706 THE COLLIERY GUARDIAN. April 14, 1916; day. The coal remains, on an average, 48 hours in the bunkers for final drainage, after which it is discharged through four openings at the bottom of each set of bunkers into the scraper conveyors, which deliver the coal to the disintegrators. The crushed coal is fed on to a belt conveyor, which delivers the coal into the coke oven service bunker. The fine coal with the slurry is deposited in the drain- ing bunkers, with an excess moisture of about 15 per cent., and it is anticipated that 8 to 10 per cent, will percolate through the drain pipes and slides at the bottom of the hoppers during 48 hours. The drain water flows to the drain sump, and is then pumped into the. settling tank. A washery with draining bunkers is split up into two distinct parts, which require separate supervision and workmen. At least one man will be required to regulate the coal from the drainage bunkers into the scraper con- veyor, another to attend to the crushers and the belt conveyor to the service bunker, and, in addition, three men will be required in the washery, whereas, with the continuous plant, three men alone are ample to attend to the whole of the work to be done, instead of five with what may be called the “ intermittent ” process. With the continuous washery, however, storage is not provided, and in case of a serious breakdown the coke ovens might go short of coal, if the service bunkers at the time should be empty.. These service bunkers are usually calculated to give a two days’ supply to the coke ovens, or enough to keep the ovens going over the week- end. If a breakdown should occuir, say, on a Monday morning, when the service bunker is practically empty, the coke ovens would have to be stopped for the time being. With draining bunkers of 1,600 tons capacity, 1,400 tons of coal should always be available for supplying the coke ovens during regular work. The drainage capacity of a washery, however, cannot be reckoned as storage also, as the coal has to remain in the bunkers for 48 hours before it is sufficiently dry to go to the coke ovens. The coke ovens, in this instance, require 3,200 tons of coal per week, or, say, 20 tons per hour per 24-hour day. 48 X 20 = 960 tons of coal, or, say, five bunkers out of eight should be left until washing is recommenced, leaving a net storage of 400 tons. This figure may be increased by reducing the time allowed for drainage, and by charging wet coal into the ovens, but the ovens would suffer too much if this practice were often resorted to. With bunkers there is, however, the advantage that, in case of a breakdown, it is immediately known what stocks are in hand, and the working of the coke ovens may be so regulated as to take the coal in the storage bunkers short of a minimum that must remain to allow sufficient time for the new coal to drain properly. On the face of it, the draining bunkers seem to have the advantage, provided that there is not much difference in price : but by'installing a service bunker of an addi- tional 400 tons capacity, the advantages are all in favour of the continuous washery :— (1) There is the saving of two men, which alone repre- sents at .least 1*150 in wages per year. At 10 years’ purchase, this would probably more than equalise the increase in cost for the larger service bunker, not to mention the advantages of managing the plant with fewer men, especially under existing labour difficulties. (2) The draining conveyor receives the wet coal at one end, and delivers the dry coal automatically at the other end. There is no trouble arising from coal sticking in the conveyor—so very common in the case of drainage and storage bunkers. (3) The draining conveyor moves only very slowly— about 18 in. per minute—in comparison with the dis- tributing and collecting conveyor in connection with bunkers, which rarely travels at less than 75 ft. per minute. The wear and tear, therefore, of the draining conveyor is negligible as compared with the fast- running conveyors. There are two further points to consider in the lay-out of the washery, one of which is very often entirely overlooked, namely, siding accommodation, which may became quite important with washeries of large capacity, especially when the coal is brought in railway wagons.. Another difficulty to overcome, especially where washeries are connected direct,to the screening plant, is the irregularity with which the coal arrives; and although the washery may, on an average, have to deal with 1,000 tons of coal in eight hours, the coal during this time may arrive at the washery at the rate of 250 tons per hour, which with a 125-ton-per-hour washery could not be-dealt with at this rate. Sidings are provided for stocking empty wagons at the upper end of the washery for a whole day’s washing, with sufficient room at the bottom end to allow the loaded wagon to collect there. Separate sidings arc arranged for each size of washed coal, so. that no shunt- ing operations whatever are required to deal with the whole of the coal in the washery. The coal is delivered by means of a bolt conveyor of a capacity of 200 tons per hour direct into a feed hopper of 900 tons capacity. A separate feed hopper of 100 tons capacity is arranged at the top of this bunker, to which one of the feed elevators for the washery is attached. If at any time more coal arrives than the washery can deal with, the surplus automatically falls into the large storage hopper. A separate elevator is attached to this largo hopper, which elevates the coal into the washery when required. Imports of Pit Props.—During March, 196,422 loads of pit props were imported into the United Kingdom, the value being £614,112. The imports in March last year were 185,265 loads, value £301,294; and in March of the preceding year, 176,476 loads, value £176,788. The total imports during the first three months of the year were 488,457 loads, valued at £1,400,952, as compared with 433,786 loads, valued at £676,662 in the corresponding period of 1915. CURRENT SCIENCE Pulmonary Disease Amongst Miners. Technical Paper 105, issued by the United States Bureau of Mines, contains a preliminary report on “ Pulmonary Disease Among Miners in the Joplin Dis- trict, Missouri, and its Relation to Rock Dust in the Mines,” by A. I. Lanza and Edwin Higgins. The report states that in recent years there has been an unusual prevalence of pulmonary tuberculosis and a high death rate from it among the metal miners in South-Western Missouri. The records of the State Board of Health for the calendar year 1912 show a death rate from this disease of 200-8 per .100,000 population. The device used for sampling the dust is shown in the illustration, and consists essentially of the following parts :—A glass bulb or container for the filtering medium. This bulb is partly filled with granulated sugar. The granulated sugar is prevented from passing into the sampling device by means of a perforated glass plate inserted in the bottom of the glass bulb. That part of the oxygen-breathing apparatus known as the mouthpiece, with inhalation and exhalation tubes attached. The moutlupiece may i. e held securely in position, when the device is in use, by means of a cap, to which straps are attached. It is not necessary, how- ever, to use a cap when one becomes familiar with the device. A nose clip to prevent air from passing in or out of the nostrils, and what is known as a Draeger litre bag, having a capacity of 35 litres, are included. In order to collect a sample, the apparatus is adjusted in the mouth with a dust bulb and litre bag attached.' The nose clip is then placed on the nose, and the person taking the sample breathes naturally. When air is Apparatus for Determining Rock Dust in Mine Air. •' <4 .''J* <■ . d5* *■ A * '** I MB inhaled, the valve in the inhalation tube opens, allow- ing the air to pass to the lungs; at the same time the valve in the exhalation tube closes, making it impos- sible to draw air from the litre bag. When air is exhaled from the lungs, the valve in the inhalation tube closes and that in the exhalation tube opens. In taking a sample, then, the air passes through the bulb (where the dust is intercepted by the sugar) into the lungs, and thence through the exhalation tube to the litre bag, where it is measured. Ordinarily, sufficient accuracy may be secured by inhaling and breathing out a total of 35 litres of air. However, if the place in which the sample is taken is only slightly dusty, the bag may be filled a second time, thus making a total of 70 litres of air for the sample. In order to determine the amount of dust collected, the contents of the bulb are washed out into a weighed Gooch crucible, and dried at 105 degs. Fahr. After successive washings with water, to dissolve and remove all of the sugar, the crucible is again dried at 105 degs. and weighed. The increase in weight represents the weight of rock dust in the sample. The air exhaled from the lungs occupies about one-fiftieth less volume than the air that is inhaled. This is not an appreciable error, and may be corrected easily. Ifhc following conclusions may be set down regarding the production and prevalence of rock dust in the Joplin sheet ground mines :—(1) Rock dust is produced by the blowing of dry holes, squibbing, boulder popping, drill- ing without water, shovelling, tramming, roof and pillar trimming, and the dumping of the bucket on the sur- face; (2) the mine workings constitute practically one large open chamber, which allows the dust to dis- seminate more quickly than would be possible in more restricted workings; (3) although the amount of dust in the air is not comparatively large, practically every man underground is exposed to a dusty atmosphere during his entire shift; (4) most holes are drilled nearly horizon- tally—such holes produce less dust that those drilled AND TECHNOLOGY. upward; (5) the rock dust particles are made up almost entirely of flinty chert, which breaks with splintery and knife-like edges. The investigators recommend that the following means should be employed for the abatement of rock dust in the mines :-— (a) Provide a water supply for every working face by the laying of a separate water line. (5) Where drills are operated without water, attach to the hose leading to the face a 5 or 6 ft. length of pipe, with a nozzle from J- to in. in diameter. Make and enforce such regulations as will ensure the use of this water spray for the purpose of wetting drill holes, the face, and the broken rock about the face. For the purpose of washing drill cuttings from drill holes, this hose may be attached to the long pipes now in use for blowing out drill holes. (c) Where there is in use some type of drilling machine that provides for water passing through the core of the drill "steel into the drill holes, make and enforce regulations that will ensure the spraying of the face and broken rock for short periods at such times as the drill may not be in operation. For this purpose the water hose must be uncoupled from the drilling machine unless separate water connection is provided. (d) Make and strictly enforce rules against squibbing and boulder popping while the shift is underground, and against the blowing of dry holes at all times. (e) Improve ventilation by the opening of new shafts whenever practicable. They add the following injunctions :—Do away with common drinking cups andjjegs, and water pipes which allow the miner to bring his lips in contact with the orifice. Substitute the well-known sanitary drinking fountain when practicable, or have the miners bring their own water supply in individual containers. Do not employ as shovellers men under 20 years of age. Through co-operation among the miners, provide a maximum daily tonnage for shovellers, so that they cannot injure their health through overwork. Provide a warm, dry, and clean place in which the miners may change their clothes. Through intensive educational campaigns in the public schools, and among the miners themselves, disseminate information as to the harmful effects of insanitary practices and conditions, such as crowded living quarters, overwork, exposure, dissipation, the breathing of air polluted by powder fumes and rock dust, and the use of common drinking devices. Toluol Recovery. In his presidential address to the members of the Manchester Institution of Gas Engineers, Mr. E. A. Harman referred to the production of toluol for war purposes. Various suggestions had been made, he said, for increasing the yield of this. “ For instance, there is Rollason’s method of mixing the coal with a small percentage of unburnt limestone. This process appears to be based on the idea of gener- ating a gas in the retort at the same time the coal gas is being made, in order to sweep out the gas rich in hydrocarbon vapours, which would be evolved at the beginning of the charging time—probably during the first hour or so after the charge has been put into the retort. There seems to be some doubt as to the advan- tages obtainable from the method. My own opinion is that it is not all that is desired. What is required is a gas already formed that can be turned on at the lid of a through retort as soon as it is closed, so as to sweep out the hydrocarbon vapours as soon as they are pro- duced and at their maximum. There is nothing new in this idea; indeed, it was mentioned at one of the London meetings some 17 years since by the lamented Prof. Vivian B. Lewes, who also suggested blue water gas for a similar purpose. Li removing the toluol, all or nearly all the condensable hydrocarbons—i.e., benzene, xylene, toluol, etc.—are removed by the washing oil or tar, so that if a measure of the condensable hydrocar- bons or hydrocarbon vapours can be made at the inlet and at the outlet of the washer, the amount of work done by the washing can be obtained, and a fair esti- mate of the amount of toluol removed can be found, especially if the amount at the inlet of the apparatus has been determined by the washing test. There is at least one way in which this can bo done; that is, by making a determination of the . condensable hydro- carbons or hydrocarbon vapours at the inlet and outlet by means of alcohol in the Hempel apparatus.” A New Industrial Disease. The Health of Munition Workers’ Committee have recently issued a memorandum dealing with certain industrial diseases to which munition workers are speci- ally subject. Amongst these may be mentioned the eczematous affections to which the manufacture of trinitrotoluol gives rise. The extended use of this material, in the production of which collieries are largely engaged, has brought its poisonous properties into pro- minence. Operatives employed in its manufacture and in loading it, either pure or mixed with other substances, into munitions have been found affected with unusual drowsiness, frontal headache, eczema, and loss of appetite. Exceptional cases may occur with sudden collapse after a few hours’ work on a hot day, but generally the symptoms are at first slight, ,and, if expo- sure ceases, quickly disappear. If, however, the exposure be continued, the symptoms tend to become more severe, and may bo associated with cyanosis, short- ness of breath, vomiting, .anaemia, palpitation, bile- stained urine, constipation, rapid weak pulse, pains in the limbs, and jaundice; while in a few cases profound jaundice with danger to life has supervened, and even death has resulted. Trinitrotoluol, like nitro-derivatives of benzene, may be absorbed by inhalation of vapour or dust, through the skin, and through the digestive tract;