June 6, 1913. THE COLLIERY GUARDIAN 1213 Table I. (1) Description of coal. (2) Ash. (3) Iron. | (4) Oxygen absorbed at 0 deg. Cent. (5) Calories of heat evolved. (6) Calories evolved per cubic centimetre of oxygen absorbed. Top softs, containing 43 per cent, of pyrites* Per cent. 40 1 j Per cent. 20’2 Cubic centimetres dry at NTP. 321 1,158 3*6 Anthracite — 132 495 3’6 Top coal 1-1 0*1 459 1,275 2*8 Bullhurst ... 3*2 1*2 60 234 3*8 Hard coal No. 1 6*0 0*1 195 705 3’6 Top softs:— First part 2*8 0*8 534 1,684 3*2 Second part — — 1,041 3,089 3'0 Hard coal No. 2 4*0 0*1 1,110 3,196 2*9 Slack 3’2 1'4 31 115 3’7 Iron pyrites from coal* ; • — 240 800 3’3 * The word (< pyrites” has been used throughout to designate the sulphide FeS2 without prejudice as to its nature. From it« crystalline form it was evident that some of the material used in the last experiment was pyrites and not marcasite. Table II. (I) Description of coal. (2) Oxygen absorbed. (3) Carbon dioxide evolved. (4) Carbon dioxide evolved per 100 cubic centi- metres of oxygen absorbed. (5) Initial rate of absorption per hour. (6) Final rate of absorption per hour. (7) Final tempera- ture. Cubic < ubic Cubic Cubic Cubic Degs. Cent. centi- centi- centi- centi- centi- metres. metres. metres. metres. metres. Top softs, containing 43 per cent, of pyrites 321 118 37 54 55 51’2 Anthracite 132 0 0 59 32 49’4 Top coal 459 5’4 1’8 46 46 52’7 Bullhurst 60 0’4 0’6 11’2 7’7 47’2 Hard coal No. 1 195 2*7 1’3 18’6 22’0 50’0 Top softs .— 0’7 First part 534 3*6 186 — — Second part 1,041 20’8 2’0 — 189 66’4 Hard coal No. 2 i i,uo 12’1 1’0 90 78 62’5 Slack : i 31 0’02 * 0’06 14’0 13’7 46’0 Iron pyrites from coal i 240 102 43 475 — — tion of carbonaceous matter. Certain peculiarities of this experiment make the result rather less reliable than in the other cases. In order to find out to what extent the iron pyrites present in the coals had Undergone oxidation during the experiment, attempts were made to determine the amount of soluble sulphate (S04) present in the coal before and after the experiment. It was found impossible to get constant results unless the sulphate was dissolved out in an inert atmosphere with very dilute acid free from dissolved oxygen. Hydro- chloric acid diluted with freshly boiled water was allowed to act in an atmosphere of carbon dioxide, and the amount of sulphate was determined by the precipi- tation of barium sulphate. In some cases very little sulphate was found to be present in the coal after the oxidation experiment, so that the amount of sulphate produced during the experiment was exceedingly small, and in no way accountable for the heat evolution. Thus in the case of “ hard No. 1,” which contained 0’12 per cent, of iron, only 0 03 per cent, of soluble sulphate was present after the absorp- tion experiment. Even if the whole of this was formed during the experiment, it would account, as shown by equations below, for an absorption of only 32 cubic centimetres of oxygen, whilst 195 were actually absorbed. Determinations as accurate as possible were made in the case of “ top softs containing pyrites,” and it was found that the soluble sulphate present before the experiment was O’15, and after the experiment 0 40 per cent. Now the reaction accompanying the oxidation of pyrites is very probably the formation of ferrous and ferric sulphates with sulphuric acid, which latter acts upon the calcium carbonate present, giving off carbon dioxide. These reactions may be represented by the following equations: 4 Fe S2 + 2 H2 0 + 15 02 = 2 Fe2 (S04)s + 2 H2 S04; and 4 Fe S2 + 4H2O + 14 O2 =4Fe S04 + 4 H2 S04. There is little difference i i the amounts of oxygen required for the oxidation of pyrites according to these reactions. In the experiment quoted above from the amount of sulphate produced it would be expected from these equations that 319 and 298 cubic centimetres of oxygen respectively would be required. The value actually found was 321 cubic centimetres ; but it must be remembered that some oxygen would be expended in the oxidation of the carbonaceous matter. Other interesting and important facts concerning the oxidation of coal were obtained during the experiments, and the data on these points are collected in Table II. The third column of Table II. gives the volume of carbon dioxide developed during the oxidation, and for comparison with the oxygen absorbed at the same time the percentage ratio of these two quantities is given in column 4. As the duration of the experiments varied from about 4 to 24 hours, the initial and final rates of absorption of oxygen are given in columns 5 and 6, so that the speeds of the action for different coals can be readily compa red. The partial pressure of oxygen at the beginning of the experiment varied, with an average value near 0'75 atmosphere, and to make these initial rates comparable, corrections have been applied to give the initial rates in pure oxygen, assuming that the rate of reaction is proportional to the partial pressure of oxygen, similar corrections being applied to obtain the final rates. The initial temperature was always near 45 degs. Cent., and tfie final temperatures are given in column 7. From the values for the amount of carbon dioxide evolved, it is at once seen that the oxidation of the coals containing little pyrites gives very little of this gas, whilst large volumes are produced in the two experi- ments with material rich in pyrites. The carbonaceous matter, which includes some of the higher cyclic unsaturated hydrocarbons, is probably oxidised chiefly by the addition of oxygen to the complex molecules. It is interesting to note that in the experiment conducted quantitatively in two parts, the production of carbon dioxide is much greater in the latter part of the experiment. The large evolution of carbon dioxide was responsible for a curious phenomenon in the experiment with pyrites, a similar effect of much less degree being noticed in the experiment with “ top softs rich in pyrites.” The heat evolution when the pyrites was oxidised was at first very rapid, but quickly ceased, because, owing to the evolution of carbon dioxide, the further inflow of oxygen was largely prevented. The pressure of the gas at first fell considerably, but soon a minimum pressure was reached, and this fall gave place to a rise, owing to the evolution of carbon dioxide, and finally atmospheric pressure was slightly exceeded. Oxidation, therefore, almost ceased because the oxygen in the flask was exhausted, and none could enter to con- tinue the process. The taking of a sample at this stage admitted oxygen, which gave a fresh impulse to the reaction, and the temperature, which had become steady, again rose rapidly. Again the pressure curve showed a minimum pressure, owing to the evolution of carbon dioxide; and when a sample of gas was analysed the next morning, 15 hours later, it was found that the oxygen in contact with the pyrites had became reduced to 4*3 per cent. The greater part of the carbon dioxide was evolved after most of the oxygen absorption had taken place. It may be concluded from this that the carbon dioxide is produced as a result of a reaction brought about by the products of the oxidation of the pyrites. The evolu- tion of carbon dioxide is doubtless due to the action of sulphuric acid on limestone present in the pyrites. The sulphuric acid is formed by oxidation of the pyrites in the coal and by the hydrolysis of the sulphates of iron produced at the same time. If this hydrolysis was complete, and there was no retention of carbon dioxide in the form of basic iron carbonates, the volume of the gas evolved should be equal to about 55 per cent, of the oxygen absorbed. The carbon dioxide evolved in the pyrites experiment was some 43 per cent, of the volume of the oxygen absorbed, but the rise in pressure caused errors which could not be properly estimated. For the proper elucidation of the reactions occurring in the oxidation of pyrites, a modified method should be used, in which it is possible to remove and measure the carbon dioxide continually, so that there should always be plenty of oxygen in contact with the material to continue the oxidation. From the rates of absorption which are given in Table II., a valuable opinion may be formed of the relative extent to which these different varieties of coal would become heated when exposed in a finely-divided state to the oxygen of the air. The most rapid absorp- tion of oxygen occurred in the case of pyrites picked from coal, and the figure is a minimum value, because the evolution of carbon dioxide would probably begin early in the action. Owing to the low specific heat of pyrites (012), as compared with an average value of about 0 3 for the other samples of coal, a given evolution of heat produces a much greater rise in temperature in pyrites than in coal. Thus for pyrites the initial rise in temperature was over five times, but the initial rate of absorption of oxygen was only two and a-half times as great as in the case of the experiment with top softs. It will be noticed that the rate of absorption of oxygen for top softs containing 43 per cent, of pyrites is only about a ninth as great as in the case of nearly pure pyrites. Possibly this is due to differences in the structure or physical form of the pyrites, but there may also be chemical differences to account for this. In some experiments the proportion of oxygen in the flask became considerably diminished. Thus a£ the end of the pyrites experiment the gas contained only 4 3 per cent, of oxygen, whilst the proportions were 8 and 20 per cent, of oxygen respectively in the experi- ments with top softs and with top softs rich in pyrites. The corrected rates of absorption in the two last-named cases were slightly greater at the end than at the beginning of the experiment, but the temperature, was of course higher. It seems certain from these facts that the oxidation and heating of coaldust could not be prevented by any moderate reduction in the proportion of oxygen present in mine air. General Conclusions. 1. The heat which was evolved when coaldust was hested in an atmosphere rich in oxygen was nearly proportional to the volume of oxygen absorbed, the mean value being 3*4 calories of heat produced during the oxidation brought about by the absorption of 1 cubic centimetre of oxygen. 2. The production of heat may be attributed to two chemical changes—namely, the oxidation of iron pyrites and the oxidation of carbonaceous matter. 3. The oxidation of carbonaceous matter in coals practically free from iron was not so rapid as in those containing much iron, but continued for a long time, comparatively little carbon dioxide being evolved, so that eventually there was considerable heat evolution even in the absence of ventilation. 4. The oxidation of iron pyrites was at first very rapid, but soon almost ceased, because the flask became choked with carbon dioxide, which prevented further admission of oxygen. With conditions under which there is diffusion of air through the coaldust, and when a considerable amount of iron pyrites is present, the oxidation of this mineral would possibly be the pre- dominant factor in the spontaneous heating of coaldust. 5. Oxidation of coaldust takes place in contact with gas containing much less than the normal proportion of oxygen present in air. 6. The oxidation of carbonaceous matter and the total changes occurring in pyrites during the absorption of a given volume of oxygen produce about the same amount of heat, so that the rate at which heat is given off in the oxidation of coaldust due to either process may with surprising nearness be determined by the volume of oxygen absorbed. Partnerships Dissolved.—The London Gazette announces the dissolution of the following partnerships :—R. Dobson and H. Dobson, as electrical engineers, at Dean-road, Salford, under the style of R. and H. Dobson ; F. Ward and J. Clare, as brick and tile manufacturers at Burton Pedwardine and Sleaford, Lincolnshire, under the style of the Sleaford Brick and Tile Company; W. Bower and A. Sullivan, as coal merchants, at Colliery Offices, Grove-road, St. John’s Wood, London, under the style of the Consolidated Colliery Com- pany, so far as concerns W. Bower; W. Burgoine and A Burgoine, as engineers and millwrights, at Croft-street Foundry, Bury, Lancashire, in the name of John Burgoine and Sons; J. Ogden and J. C. Jackson, engineers and mill- wrights, Lansdowne Ironworks, Chadderton, under the style of Jackson and Ogden. Rescue Work in West Yorkshire.—A rescue scheme, on somewhat similar lines to that devised by South Midland coalowners, is being considered in West Yorkshire. It is hoped that the nucleus of the new scheme may be found in the West Riding Collieries Ambulance League. That organisation, with about 1,000 members, is doing excellent service for the mining community in providing instruction purely in ambulance work, the value of which is noticeable in the annual competitions. The present idea is to incor- porate rescue work with ambulance work in connection with that League. With the co-operation of the University authorities and the coalowners, it is proposed to form brigades in various centres the members of which would take a course of training at the Leeds University in rescue work, with different kinds of apparatus. Special attention has been given to rescue work by the Mining Department of the Leeds University during the past session. Mr. David Bowen, the acting head of the department, who has lectured not only in Leeds, but in many mining centres in West Yorkshire, has given some prominence to this aspect of a miner’s calling. Special classes for rescue work have also been held at the Univer- sity. Unfortunately, these have not been very well attended, the principal reason being that it is difficult to arouse sufficient enthusiasm among the miners to lead them to made periodical journeys to Leeds. Next session, how- ever, this point will not be lost sight of, and it is probable that arrangements will be made for holding classes in various mining centres. The Mining Department of the L-eds University at present owns only on« set of rescue apparatus—presented by the inventor, Dr. W. E. Garforth. Others have from time to time lent appliances of various types, and it is suggested that ooalowners would render a useful service by making a permanent gift of rescue appa- ratus to the department.