June 8, 1917. THE COLLIERY GUARDIAN. 1081 value to read a little high. Firedamp should therefore be looked for first, and estimated. Then, the oxygen value having been determined, it is corrected by subtracting one-fifth of the firedamp percentage. For example, if there is 2'5 per cent, of firedamp present and oxygen reads 20 per cent., the corrected oxygen proportion is 20 — 0’5, or 19'5 per cent. The lamp has a round wick and burns benzoline. No other fuel should be used. Provided that the lamp is kept clean and in good general condition, and is used with reasonable care, it has been found that, on the average, the error in determining oxygen does not exceed | per cent. The makers have arranged that every , lamp passes through Dr. Briggs’ hands before being sent out, every one being calibrated independently at the Heriot-Watt GRADE REVISION FOR UNDERGROUND HAULAGE* By R. D. Brown. Economic location of underground roadways means a location which will result in the production of a maxi- mum tonnage with the minimum expense when the mine is operating to capacity. To attain this standard, it is presupposed that records of drillings and relative data have been used by the promoters of the enterprise in adopting the original working plan which at that time seemed most suitable to the known natural conditions. As development reveals the existence of irregularities, it becomes necessary to revise the original plans in order to obtain a practical solution of the problem. In many mines the coal lies practically horizontal, and grading is unnecessary; in others, the construction of a permanent road bed requires considerable expense for revision, due to the irregularity of the undulating bed. If development is carried out according to a practical definite plan, the main line roads will be so constructed i that the general grade, either with the loads or against them, will not be excessive. It must be remembered that the loaded cars all travel in one direction, and that the capability of the motor to handle the load is a limiting factor. Thus, a ruling grade may be either with or against the loaded trip, depending on the capacity of the motor when pulling or the braking control when descending a grade. When the average grade is excessive, a locomotive depending on the adhesion of its tyres for the develop- ment, of tractive effort may not prove economical, and a rack-rail locomotive or a rope haulage system should be installed. When taking up the design of the separate elements effective in mine operation, we must bear in mind that all the elements are correlated and that there are definite limits to the output which control the development and extension of each. The size of the shaft and the depth of the hoist are good examples of governing conditions predetermined and restricting. It would be mere folly to overdevelop the haulage system to produce a tonnage greater than that which could be handled by the hoist. After an analysis of existing conditions indicates that a saving is possible by improving a haulage road, an estimate must be made to determine the approximate amount which may be profitably spent in making the improvement. To simplify the proposition, the discus- sion will be made directly applicable to haulage with locomotives depending on adhesion of the tyres to the rail for tractive effort, and the estimated value of the improvement will be based on a separate investigation of each of the three classified advantages accruing. These advantages are:—(1) A reduction in the general mining labour cost; (2) reduction of the power cost per ton hauled; (3) reduction of the general expense, in eluding the saving made possible by the. postponement, either temporary or permanent, of expenditures for additional equipment such as locomotives, electric generating units, engines and boilers. Some one operating condition usually limits the mine capacity, and good management necessitates an adjust- ment of all other expenses to meet this condition. A certain amount of delay is unavoidable, and in order to keep one department, which is being pushed to its maximum capacity in continuous operation, other depart- ments may necessarily be carrying a greater labour expense than is actually required. If, therefore, the maximum capacity of the limiting department is increased, the others will approach more nearly their true efficiency. For example, if a main haulage motor pulls a certain number of extra cars per trip as a result of grade reduction, the total number of tons produced by the mine may be increased without a proportionate increase in the general labour cost. To express this saving by a formula, let— t = tons produced per shift before increasing the tonnage; T = tons produced per shift after increasing the tonnage by pulling extra cars per trip ; c — labour cost to produce t tons expressed in dollars; C = labour cost to produce T tons ; S - saving per ton in dollars resulting from the increased tonnage. Then— S = c 4- Z — CAT For example, a certain mine with one main line haulage motor making 16 trips in eight hours from two partings produces 950 tons of coal per shift at a cost for bottom labour of 145’38 dols.; top labour, 52’69; or a total labour cost of 198’07 dols. If the grade on one of the runs is reduced, the motor will easily pull 1,000 tons. To accomplish this, the extra labour cost will be eight hours for one driver and one hour for a track layer per shift. The total labour cost would then be 201’45 dols., and the total cost, including 1 dol. per shift for feed, care and depreciation of the mule, would be 202’45 dols. The saving per ton produced would be— S = 198’07 4- 950 - 202’45 4-1000 = 0’006 dols. If a summit is lowered, the power required to over- * Coal Age. come grade resistance is less; and by increasing the number of cars per trip less power is required per ton of coal hauled, as the proportionate ton mileage of the locomotive itself is reduced. The weight of the loco- motive inbound may perhaps be one-third and outbound one-fifth of the total weight of the trip. It is plainly evident that considerable energy is required to move the locomotive alone. The cost of power may be further reduced by obtaining a high load factor. The maximum energy demand of the motors on the grade will be the same, it being pre-supposed that the largest number of cars will be pulled at all times, depending on the grade ; but the average power consumption of the motor will be increased at all other points on the trip, thus affecting the load factor for the entire mine. The results of many observations show that a definite relation exists between the cost of production of elec- trical energy and the load factor. With a small plant of one unit, as usually installed at a coal mine, the cost of power at no load is excessive, being approximately one-third to one-half that of full load. On account of the terms of a contract with the miners’ union the labour cost is usually a constant, and the only difference in the cost between no load or part load and full load is in the amount of coal and supplies used. The advantage of keeping the plant load uniformly near the rated capacity without high peaks is plainly evident, and in case the power is purchased from a central station, the saving may be considerable by obtaining a sliding-scale contract providing for this feature. In order to express by a formula the total value of the power saved, let— n = the number of trips made by the locomotive per shift; g = gross weight of locomotive and trips, both loaded and empty, when the mine is producing t tons of coal; G = gross weight of locomotive and trips, if the mine produced T tons of coal through adding x cars to each trip ; (T— t) = (G — g) n — increased tonnage hauled; L = net tonnage of locomotive alone for all trips ; Et = the efficiency or percentage of power used in hauling cars when the mine produces T tons; E^ = the efficiency when the mine produces t tons ; K = cost of power per kilowatt-hour expressed in dollars; R — per cent, saved per kilowatt-hour due to reduction of load factor; PT = power used to produce T tons; Ptf = power used to produce t tons; ST = saving from increased efficiency of power resulting from a reduced ton mileage of the locomotive; 52 = saving per ton from reduction of the load factor; 53 = saving per ton due to lowered summits or of rise and fall, acceleration and braking power losses not being considered; Sp = total saving per ton of coal produced, in power cost resulting from an increased tonnage produced by reducing the limiting grade. Then— Et = w^en producing T tons; E^ = ---?? when producing t tons ; gn a _ (E* —ET)KPft i T q .__EiKPj “rp - i s- = GM')Ki [(E< — Et) +R]KPt s"= t - (? - It is possible that the maximum power requirement to operate on a ruling grade will call for power- producing equipment with a capacity rating out of proportion to the duties otherwise demanded. If this be true, the overhead charge of interest, taxes and depreciation on the necessary increased expenditure would be chargeable to the ruling grade. In other cases a reduction in grade resistance will render available power needed m the operation of other units, and the expenditure of funds for additional power is deferred. The amount of the interest on the deferred expenditure may be added to the other calculated savings to be expected from the proposed improve- ment. A heavy pull exerted on a limiting grade will also tend to increase maintenance and repair charges for both rolling stock and track. If the grade is reduced, the car repair cost per day may increase, due to the greater number of cars hauled; but the charges per car-mile and the maintenance per ton hauled will remain the same and will not affect the unit cost per ton of coal produced. By cutting down a hill or otherwise improving the haulage, the hazard of operation is greatly reduced. The danger to equipment has been discussed under maintenance and repair charges. The greater hazard, that to human life, although hardly directly calculable, is of vital importance, and must not be overlooked when considering the possibility of any proposed improve- ment. In other words, it is simply applied safety and could be included under the head of insurance. Summing up all the previously discussed advantages resulting from the reduction of a ruling grade, that amount, expressed in cents per ton produced, multiplied by the number of tons available to be hauled over the improved section, will give the total sum that may be expended on the improvement. Let— y — the estimated number of tons available; C = cost of grade reduction, including interest on money invested; S = summation of all savings, expressed in cents per ton; V = value of safe operation. Then (y S -f- V) should be equal to or greater than the value of 0. If the value of y S (the total saving expressed in money) is less than the cost of the improvement, and the value of safe operation does not, in the opinion of the management, overcome the difference, then the project should be abandoned. As a matter of fact, the judgment of the promoter must be relied on throughout the entire investigation. False assumptions may be made in some cases, leading to erroneous conclusions, but by following out carefully each step indicated, it is possible to make a fairly accurate prediction of the results to be attained from a proposed grade reduction. Table I.—Giving the Number of Kilowatts Required to Haul 1 Ton Gross Train-load (as Measured at the Trolley Wire). The total resistance includes the tractive resistance of 20 and 30 lb. per ton on level track and grade resistance up to 4 per cent, inclusive. Velocity in miles per hour. Per cent. 4 5 6 8 10 grade. Tractive resistance in pounds per ton. 20. 30. ^0. 30? Tg. 30? 20. 30. ^0. 30? •0 ...0’2 0’3...0’25 0’38...0’3 0’45...0’4 0’6...0’50 0’75 05 ...0’3 0’4...0’38 0’50...0’45 0’60...0’6 0’8...0’75 1’00 1’0 ...0’4 0’5...0’50 0’63...0’60 0’75...0’8 1’0...1’00 1’25 1’5 ...0’5 0’6...0’63 0’75...0’75 0’90 . 1’0 1’2...1’25 1’50 2’0 0’6 0’7...0’75 0’88...0’90 1’05...1’2 1’4..1’50 1’75 2’5 ...0’7 0’8...0’88 1’00...1’05 1’20...1’4 1’6...1’75 2’00 3’0 ...0’8 0’9...1’00 1T3...1-20 1’35...1’6 1’8...2’00 2’25 3’5 ...0’9 1’0...1’13 1’25...1’35 1’50...1’8 2’0...2’25 2’50 4’0 ...1’0 1’1...1’25 1’38...1’50 1’65...2’0 2’2...2’5 2’75 Formula— -g- _ Tr x v x 0’746 550~x 0’8 Kw. = kilowatts used to haul 1 ton as measured at the trolley wire. (The losses in the line must be added to obtain the total power indicated at the switchboard). Tr = tractive resistance in pounds per ton. . v — velocity in feet per second. Note.—The efficiency of the motor and gearing are taken as 80 per cent, when running with the controller cut out. With the controller in circuit, the efficiency of the motor will be from 60 to 65 per cent. Table II.—Average Cost per Kilowatt Produced for the Various Power-plant Units. Minimum Maximum cost per cost Item. kilowatt per capacity. kilowatt. Dols. Dols. Boilers and settings .... 10’75 . .. 13’25 Stokers 1’30 . 2’20 Flues, dampers and regulators .. 0’60 . 0’90 Boiler-feed pumps 0’40 . 0’75 Feed-water heater 0’20 .. 0’35 Piping, valves, etc 4’20 .. 7’00 Economisers '■..... 1’30 . 2’25 Foundations for engines 2’00 .. 3’00 Engines ... 22’00 .. .. 30’00 Generators ... 16’60 ., .. 22’80 Switchboards and wiring 3’20 .. 4’20 Supervision 4’00 .. 6’00 Miscellaneous 2’00 . 3’00 Total .... 68’55 .. .. 95’70 The values given above may be used to approximate the interest and depreciation on a deferred expenditure for equipment made possible by reducing the limiting grades, thus lowering the maximum energy demands for short periods of time. The saving of interest and depreciation may be considered as a partial payment on the cost of the grade reduction proposed. BRITISH ENGINEERS’ ASSOCIATION. The meeting of this association at the Hotel Windsor on Wednesday, under the chairmanship of Mr. Wilfrid Stokes (president), adopted the revised memorandum and articles of association, as approved by the Board of Trade, in virtue of which the association will now admit engineering departments of public services and also individuals, so as to bring the manufacturer, user, and buyer, as well as the scientific expert, into the closest possible co-operation. District committees and trade sectional committees will be formed, with repre- sentation on the council of the association. The co-operation of existing sectional associations will be obtained to obviate any chance of overlapping in those branches of the industry which are already organised. An interesting discussion took place on the organisa- tion of engineering education and research, and it was decided to appoint a committee to ascertain what is being done by the various bodies at present dealing with research questions, and to see in what directions research work can be made of more practical utility to engineers. The need for the co-ordination of all the educational movements dealing with engineering matters, and the desirability of formulating a very comprehensive scheme was urged. With regard to the operation of the association in China, the president stated that the committee had under consideration proposals of an extensive nature for undertaking general educational and pioneer work with a view of bringing the advantages of the use of machinery to the notice of the undeveloped markets of that country. Further meetings would be held for the discussion of this scheme. In his remarks on the re-construction question, Mr. Stokes urged the importance of establishing more har- monious relations with their workmen, a systematic exploitation of overseas markets, the importance of standardisation and co-operation in methods of pro- duction, and the difficulties of transport and shipping. Economy in Gas Making. — Mr. George Helps, a Nuneaton gas manager, has invented a process which, he claims, will save about 60 per cent, of the amount of coal now used for gas making. It will give eight times the quantity of gas, four times the heat value, and 80 per cent, of efficiency, as against 50 per cent, under present methods. He proposes to make the gas at the pit mouth, and convey it in pipes to where it is required, this being cheaper, he says, than carrying the coal.