October 1, 1895.] 



KNOWLEDGE 



225 



have attracted attention ever since the early part of the 

 seventeenth century, whilst the recognition of coal dust as 

 a significant factor in coal mine catastrophes is of 

 comparatively recent date. 



Fire-damp explosions were the first to receive the 

 attention of a scientific society, and there is a record of a 

 gas explosion in a mine in the Philosophical Transactions 

 of the Royal Society in the year 1677. 



At that period, however, miners generally ascribed the 

 presence of noxious gases in mines to supernatural agencies, 

 and strange and remarkable papers appeared from time to 

 time in various journals on the subject. As one result of 

 these inquiries, it became known that the tire-damp explo- 

 sion was caused by a flame coming in contact with the 

 mine gas. As it was impossible to work in a coal mine 

 without light, either some means had to be found to get 

 rid of the gas in fiery mines, or the mine had to be 

 abandoned. One method adopted was to draw air from 

 the surface to take the place of the dangerous air. Thus 

 we find, as early as the middle of the seventeenth century, 

 that a fire in a special air shaft was used for this purpose. 

 The air became rarefied in this shaft, and so upset the 

 equiUbrium that existed, the denser air in the working 

 shaft ran down into the mine, sweeping the gas -laden air of 

 the mine before it, and forced it into the air shaft, where 

 it, in its turn, became rarefied and found its way upwards 

 to the open air. This method of dealing with fire-damp is 

 still in use in some mines, but, instead of a mere fire, 

 furnaces are employed as the source of heat, and pre- 

 cautions are taken to prevent any explosive air from the 

 mine becoming ignited, and so causing disaster. Later 

 on, the idea suggested itself of destroying the fire-damp by 

 burning — a practice still in vogue in some few places ; 

 whilst, during the latter half of the eighteenth century, 

 chemical means were suggested for achieving the same 

 object. 



But about this period Spedding had discovered that fire- 

 damp really did not catch alight so readily as had been 

 supposed ; that, in fact, the temperature at which it 

 ignited was relatively high, actual flame being required to 

 ignite it, and mere red heat being insufficient for the 

 purpose. Up to this time we have seen that the treatment 

 of the fire-damp question was restricted to the elimination 

 of the fire-damp, and that no attention had been paid to 

 the character of the light employed. This discovery of 

 Spedding opened up a new field, and led to the invention 

 and introduction of his steel mill, which is illustrated 

 in the next column. 



It consisted of a metal framework carrying a steel disc, 

 which was mounted on a horizontal axis, having attached 

 to it a pinion, whilst a spur-wheel was mounted on a 

 second horizontal axis so as to engage the pinion. The 

 spur wheel was set in motion by a cranked handle, and 

 caused the rapid revolution of the steel disc, against 

 which a piece of flint was closely held, and the shower of 

 sparks thus produced provided the illumination, which was 

 intended to be of sufficiently low temperature to prevent 

 the ignition of fire-damp. This light, however, proved 

 feeble and fitful, and by no means safe. But attention 

 had now been drawn to the advantage of employing some 

 means of preventing the ignition of fire-damp. Hence it is 

 we find lamps introduced by Humboldt in 1796, and Clanny 

 in 1806, in which the air necessary for supporting the 

 combustion of a candle or oil flame had to bubble through 

 a layer of liquid on its way to the flame, thus isolating 

 the flame from the air in the mine. In some other lamps, 

 also, the products of combustion had to pass through a 

 layer of liquid. 



Such lamps, however, were awkward to manipulate. 



cumbersome and unsuitable for coal mining, and although 

 this was a move in the right direction, yet a satisfactory 

 means of illumination, coupled with non-ignition of the 

 fire-damp, had not been discovered. The question of the 

 ignition of the fire-damp was, however, soon attacked by 

 Sir Humphry Davy from another point of view — that is, as 

 to the circumstances attending an explosive ignition. It 



The Steel MiU. 



was he who found that the fire-damp alone would ignite 

 without explosion, and that even when mixed with varying 

 proportions of air up to eighty-five per cent., it did not give 

 rise to explosion, whilst with more air it became explosive, 

 increasing in violence as the percentage of air became 

 greater, until the air constituted eighty-nine per cent, of 

 the mixture, but fi'om this point onwards the explosiveness 

 of the mixture dimmished until it contained ninety-four 

 and a quarter per cent, of air, when it again ceased to be 

 explosive, and with larger proportions of air either burnt 

 quietly or not at all. The most dangerous proportions he 

 found to be eleven to twelve per cent, of fire-damp. 



It now became generally admitted that gas explosions 

 in mines were due to air containing from about five to 

 fifteen per cent, of fire-damp becoming ignited by contact 

 with flame or intensely heated gas, and thenceforth the 

 question, which had hitherto been treated in a haphazard 

 manner, could be dealc with in a rational way. Two 

 problems were thus presented for solution. 



Firstly, how to dilute the treacherous atmosphere of a 

 mine below the dangerous limit, and secondly, how to 

 light the mine without running the risk of igniting the 

 gas. These problems alone have furnished an inexhaustible 

 supply of work for the investigator and inventor. 



The method of treating the first of these problems was 

 to induce more external air to enter and circulate through 

 the mine, and this led to the introduction of various 

 means to supplant the furnaces already alluded to, and 

 we find steam jets, piston air pumps, rotary air pumps, etc., 

 employed in their turns with varying degrees of success. 

 At the present time fans are the means almost universally 

 adopted for forcing in, or drawing through, the coal mine 

 the requisite quantity of air for keeping the atmosphere 

 below the dangerous limit of combustibiUly. 



It is sufficient to note here that these fans have betn 



