November 8, 1918. THE COLLIERY GUARDIAN. 969 The Taking Gas Samples. After the temperature of the parts of the apparatus had become more nearly uniform, samples of gas were taken in the manner described below. In this sampling, and in the taking of all other samples, the samples were drawn as nearly simultaneously as possible from the top and the bottom compartments so as to reduce the pressure equally in both. The two levelling bottles were placed at the same distance below the height of the column of liquid to which each was connected in order to give the same amount of suction in each sample tube. First about 5 c.c. of gas was withdrawn and expelled into the air in order to bring fresh gas into those parts of the connecting tubes that were not filled with the glycerine solution. Then from each compartment about 50 c.c. was drawn for samples. Diffusion of Oxygen. Immediately after the taking of the first pair of samples diffusion was started by quickly removing the diaphragm from the surface of the coal, time of removal of the diaphragm was recorded and considered as the starting time of the diffusion. The sample tubes containing the gas were dis- connected and the percentage content of oxygen determined with a Haldane apparatus. In this and subsequent determinations the small amount of carbon dioxide in the gas was removed before determination of the oxygen and the percentage of oxygen calculated on the basis of a gas free from carbon dioxide. At regular intervals samples of gas were taken, in the manner described, and analysed. The time of taking the sample was recorded to the nearest minute. During the experiment there was not only a diffu- sion of oxygen from the lower to the upper compart- ment, but also a diffusion of nitrogen from the upper compartment to the lower. The results obtained by analysis measure the combined effects of these two processes. For the purpose in view, however, only the diffusion of the oxygen need be considered. While diffusion was taking place, the composition of the gas in either the lower or upper compartment k I2 k e d h h Q,g c Fig. 1.—Vertical Section of Lower Part of Diffusion Chamber. ’0's b aV' Fig. 2.—Vertical Section of Upper Part of Diffusion Chamber. could not have been uniform, but must have differed at different heights in the compartment. By drawing the samples from the centre of the compartments it was presumed that gas of average composition was obtained. Practical Applications of Results. The results of the experiments showed especially the importance of the proportion of voids in a mass of stored coal exposed to the air in determining the possible amount of oxidation through oxygen entering the mass by diffusion. The amount of voids in any mixture of coal pieces can be kept low by having the large and small size coal uniformly mixed. If the proportion of small coal to large were such that the volume of the small were just enough to fill the voids in the larger size, and’ this process repeated indefinitely with still smaller sizes, a limit of no voids would be approached. In practice such an arrange- ment could not be made; but, on the other hand, it is an ideal to be approached as nearly as practicable. Separation of fine and of coarse coal is incident to most methods of handling coal. This separation serves to increase the amount of voids in the segregated parts of the mass. Segregation takes place very readily when a pile is made, as is usually the case, by adding each increment at the apex of the pile. Most of the largest lumps then roll to the bottom, and there is a somewhat regular gradation of sizes up the side of the pile, with the smallest sizes at the top. As the result of investigations of spontaneous fires in coal on shipboard, the New South Wales Commis- sion found that in every instance investigated the spontaneous fire originated in the heap of dust under the hatchway. Dust particles expose a larger surface per unit of weight to the action of oxygen. But, such considerations aside, this investigation of diffusion explains how segregated dust in a mass of coal receives more oxygen from the outside air by diffusion than it would receive if the same mass of coal had been stored so as to have a lower proportion of voids. Segregation in coal piles may be largely prevented by carefully building the pile so as to prevent coal rolling down the sides. The ground on which the pile is to stand may first be covered evenly and com- pletely with a layer of coal. On this first layer a second layer may be placed with equal care, then a third, and so on. It has been shown that a mass of very small uniform coal particles has no practical effect in retarding the diffusion of oxygen through it, and the proportion of voids in very fine coal, when uniformly sized, is the same as in lump coal when uniformly sized. However, it might have been expected that the smaller size would retard diffusion because of increased friction between coal and gas molecules, each of which has its own velocity, owing to the greatly increased surface of contact. That very fine coal oxidises more readily than coarse and is more liable to spontaneous combustion is well understood. In addition to the greater danger from other sources, under otherwise similar conditions, the experiments described show that by diffusion oxygen is brought from the air to the interior of a mass of fine coal just as readily as to the interior of a similar mass of larger sized coal. Conclusions. The results of the investigations may be summed up in these conclusions. 1. The principles stated in Fick’s law of diffusion have been found applicable to the diffusion of oxygen through the atmosphere in the voids of broken coal. 2. In a mass of broken coal through which oxygen is diffusing, the size of the pieces has within prac- ticable limits no effect on the rate of diffusion, all other conditions being constant. 3. If the proportion of voids in a mass of coal pieces is varied, the time required for a definite diffusion of oxygen increases approximately in inverse propor- tion to the percentage of voids. The product of the percentage of voids and the time required for a given diffusion increases directly with the increase in the percentage of voids. 4. The amount of oxygen diffusing through the interstices in a mass of coal pieces seems to vary inversely as the depth of the coal. Enough experi- ments to justify a more definite conclusion have not been made. 5. Coal stored in lumps or smaller pieces of uniform size contains a high proportion of voids, and oxygen diffuses readily through the mass. In run-of-mine or slack coal, which contain a great variety of sizes, the proportion of voids is less and the diffusion of oxygen is slower. 6. Mixing different sized pieces in a mass tends to reduce the proportion of voids. In storing coal in the air, factors other than diffusion may be accelerated or retarded by changes in voids; but if diffusion alone be considered, mixing the sizes of coal will reduce the oxygen entering the pile by diffusion. 7. Building of a coal pile so as to reduce or prevent segregation of the large and the small pieces will lessen the proportion of voids in the pile, will tend to keep down the amount of oxygen entering the pile by diffusion, and thus reduce oxidation from this source. Safety Lamp Glass Order.—The Home Secretary has made an Order, under section 33 of the Coal Mines Act, 1911, entitled “ The Safety Lamp Glasses Order of October 25, 1918.” The effect of the Order is —(1) To repeal the emergency order of November 6, 1914, which sanctioned temporarily the use of unapproved glasses, and (2) to remove from the approved list of safety lamp glasses all makes of glasses other than the six makes named in the schedule to the Order. Coal and Potash for Allied Chemists. — M. Paul Kestner, president of the Societe de Chimie Industrielle, which was formed about 18 months ago, was the guest of the Society of Chemical Industry at a luncheon in the Cannon Street Hotel on Monday. Prof. H. Louis, who presided, observed that the importance of identity of aim was not so fully recognised as it might be. We heard a good deal about national reconstruction, but international re- construction was also needed. The Allies commanded all the raw materials that the chemical industry needed except one—potash, of which Germany, through a pure geological accident, had up to the present had a monopoly. When France regained the provinces which had been wrested from her, the potash monopoly would be a monopoly no longer. France had always depended on us for a con- siderable proportion of her coal supply, and she was more than ever dependent now that her principal coal fields had been wrecked by the enemy. In both countries after the war labour would be dear and scarce for a long time. No one expected or wished wages to return to pre-war standards, but they did ask that the worker should give a fair day’s work for a fair day’s pay, and that artificial restrictions on output should be absolutely done away with. The main work of the societies in the future lay in the fullest scientific training of the staffs of their great chemical industries and in furthering the closest co- ordination between science and industry. Replying to a toast, Dr. C. C. Carpenter said that the Society of Chemical Industry began in 1881 with 300 members. Probably by the end of this year the number would be 5,000. IMPROVING BOILER ROOM EFFICIENCY.* By A. H. Blackburn. As the largest item of expense is fuel, the first consideration should be given to buying carefully the coal that will give the best results commercially. Coal giving the highest boiler room efficiency may not commercially be the most economical—the volatile grade of coal selling at a lower price giving 68 to 70 per cent, of efficiency may work out a “ better buy ” than a higher-priced coal giving 75 per cent, efficiency. Coal should therefore be bought on price and a guaranteed analysis, with clause covering reduction or advance in price according to the quality actually supplied, etc. Whether coal is bought on analysis or not, sample should be frequently taken and analysed to check up what efficiency is being obtained. For this purpose an approximate analysis will be sufficient, giving moisture, volatile combustible, fixed carbon and ash. Enough consideration is not given, in buying coal, to the matter of ash as regards its fusing point for the successful working of the type of grate or stoker installed. Tests made with under-feed stokers show that some ash will fuse at a temperature of over 2,500 degs. Fahr, and is classed as non-clinkering, and other ash under 2,500 Fahr, and is classed as clinkering, One should avoid ash that contains silicate less than 30 per cent.; alumina less than 30 per cent.; iron oxide above 15 per cent.; lime above 10 per cent.; magnesia above 3 per cent.; but it must be borne in mind that coals with a low ash are the most efficient, both from a theoretical point and a practical point. More ash means more labour in handling the fires and carrying away the ashes. Also, a greater air pressure is required and there is greater loss through infiltration of cold air through the boiler settings. The small losses should be looked after, as otherwise they will amount to a large item in the course of a year. The following suggestions may be useful:— 1. Examine carefully the brick work of the boiler setting for cracks which will allow infiltration of air into the combustion chamber, and for air spaces around the structural steel supporting the boiler. Any such cracks and openings can be detected by examination with a candle. If there are any openings the flame will be drawn in. Another method consists of shutting down the chimney damper for a moment immediately following a full firing with green coal, thus causing the smoke to come out of any crack that may exist. 2. See that all fire, ash and inspector doors are close tight. 3. See that all steam pipes are properly insulated with 85 per cent, magnesia covering, or its equivalent. 4. Examine all boiler feed pumps and auxiliaries to see that they are not wasting or blowing steam through the piston rings. 5. Have the boiler flow-off valve pipe outlet exposed to view so any leaks will be detected quickly. 6. Immediately stop any and all leaks at joints in the steam pipe connections. 7. Have a smooth boiler room floor and see that all the loose coal is swept up, otherwise it is mixed with the ash and lost. Every boiler house should be equipped with three draught gauges, or one draught gauge with three connections, to test the pressure in the air chamber under the stokers or grates, over the fire and outlet to the breeching or stack—(by this means air holes in the fire as well as the use of too much or too little draught for best results can be detected); recording steam pressure gauge; water meter; CO2 recording machine; high temperature thermometer, registering up to 1,000 degs.; coal scales (recording or otherwise); feed water regulators. With these instruments at hand, results can be checked up at any time, and poor results can be detected immediately. Again, no plant can be highly efficient without full consideration of the human element, and the boiler house equipped with the instruments suggested above is able to get best results from the firemen who learn to take pride in their work, and to aim for results that bring encouragement from the chief engineer. It should also be remembered that a boiler room well ventilated in summer and warm in winter adds to the efficiency. In the modern boiler house coal is handled mechani- cally direct into the stoker hoppers. But in many boiler plants of smaller size this is not always possible, and the entire operation is accomplished by manual * The Coal Trade Bulletin.