88 THE COLLIERY GUARDIAN. January 8, 1915. CURRENT SCIENCE. AND TECHNOLOGY. The Life of the American Coalfields. We are accustomed to think of the coalfields of the United States as not having passed as yet beyond the “ peascod ” stage; an exception being the anthracite fields of Pennsylvania, in which it is recognised that production has reached high-water mark. Some doubt was thrown upon this view by Mr. Carl Scbolz, in his presidential address at the recent American Mining Congress. Mr. Scholz has a wide experience of American coal mining, and he says he has often endeavoured to reconcile the statements published by the United States Geological Survey on the vast amount of coal coal available in certain fields with which he is quite familiar. He points out that these statements refer to all the coal in existence without distinguishing as to the cost of extraction; in fact, all Government reports are silent on this point, and the ordinary reader naturally believes that the billions of tons of coal available can be produced at no greater cost than the present supply. This cannot be true, and in less time than the average man believed, they would be forced, he said, to recognise the fact that even the largest coal fields are being exhausted very rapidly, and that the remaining coal, while available, will cost many times over the present cost of production. The average life of a coal mine in the United States rarely exceeds 25 years. In the major portion of the coal fields, particularly the interior sections, rarely more than two or three workable veins exist in the same territory, frequently only one. Mr. Scholz mentioned a few of the sections more generally known where the production has diminished, such as the northern coal field of Illinois and the Hocking Valley field of Ohio. In the Great Kanawha district of West Virginia, all of the coal along the river has been worked out or abandoned and the newer mines have been located along creeks and tributaries to the river. If these mines are worked out in as short a period as those along the river front, it will not take very many generations to exhaust the field. The Rand’s Largest Winding Engines. The following table gives particulars of the largest electrically-driven winding engines on the Hand. It was prepared by the South African Institute of Electric Engineers for the Association for the Advancement of Science:— Name of Mine. Name of Supplier. Type of Winder. No. of Winder Motors. H.P. of Winder Motors (continuous rating). Maximum Depth of Wind. Weight of Rock per Wind. No. of Com- plete Trips per hour. Voltage of Winder Motors. Speed of Winder Motors. Crown Mines Ltd. Electrical—G. E. C. of America (S.A. Gen. Elec. Co.) Mechanical ■—■ Eraser & Chalmers, Erith, Eng. Ward-Leonard cylindro-conical drums. 2 2,000 H.P. each motor. 3,540 ft. vertical. 8 tons. 44 1,000 v. across 2 motors in series. 53-5 r.p.m. Crown Mines Ltd. Motor generators— Siemens. Winder motors—A. E. G. Mechanical — Eraser & Chalmers, Erith, Eng. 2 Ward-Leonard winders cylindro-conical drums 4 (2 on each winder). 1,420 H.P, each motor. 2,260 ft. vertical. 8 tons. 45 1,000 v. across 2 motors in series. 53*5 r.p.m. East Rand Pro- prietary Mines Hercules shaft. Messrs. The British Westinghouse Electric & Manufact’g Co. Ltd. Ward-Leonard cylindro-conical drums. 2 750 H.P. each motor. 4,500 ft. vertical. 8 tons. 20 1,000 v. across 2 motors in series. 33-3 r.p.m. Village Deep Ltd. and City Deep Ltd. (6 similar equip- ments) . Messrs. The British Westinghouse Electric & Manufact’g- Co. Ltd. 3-phase motors direct-coupled 12 cylindrical drum hoists 4 Whiting hoists) 1 .1,600 H.P. 3,600 ft. vertical. 5 tons. 32 2,000 v.— 3-phase— 50 cycles per second. 100 r.p.m. Bantjes Consoli- dated Mines Ltd. Messrs. Siemens Ltd. 3-phase motor, geared to cylindrical drums. 1 1,470 H.P. 4,000 ft. incline. 5 tons. 23 2,000 v.— 3-phase— 50 cycles per second 250 r.p.m. Consolidated Lang- laagte Gold Mng. Co. Ltd. (2 similar equipments). Messrs. Siemens Ltd. W ard-Leonard 1 1,290 H.P. Compound shaft. 1,230 ft. vertical and hend 3,000 ft. incline. 5 tons. 23 500 v. direct current across winding motor. 80 r.p.m. N ew Modderf ontein Gold Mng. Co. Ltd. Messrs. A. E. G. Electrical Co. of S.A. Ltd. 3-phase motor, direct-coupled to cylindrical drums. 1 1,200 HP. 2,000 ft. 3 tons. 45 2,000 v.— 3-phase— 50 cycles per second Test of the Largest Air Compressor. A paper was read recently before the South African Institute of Engineers by G. M. Clark, detailing the official test of the large turbo-compressor used for delivering compressed air to the mines belonging to the Rand Mines Limited. In this plant air is delivered through a network of pipes 30 miles in length and varying in diameter from27i in. downwards to 20 points oE supply at a pressure of 100 to 110 pounds per square inch gauge pressure. The total capacity of these pipes is nearly 90 tons (of 2,0001b.) of air, and the power installed to drive the compressors is nearly 60,0u0 kw. The machine runs at 3,000 revolutions per minute, and is rated at 7,000 kw., on the turbine, and is one of three similar machines installed under the same contract. The low-pressure stage is next to the turbine, and is double ended. The air at atmospheric pressure is taken in at each end, and is discharged by a duct at the centre. This automatically balances the end thrust on this stage. From the first stage the air passes through the first intercooler, then through the second or inter- mediate stage, and then through the second intercooler, and, finally, through the high-pressure stage. All stages are wafer-jacketed, and water also circulates through the diaphragms. The compression that takes place in the first stage is from atmospheric pressure to about 0*8 atmosphere above, whilst the second stage raises the pressure to nearly 3 atmospheres, and the final stage to 9 atmospheres gauge pressure. The tempera- ture of the air entering the compressor is nearly 20 degs. Cent., with a rise to 80 degs. Cent, at the end of the first stage. It is again cooled to 30 degs. Cent, in the intercooler with circulating water at 20 degs. Cent., and leaves this stage at about 100 degs. Cent., after which it is again cooled to 35 degs. Cent, in the second inter- cooler, and finally rises to 90 degs. Cent, in the high- pressure stage. The isothermal compression is com- pleted by the final cooling in the pipe-line distribution system to the original atmospheric temperature of 20 degs. Cent. These temperatures and pressures vary with the load on the machine, but the above statement is nearly accurate for the full load of the machine. The tests that were carried out in August 1914 on the 5,000 air-kilowatt generator were officially for the purpose of deciding whether the guarantees were fulfilled. The power company does not sell air in terms of air-kilowatt hours as defined above, but in terms of air units, which are defined as 64T per cent, of an air-kilowatt hour. This fraction was introduced so that the selling price of an air unit and of an electric unit might be the same. This air unit represents approximately what the machine would have done had an electric generator been attached to the turbine instead of a compressor. The conclusion to be derived from the report on the tests is that, whilst a very great advance has been made in the size of turbo-compressors, this advance has been accompanied by another great advance in the science of design, so that the efficiency is now at least 10 per cent, above that of machines previously constructed by the same designers. From the figures obtained it is pro- bable that three-quarters of the energy of the steam is convertible into mechanical work on* the shaft of' the turbine, and of the work on the shaft two thirds can be utilised in. the isothermal compression of air with a compression ratio of nearly 12. Thus, on the whole, there has been an increase from a conversion of little more than 40 per cent, of the steam energy to prac- tically 50 per cent. The report incidentally shows that the orifice method of measuring air and water is capable oE being used with an accuracy equivalent to the com- mercial accuracy of electrical measurements. There is no doubt that measurements taken in this way are so accurate that to allow a tolerance of 2k per cent, for accuracy of measm ements is altogether too great. The report shows the facility with which steam measure- ments may be handled when the notion of the steam kilowatt is introduced, and the use of the Mollie r diagram when converted to read steam energy directly in kilowatt hours per pound of steam gives immensely increased power of thought in all questions of turbine economy as compared with the use of ordinary steam tables. The Value of Sand Filling. An unusual example of subsidence which occurred recently at the Village Main Reef seems to point to a merit of hydraulic packing which had not previously been suspected. For a considerable distance round the shaft at this mine no open areas exist, the whole space consisting of either sandfilled stopes or solid ground. It was the solid ground, however, which was affected by the recent rock movement, the suggested explanation being that the hanging wall had slowly subsided on to the packed sand until no further movement was possible ; on the other hand, the solid rock pillar would have reached a state of acute tension, which was disturbed by a general movement of the overlying strata. This was sufficient to burst away the sides of the pillar. The interesting point is that the area which could reasonably be regarded as the safest and strongest became under the circumstances the more dangerous and weaker. A subsequent inspection showed that the workings and drives in the sandfilled area were quite unaffected, no disturbance of the filling being detected Determination of Carbon Monoxide and its Physiological Action. In Bull. No. 92 of the Hygienic Laboratory of the Treasury Department, United States Public Health Service, A. Seidell and P. W. Meserve discuss the gaseous impurities in the air of railway tunnels. An interesting part of this paper is that which deals with the methods of determination of carbon monoxide, and the physiological action of this gas. The methods employed for the determination of carbon monoxide fall into three classes. First, absorption in an ammoniacal or a hydrochloric acid solution of cuprous chloride ; second, the physiological method based on the absorption of carbon monoxide by blood; third, the reaction of carbon monoxide with iodine pentoxide, according to which two atoms of iodine are liberated for each five molecules of carbon monoxide oxidised to carbon dioxide: 5 CO + 12 O5 — 5 CO2 + ?2. It is this last method which has been chiefly employed in analysis of mine air. The results showed that at a temperature of 150 degs. Cent, from 88 to 98 per cent, of the carbon monoxide present could be recognised in very dilute mixtures of this gas with air. A review is given of the literature upon the physiological effects of small amounts of carbon monoxide, and also sulphur dioxide, and it is concluded that the concentrations in air necessary to produce a recognisable harmful effect are somewhat .greater than 267 parts per million in the case of carbon monoxide, and 15T parts per million in the case of sulphur dioxide. As Dr. Haldane has shown, however, it is not only the concentration which tells in the case of carbon monoxide poisoning, but also the duration of contact with the blood. A 30 per cent, saturation of the haemoglobin in the blood of a man would require the absorption of 330 cubic centimetres of carbon monoxide, and the process being cumulative the time factor is of importance. Analysis of Coal with Phenol as a Solvent. A valuable contribution to the study of the composi- tion of coal has been published recently under the above title by the University of the Illinois Engineering Experiment Station (Bull. No. 76), the authors being S. W. Parr and H. F. Hadley. Of available solvents such as phenol, ortho-cresol, low boiling tar distillate, para-cresol, pyridine, phenol-toluene mixture, aniline, methyl aniline, acetone, toluene, benzene, carbon- disulphide and turpentine, the authors selected the first as being most efficient as a solvent of the resinous constituents of coal. Thus the attempt has been made in the work described in this bulletin to separate the coal substance without change oE chemical structure into two general subdivisions : the one representing the degradation products of the original cellulose material and the other representing the resinic or pitch-like bodies. With these subdivisions in hand it is possible to make, for example, a more detailed study of the conditions in one division which produce weathering and deterioration of coal, oxidation, and spontaneous combustion. The other portion offers a better oppor- tunity than has hitherto been available for studying the coking constituents and their behaviour under oxidation and distillation processes. The soluble material also serves as an index of the type of coal, differentiating between varieties of bituminous coal more minutely than is possible with a simple volatile matter determina- tion. In general it was found that the cellulose residuum has a more active avidity for oxygen than the resinic substance. Both types of material take on notable quantities of oxygen at 212 degs. Fahr., though the resinic substance may be heated to 350 degs. Fahr, in a non-oxidising atmosphere without decomposition or loss of volatile matter. It is interesting to compare the results of these experiments with those obtained by Messrs. Clark and Wheeler using the pyridine solvent. Whereas the latter found that the extracted matter was richer in methane and ethane than was the residue, Messrs. Parr and Hadley found that the phenol extract was poorer in methane but richer in hydrogen than the residue. It may, therefore, with reason be asked whether these different solvents do, as a matter of fact, extract the same part of the coal substance. Amongst the conclusions arrived at by the authors are the following:—The phenol extract varies widely in amount in different coals ; the coking constituent of the coal is the extract, the residue being non-coking ; the extract contains more volatile matter than the residue, but the gaseous products of destructive distilla- tion are nearly the same in composition in each case; oxidation of the coal decreases the amount of the phenol extract and diminishes the coking properties of the coal. The Origin of Coal Seams. There is still a diversity of opinion amongst geologists as to the exact conditions under which coal beds originated. While the vegetable origin of coal is generally accepted there is no agreement as to the conditions under which the coal measure vegetation grew and was accumulated. In this connection con- siderable interest attaches to the evidence afforded by the study of coal measure plants, which has recently been admirably summarised by Prof. A. C. Seward in a recent issue of the Quarterly Journal of the Royal Meteorological Society. Prof. Seward is of opinion that it is by no means unlikely that the atmosphere of the coal period was richer in carbon dioxide than it is