds, divided by the weight of the belt per foot, plus the height from lowest to highest point of curve. Use of Pulverised Coal in Metallurgical Furnaces. Prof. C. H. Fulton stages that in using pulverised coal for firing the reverberatory furnaces of the Canada Copper Company the coal is ground to 200 mesh, and was originally fired 'through five, nozzles into which it was conducted by screws. The first furnace was 12 ft. long by 19 ft. wide, with extreme inside height of 6 ft. The bottom was an inverted arch of magnesite brick. Grate-fired reverb oratories were found not adapted to the new practice. The roof required frequent repairs owing to the excessive heat. The magnesite bottom was replaced with silica, and the roof raised to give a com- bustion space of 6 fa. Bin. high above the skimming line. The manner of charging was changed, the ore being introduced along the sides of the furnace, and the change resulted in an increased ratio of charge to fuel. During the first three months of 1914 the monthly average of tons of charge smelted per ton of fuel was respectively 5’0, 5*65, and 6’77. E. P. Mathewson, in describing the Anaconda practice, states two points are essential for the success of coal dust firing The coal must be dry, containing less than 1 per cent, moisture before pulverisation, and the grinding must be carried to a very fine point. Pro- bably 95 per cent, should pass a 100 mesh screen, and 75 per cent, through 200 mesh. The flame is as easy to handle as gas. About 50 per cent, of the ash is absorbed by the charge, and the balance caught in the flue connection to the waste-heat boiler. With the use of coal dust firing and side-wall charging, it is no longer necessary to stop the furnace for fettling, and in .the larger furnaces the flow of slag can be continuous as in copper blast furnaces. — Mining, Engineering,'and Electrical Record. Corrosion of Steel Smoke Stacks. The discovery that a number of steel smoke stacks throughout the country are corroding at an alarming rate has aroused much interest among central station com- panies, insurance interests, and others. A superficial inspection of the exterior of many of these stacks indicates that they are apparently in a satisfactory con- dition, but when scrutinised on the inside, it is found that disintegration in many cases is proceeding rapidly. Of the stacks examined a few were lined, and these were free from attack. Those without any lining whatever were, however, deteriorating in practically every case. A steel stack will corrode on the inside and on the outside, but this fact appears to have been overlooked in many instances, for protection has been given the exterior, while the interior has been ignored; although internal corrosion is by far the more serious of the two. Corrosion of the outside of a stack is due in part to the elements and in part to acids and sulphur fumes, which attack steel quite rapidly in the present of moisture. According to R. I. Elkin (Electrical World), an inexpen- sive way to prevent corrosion is to paint the steel with a suitable pigment. The conditions affecting a smoke- stack are similar to, but much more severe than, those existing round other steel work, bridges, etc., on account of the atmospheric conditions and the rather high tem- peratures—a combination most favourable to corrosive action. The painting should be thorough, and not less than two coats should be applied, otherwise the pinhole abrasions in the paint, and uneven coating, may give a covering which is not completely protecting. To obtain the benefits of painting, it should be done regularly, the frequency depending upon local conditions. About every two years suffices in average cases. It is a less simple matter to prevent corrosion in the interior of a stack, and one which will cost more than outside protection, because the hot flue gases direct from the fires must be contended against. These gases are extremely corrosive, and will cause rapid disintegration of the steel if preventive means are not taken. The corrosion is due almost wholly to the flue gases contain- ing moisture, which condenses against the comparatively cool walls of the metal stack. 'The condensate thus pre- cipitated consists largely of sulphurous acid, while there are always present the deleterious effects of carbon- dioxide gas, which attacks steel in the presence of moisture. The remedy for corrosion on the interior of a stack is to protect the metallic wall from the acids and gases by lining it with firebrick. This lining should be carefully laid, care being taken that no air gap exists between the lining and the metallic wall, otherwise the corrosion will take place as fast as, if not faster than, when no lining is used. The intervening space between metal and brick should be filled in completely by grouting with cement. The lining should go the full height of the stack, because with unlined stacks it has been found that the upper rings corrode faster than the lower, owing, no doubt, to the greater condensation at the top of the stack. One of the things most conducive to corrosion is to take an unlined stack out of service from time to time, even for short periods. Experience, however, seems io indicate that allowing a stack which is properly lined to stand idle has little effect upon corrosion. This is a great advantage to steam plants operating in connection with hydro-electric plants where the water supply is erratic or insufficient at all periods of the year. A further advantage of lining a stack, besides that of pro- tecting it and thereby prolonging its life, is that the radiating losses through the metallic walls are very materially reduced, thus improving the draught. Salt as a Coal Saver. Prof. E. A. Sonnenschein, in a letter to the Times, described the good results he had obtained in the domestic use of coal through sprinkling a hundredweight of cheap slack with a solution of a tablespoonful of salt- in a little less than a pint of water. It is difficult to account for the results achieved through the medium of about one part of a non-combustible and non-sup- porter of combustion with some two thousand parts of coal, and Prof. Sonnenschein said :—“ I would also not exclude the possibility of a psychological process at work.” Some explanation of the beneficent effect of this salt treatment has been put forward by Dr. A. Vernon Harcourt, also in a letter to the Times. Dr. Harcourt says that the deliquescent property of the salt particles distributed on the slack serves to bind the small particles together, “so that a handful becomes a piece of coke, which burns -with a steady glow, like the coke which lumps of coal, after giving off their gases, leave behind them.” The improved combustion which Prof. Sonnenschein claimed may therefore arise from the better access of air in the absence of very small coal and dust, which frequently cause bad smoking in boiler practice from the choking of air passages through the fuel and the grate bars, but the “ psychological process ” must not be entirely overlooked. 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 Market in South Germany. Although the demand for coal has diminished to some extent of late, the scarcity of fuel has not decreased. This is due to the shortage of railway wagons, and also to the reduced output in the Ruhr and Saar districts. For the latter reason, too, waterborne consignments have been restricted, though the river was in favourable condition for traffic. On the other hand, shipments direct from collieries on the Rhine and Rhine- Herne canal improved. The arrivals at up-river ports were, nevertheless, insufficient to meet the needs of the regular trade. Whilst extending to all kinds of fuel, the scarcity has been most apparent in small nuts, which are the favourite fuel of many large industrial consumers, consequently, other grades have had to be substituted. The variety for selection, however, is not large, and the local briquette works cannot be drawn upon to any great extent, being already full up with orders to the extent of their lessened output capacity. The result is that deliveries are getting more and more in arrear, and the difficulties of consumers, with regard to the maintenance of an adequate supply of fuel to keep their works going, are increasing. The position of the house coal trade is less acute owing to the continued mildness of the weather; but even here, the supply is much below the demand, and substitution has to be extensively practised. The scarcity of anthracite continues, though the supply has improved since the Swiss market has been fed by Belgian anthracite, leaving the Ruhr anthracite avail- able. In coke, there is little difficulty in meeting the demand for broken I. and II., though III. is still scarce. Owing to the prohibition on the export of broken coke, Switzerland has to be content with large, which is broken locally. Brown coal briquettes are in such great request that delays are frequent, and all stocks have been exhausted. The question of renewing coal contracts is shortly coming on, and care will be exercised in the apportionment of the various qualities, and in limiting the sales, as far as possible, to the old level. There being no competition, it is not expected that much busi- ness will change hands; and there is little possibility that the growing tendency on the part of Saar coal users to change to Ruhr coal will be satisfied. German Steel Output in November. The preliminary report of the Steel Works Union gives the deliveries of semi-manufactured steel as 63,000 tons (68,344 tons in October), railway superstructural material 116,000 tons (130,981 tons), and sections 54,000 tons (57,953 tons)—total 239,000 tons (257,278 tons), calculated as raw steel. German Coal Syndicate. The coal owners’ levy for Ocober has been fixed at 6 per cent, for coal, 3 per cent, for coke, and 4 per cent, for briquettes. The production of coal, coke, and briquettes for December has been left at the old level of 80 per cent, of the participation. The Brown Coal Market in Mid-Germany During November. The Brown Coal Association, of Halle, reports that the demand for brown coal in November was good throughout, being in part higher than in the previous month and in the corresponding period of 1914. The reduced business experienced in some cases was due to the scarcity of labour and, above all, of coal wagons, the deficit in the latter being so great as to lead to short time at many of the mines, and to the stocking of briquettes. There has been an increase in the employ- ment of female labour and of men from outside sources. Company Reports. Miilheimer Bergwerks-Verein, Millheim.—The trading profit for the second quarter amounted to 572,925 mk. (498,586 mk. in 1914), making 1,197,615 mk. (1,103,938 mk.) for the half-year. Gewerkschaft Friedrich der Grosse, Herne.—During the second quarter a surplus of 552,126 mk. (608,771 mk. in 1914), of which 97,603 mk. (nil) has been set aside for extinction of loans, and 387,123 mk. (113,419 mk.) for new plant, 149,250 mk. (298,500 mk.) being distri- buted, and 30,855 mk. (20,201 mk.) retained in hand. Bo chum er Verein fiir Bergbau und Gussstahlfabrika- tion. — Out of the gross profit of 11-9 million mk. 9,803,953 mk.), 4*5 million mk. (5,443,810 mk.) have been written off, leaving 7-4 million mk. (4,360,143 mk.), out of which 1-5 million mk. are to be placed to the staff war fund, and a dividend of 14 per cent. (10 per cent.) is to be paid. Gewerkschaft Lucherberg, Duren.—Total coal raised, 313,486mk. (331,277 mk.j, briquettes manufactured, 79.700 mk. (84,885 mk.). After writing off 133,760 mk. (91,284 mk.), there was a loss of 220,422 mk. Oberschlesische Eisen-Industrie A.G. fiir Berg- und Hilttenbetrieb, Gleiwitz.—Including a forward balance of 723,024 mk. (213,905 mk.), a gross profit of 5,092,972 mk. (4,800,057 mk.) was obtained, the net profit being 962,196 mk. (785,024 mk.), of which 840,000 mk. are -to be distributed as a 3 per cent, dividend, and 55,196 mk. (723,042 mk.) carried forward. Briixer Kohlenbergbaugesellschaft.—Trading surplus, 7,170,505 kr. (8,592,812 kr.); receipts from interest, 786.700 kr. (755,996 kr.); rents and crops, 193,949 kr. (185,545 kr.); taxes, 2,050,133 kr. (1,678,962 kr.); depre- ciation 2,000,000 kr. (2,100,000 kr.); sundry outgoings, 21,760 kr. (21,760 kr.); net profits (including forward balance, 1,934,030 kr.), 6,013,299 kr. (7,649,262 kr.); dividend, 25 per cent. (25 per cent.); carried forward, 1,537,805 kr. The coal production fell to 3*4 million tons, a deficit of 470,000 tons. Gewerkschaft des Steinkohlen-Bergwerks Langen- brahm, Riittenscheid.—Out of a total profit of 2,591,695 mk. (3,537,998 mk.), 607,800 mk. (702,131 mk.) have been devoted to writing off; 345,821 mk. (378,690 mk.) to cover extraordinary expenditure; 150,000 mk. (200,000mk.) to provision for subsidence damage; and 250,000 mk. (1,800,000 mk.) distributed among the shareholders. After placing 700,000 mk. (nil) to capital account, 88,073 mk. (307,177 mk.) are carried forward. During the first quarter of -the present year, 125,485 tons of coal were raised (179,755 tons the previous quarter, and 131,804 tons in the first quarter of 1914), on which a profit of 394,697 mk. (490,088 mk. and 718,134 mk. respectively) was obtained. Gewerkschaft Pfannenberger Einigkeit, Neunkirchen. —Total iron ore raised during the year, 159,758 -tons (185,705 tons). A profit of 683,524 mk. was made, of which 500,000 mk. wTere distributed, the remainder being devoted -to new plant and reserve. Gewerkschaft Storch und Schoneberg, Kirchen.—Total iron ore raised, 213,571 tons (278,925 tons); deliveries, 181,866 tons (239,311 tons). Profits distributed, 280,800 mk. (374,400 mk.) and 523,252 mk. (602,932 mk.) written off. Zeche Heinrich, Ueberrunr.—Coal raised during the second quarter, 47,661 tons (53,031 tons); surplus, 274,654 mk. (166,235 mk.); dividend, 150,000 mk. (125,000 mk.); carried forward, 511,840 mk. (390,982 mk.). Eisenwerk Laufach, A.G. — The trading profit fell from 242,199 m. to 149,956 mk., and after deducting 133,336 mk. for general expenses, interest, etc., and writing off 39,037mk., there remained a loss of 22,416 mk., which has been wiped out by means of the forward balance and drawing 615 mk. from special reserve. Last year a 4 per cent, dividend was paid. Gewerkschaft des Steinkohlenbergwerks Kulmitz, Waldenburg. — Gross profits, 894,820 mk. (1,108,993 mk.), of which 252,540 mk. (336,154 mk.), have been written off, 331,875 mk. (337,500 mk.) paid in debenture interest, and 27,603 mk. set aside for war expenses, leaving net 124,242 mk. (340,575 mk.). Dividend, 100,000 mk. (270,000 mk.); reserve, 10,000 mk. (40,000 mk.); carried forward, 14,242 mk. (30,575 mk.).