1248 THE COLLIERY GUARDIAN. June 21, 1918. tion in the evenings if the hour was possibly extended from 7 p.m , as proposed in the Bill, to 8 p.m. In his own district the lads were all up the pit at 2.30 in the afternoon, or 3.30 at the latest. Even after heavy meals the boys appeared to be quite lively when he saw them running about. If evening classes were arranged from 6 p.m. to 8 p.m., these would, he thought, suit quite admirably. Where pits were double shifted there would probably require to be classes, say from 9 a.m. to 11 a.m. in the forenoons. Mr. Joseph Parker, Fife Mining School, Cowden- beath, indicated that he had a decided preference to the arrangement which permitted boys to come to the school for a full day’s instruction when they were fresh. Not only were the boys in a position to assimilate what they were taught, but the teachers, with the longer time at their disposal, would be able to round oft or complete any particular bit of study or lesson. Frankly, he did not think that the problem of arranging to give instruction to boys for one full day each week was so formidable as members of the institute appeared to consider. The President said he would like to have the methods discussed from the point of view of discipline. For example, did Mr. Parker think that discipline could be as well maintained in a school where the boys only attended one full day per week as compared with an arrangement where the teacher had charge of the boys for four or five nights per week ? Mr. Parker said he did not think there was much in the point of discipline if the teacher had a personality and some individuality. Mr. C. C. Reid, Cowdenbeath, ventured the opinion that the coal pits were reeking with inefficiency. Coal- masters to-day spent hundreds of thousands of pounds on machinery—in installing coal-cutters, conveyors and plant generally—yet they hesitated to spend any money in training or educating lads and men to handle the machinery properly. Why should not the Mining Institute of Scotland take a firm stand and say with some measure of determination, “We are going to propose the right thing now, and we recommend that there should be a compulsory raising of the school age.” In the pits to-day what they really stood in need of was a higher standard of learning and a higher measure of intelligence amongst those who were handling expensive machinery. How, he asked, were they going to secure that higher standard of education amongst the workers underground unless they made provision for all the workers receiving it ? The discussion was adjourned at this point till next meeting. EXPLOSIVES IN COAL MINES. New Order. The Home Secretary has issued under date May 30, 1918, an Order including the explosive known as Haylite No. 3 in the 1st Schedule of the Permitted List. Haylite No. 3 has the following composition:— Parts by weight., t--------N--------' Ingredients. Not more Not less than than Nitro-glycerine............. 10*5 ... 8*5 Nitrate of ammonium ........ 62 ... 59 Wood-meal (dried at 100degs. C.) 6 ... 4 Chloride of sodium........... 20'5 ... 18*5 Oxalate of ammonium ............ 6 ... 4 Moisture...................... 2 ... — The explosive shall be used only when contained in a case of paper thoroughly waterproofed with carnauba wax; with a detonator or electric detonator of not less strength than that known as No. 7 ; and the greatest weight of the explosive which may be used in any one shot-hole shall not exceed 16 oz.; the explosive must have been made at the works of the National Explosives Company Limited, Upton Towans, Gwithian, in the county of Cornwall. Four ounces of Haylite No. 3 gave a swing of 2*44 in. to the ballistic pendulum compared with a swing of 3'27 in. given by 4 oz. of gelignite containing 60 per cent, of nitro-glycerine. Coal Mining Industry in Holland.—The coal mining industry of Holland developed with remarkable rapidity in the first decade and a half of the present century, and the tendency to further growth continues in undiminished proportion. The average annual increase since 1914 has been about 16^ per cent. The number of mines working- increased from four in 1906 to eight in 1916. An official report made in 1910 estimates the future output at 4 million tons in 1925, 6 million tons in 1935, 6£ million tons in 1945, and over 8| million tons in 1950. Control of Coal Mining—Speaking on Saturday at the annual meeting of Pease and Partners, Mr. Arthur Francis Pease declared that he was certain that at present in the northern area there was a heavy loss on every ton of coal worked and the new comb-out would make it worse, for it was impossible to reduce the cost in proportion to the reduction in output. It was serious, and something must be done by the Coal Controller. Regarding the conditions which would prevail after the war, he said he anticipated in the coal trade a hiatus between the time the Govern- ment required enormous munitions and the time when conditions returned to the normal state. Men who had worked hard and continuously would require a holiday and soldiers a furlough before starting work, and it would be necessary to shut down some works for a time, and he felt they must look for a difficult period. He felt the Government must abolish control immediately at the close of hostilities. It seemed at one time that because of the. shortage of shipping it might be necessary to have rationing of raw material and food for a period after the war, but the shortage of shipping, it appeared, would not be so great as was anticipated, owing to the enormous efforts of this country and the United States to increase tonnage, and he saw no reason why their trade should not be put on the normal basis of supply and demand the day peace was declared. ESTIMATING INJURIOUS DUSTIN MINE AIR BY THE KOTZE KONIMETER. By John Innes. The study of miners’ phthisis has led to the classifi- cation of dust in mine air into two types, known respectively as “injurious dust” and “ non-injurious dust.” Reference to the report of the Miners’ Phthisis Prevention Committee, 1916, will show that the majority of particles extracted from the lungs of miners who have succumbed to this disease is less than 2 microns (1/12500 in.) in diameter. Thus the term “ injurious dust” might correctly be confined to such particles. For practical reasons, and any error is on the safe side, the definition has been made to include all particles up to 5 microns in diameter, and it is in this sense that the expression is used in this paper. We are indebted to the perseverance and ingenuity to Mr. R. N. Kotze, the Union Government Mining Engineer, for a simple solution by means of an instru- ment he has devised and called a “konimeter.” The Konimeter. The Konimeter is a simple mechanical arrangement for causing a known quantity of air to impinge at a high velocity through a fine nozzle on to the surface of a glass slide which is thinly coated with vaseline. Fig. 1. A—aluminium body; B—bore l|mm. to 6mm.; C—cup leather;* D-leather joint; E spring steel; F—rubber ring; G—glass slide; H—leather pad; I—|mm. space between nozzle and G. 222234 ■D Fq Hl I I - » Fig. 2. The method of accomplishing this can be readily followed from the working drawings (fig. 1). A piston, actuated by a spiral spring, is contained in a cylinder of such a size that on release of the spring which is held compressed by a trigger-catch, it moves through a space equivalent to 5 cc. This small intake pump is mounted in a handpiece in such a way that it can draw air from a cell which is formed by an annular rubber ring attached to the frame, and a vaselined glass slide which is pressed against the ring by a flat spring, thus making an air-tight joint. This cell communicates with the outside air through a conical nozzle which tapers in diameter from 1-5 mm. to 0-6 mm. The small end of the nozzle is adjusted close to the glass slide. On each intake stroke of the piston air rushes up this nozzle and deposits its dust content in a circular spot. The size of this spot depends upon the amount of dust in the air, and is usually 0-6 mm. to 1 mm. in diameter. Two or more puffs may be used to form a single spot if it is thought that the dust content of the air is low. The size of the nozzle, and the speed at which the piston moves, show considerable variations in different models of the konimeter. Nozzles are in use from 0-6 mm. to 1 mm. in diameter at the small end. For the purpose of determining the piston speed Mr. Kotze has designed a simple apparatus consisting of a cali- brated timing rod to which a bristle, or a piece of fine wire, is attached, and a simple catch, which operates the trigger of the konimeter and vibrates the timing rod simultaneously. The vibrations of the rod are recorded on a blackened sheet of paper or mica which is fastened to the konimeter by a metal * Paper read before the Chemical, Metallurgical and Mining Society of South Africa. clip—this clip fitting in between the guide and the spring. The arrangement gives an accurate measure of the time taken for the piston to complete its stroke, and from this the velocity of the air through the nozzle may be easily calculated. Tests made with a large number of konimeters show variations in air velocity between 20 and 175 metres per second, and Mr. Atkin finds that a velocity of less than about 30 metres per second will not produce the adherence of all the fine dust, while a velocity of 175 metres per second causes the vaseline to spread unless the coating is very thin and even. Velocities between 30 and 120 metres per second give satisfactory results. As many as nine spots may be made on the slide by slightly moving the glass slip after making each spot. It is usual to arrange these spots in parallel rows. On the Ferreira Deep, when the instrument is in use four to six spots are taken on each slide. For example, in a drive six spots might be taken at equal distances from the entrance to the face. These then form a guide not only to the condition at the face, but also to conditions which previously existed. In a stope one spot would be taken of the air entering the stope, another of the air leaving the stope, while the remaining four would be taken at different places in the stope. The slides used are 1J in. by 1 in. glass slips with ground edges. These are cleaned after use, and should be polished with a soft cloth before the appli- cation of the vaseline. The vaseline may be applied with the finger or by the flat piece of rubber, but the best result is obtained by spreading it with a glass rod. The coating should be as thin and smooth as possible. Before use the slides are examined under the microscope to see if the vaseline is free from dust, and, if so, they are then placed, vaseline downwards, in a metal container which holds two slides. The metal containers are shaped as shown in fig. 2. The recess prevents contamination of the vaseline and preserves the spots. The slides are attached to these containers by rubber rings. In removing slides the rubber ring should be rolled down to near the end of the frame, when one slide can be readily taken out without danger of moving the other. A box to contain six metal holders and the konimeter will be found convenient for taking underground. The konimeter is provided with a spare glass slide, which is coated with vaseline and placed in position. Before taking a sample several puffs are made on to this slide to remove all trace of the last sample which might remain in the nozzle. On cold days moisture in the nozzle must be removed before taking samples, unless the konimeter has been warmed before taking it underground, when moisture will not form. Since the introduction of the Kotze konimeter another type has been made which utilises the same principle. Instead of taking the spots on microscope slides, the spots are formed near the periphery of a circular disc of glass. As many as thirty spots may be taken on each disc. These discs are not so easily handled under the microscope, and actually thirty samples could not be taken, as it is necessary to remove the traces of the previous sample from the nozzle after eacfy set of spots by making several puffs. It may be urged that there is less danger from contamina- tion, but this may be neglected because contamination seldom occurs with the Kotze konimeter. The spots taken on the microscope slides used with the Kotze konimeter can be preserved by cover glasses, and may be photographed later should it be desired. The Microscope and the Method of Counting. The stage of the microscope should be marked off so that spots may be readily found. Some difficulty may be experienced in obtaining the correct combination of objective and eyepiece. The size of the field depends on the objective and on the tube length, and it should be at least 1 mm. in diameter and not greater than 1-5 mm. The ruled glass is divided by lines 0-5 mm. apart so that if this is examined under the microscope two to three divisions should be visible. A | in. objective gives a field of suitable size, any necessary adjustment being made by altering the length of the microscope tube. It is advisable to use a high-power eye-piece. The method of counting the number of particles in a spot is important, and here a method is proposed which is theoretically perfect and very simple. It was adopted on the Ferreira Deep at the suggestion of Mr. Selby. A circular cover glass is placed on the dia- phragm of the eye-piece with lines making an angle of 18 degs. with each other, so that a count of the total dust in both sectors is one-tenth of the total count of the spot, i.e., r ’ 360° Two lines are ruled out- side the sectors at such a distance that they appear to be 5 microns apart, as a guide to the eye to enable the size of the particles to be estimated. If a spot is produced by a 5 cc. puff the dust in both sectors will equal the dust in 5/10 cc. = 0-5 cc., so that twice the count gives the dust per cc. If a 10 cc. spot has been taken the count gives the number per cc. direct. The sectors are divided by lines 50 microns apart to facilitate the counting of large numbers of particles. The ruling of the lines so that they will be 5 microns apart presents no difficulty. Assume that the field is 1 mm. in diameter and that 20 divisions ruled 0-5 mm. apart are visible when the ruled glass is placed on the diaphragm of the eyepiece. We then have on looking through the microscope: — 20 divisions = 1 mm. field = 1,000 microns. 1 division = 1 / 20 mm. field = 50 microns. 1/10 division = 1 / 200 mm. field = 5 microns. and as each division is | mm. wide, it will be neces- sary to have the lines ruled 1/20 mm. apart to obtain the 5 micron lines. The eyepiece may be turned round and additional sectors counted, if desired. If the amount of dust is small the whole spot can be counted. The result is usually expressed as the number of injurious particles (under 5 microns) per cc., and the percentage which this number bears to the total count is also given. The following objections have been raised against