1845.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



117 



in tlic mine ! but that is not all wliicli occurs llierc, for, in my Iwlief, by far 

 the greatest portion of combustible matter burnt in a mine, upon such occa- 

 sions, is the coal-dust which rushes up the passages when the explosion has 

 happened. When we went down, we found, near to the place where the ex- 

 plosion occurred, all (he columns plastered wilh coal-dust taken up from the 

 door and driven forward by the blast, forming a fiery stream passing Ihroush 

 the passages, part of it coking, other portions being converted inio gas, and 

 some cemented to the walls ; clearly showing the direction which the explo- 

 sion Iiad taken, because one side was plastered half an inch thick, while ihere 

 was none on the other side, indicating fully both the chemical and mechanical 

 eliects of the explosion. If I take a little coal-dust, and mix it with tliat 

 (lame, you will soon see what a difference there will be in the combination. 

 The danger arises not merely from the combination of air and fire-damp, but 

 from the kind of mixture wiiich I am now going to make. I have thrown a 

 little powdered coal Into this apparatus, and you see how much stronger the 

 combustion comes on. The gas. first of all, commences the evil, and then 

 lights up tills combustible matter (the dust of coal), of «liich the whole place 

 consists ; fioor, roof, walls, and every part being composed of it. The fire 

 thus gathers energy, and goes on ramifying through the mine. It is only 

 upon this principle that we can account for the extraordinary extent of injury 

 by choke-damp, the result of combustion, causing ninety-five deaths in what 

 was considered a very safe mine. 



Now, with regard to the coal gas; fori must re.ally shorten my observa- 

 tions for the purpose of bringing you at once to the point in relation to the 

 goaf and the coal-damp. Fire-damp is light ; and we may very well use an 

 experiment or two here, for the purpose of pointing out liy coal gas what its 

 cfTect is. Coal gas is really, in many rases, when made in London, not far 

 off in its degree of gravity from the fire-damp. Now, here you would not 

 understand in a moment the principle, but these experiments and demonstra- 

 tions make it far more impressive to the mind, (The lecturer then showed 

 various experiments, to prove that coal gas, and therefore the gas of the 

 miner, if accumulated under a vessel, or chamber open below, but having no 

 outlet above, would remain at the upper part, and when mi.teJ with atmos- 

 pheric air would, if a light be brought near, ignite and explode.) The conse- 

 quence is this, that if the blower, or any gas in the blower, can get into a 

 place of this sort, it will remain there some time. I will not put a light there, 

 because it might shake the thing to pieces. If I come here two, three, five, 

 or even ten minutes, after 1 have filled it with gas, I sh:ill find the fire-damp 

 remaining tliere. (Experimenting.) There it is. You jierceive that I had to 

 carry my light up a certain distance; I could not find it lower down, tut 

 there we found it. because of its lightness. So light is tliis gas and this fire- 

 damp, that it files from one thing to the other. I have one very important 

 point to show you wilh regard to tlie operation of these coming immediately 

 into action in the goaf. This gas is always to be found at the upper part of 

 any cavity where it may exist. If you will allow me to consider this as a 

 model goaf, (an oblong inverted vessel), for the purposes of our illustration, 

 you will soon see the effect of its lightness in determining thegas to one place 

 or the other ; for if I let a little gas into this goaf, which I can do from 

 this jet, whichever end of this goaf I incline up there the gas will be found : 

 it will not remain in one place, but will oscillate from side to side, according 

 to the position of the vessel, in consequence of its lightness ; being, in that 

 respect, comparable, in an inverse ratio, to water, which, of course, will How 

 from side to side in the vessel, because of its heaviness. Whatever you can 

 imagine in fluids you may suppose also in regard to gas. 1 will let gas into 

 this goaf. Although I have a great number of drafts, and I myself make a 

 considerable motion in the air, I dare say in this place we shall be able to 

 make the experiment. (The lecturer then shewed by experiment that the gas 

 was at all times in the upper part of the inverted vessel, and that it moved 

 from end to end, according as one or other end was raised.) 



In a mine, there appears to be a tendency to the evolution of this light 

 hydro-carburet fire-damp. It seems to be oddly given forth at times. A 

 man will come upon the blower, and enter a little cavity ; then there comes a 

 rush of gas from a place the size of my finger, rushing out, perhaps, and 

 taking fire by his candle : If it happens without any serious injury to the m:in, 

 it will burn away like a great torch. At other times it will creep up to every 

 part of the coal ; then an accumulation will take place wilh the atmosphere 

 from these blowers, but still equally dangerous. There was a case In which 

 the gradual evolution of fire-damp from the coal produced this oliect. A 

 vessel, laden with coal, having come part of Its voyage, the gas fnmi the cargo 

 came out and made the Iiold of the vessel explosive : a sailor hapin'ned to go 

 down below with a light, and the place blew uji, exactly in the same manner 

 as the explosions take place in these passages of the mines. This shows under 

 what circumstances the gas comes out of the coal during the working of a 

 mine. If there be any evolution of gas in a mine, which at any time causes 

 the conveyance of gas into a cavity of the goaf, it will, as you have seen in 

 tills experiment, tend to rise to the upper part. It is a light gas; every mix- 

 ture of it is lighter than .■ur, and the light gas will tend to rise to the higher 

 part. There is, therefore, every reason to believe, that if this goaf opened 

 into an upper stratum, and you will find there arc five, si.x, or more strata 



above that which they work in reality, from the opening of small seams and 

 beds, or whatever cause it be, it will open passages from that to the upper 

 strata of tills, to the fire-damp contrincd in the goaf itself. There is 

 not the least doubt that any vents of this sort would tend to become 

 resting-places for the gas, which would run into it at different times 

 and under different circumstances, and there remain in larger or smaller 

 degrees. There can be no doubt that the goaf is a very convenient place for 

 the gas to accumulate in ; that there is a tendency to that in the goaf from 

 the ventilation, the arrangement of which I must not go into, but It is very 

 beautiful. There are two deep pits ; tlie one lias a furnace at the bottom, so 

 that the first becomes a chimney. There Is an Immense draft up this pit, and 

 there is a great mixture of air and gas. They ventilate most carefully the 

 space of coal where they are working, because there they are ever coming to 

 new reservoirs of gas, and new apertures open into it. They ventilate the goaf 

 also, in some degree, but so feebly, that the air there is almost stagnant. 

 They cannot afford to have a sweeping current all over the w hole of the mine. 

 Whenever a mine contains 100 acres, any quantity of air whicii goes down a 

 cavity 12 ft. diameter cannot be made to extend over the wh<de of that space. 

 The gas goes through the apertures which are left ; so that in such places 

 the air must be regarded as really stagnant. Much more are the cavities 

 within the goafs stagnant. These goafs ar» loose masses of rocks falling 

 together. If you take a sponge in a gale of wind, the air sweeps away all 

 from the outside; It would not touch the cells, or inner side. These cavities 

 then become, in fact, reservoirs for fire-damp, if they have access to the goaf 

 It will contain fire-damp just as well as any other part. Any previous part 

 of the goaf may be made subject to fire-damp, if there is any in the goaf of 

 the mine. 



Now let us look at the effect of the goaf under certain circumstances. First 

 of all, if It be no generator, it opens to one place where the fire-damp is 

 evolved ; but we lliink it does evolve it. There Is plenty of proof that the 

 goaf is a very dangerous place. Not many weeks after we came away an ac- 

 cident happened. A man put his candle up a cavity of a goaf, and said, 

 " Sec, here is no damp here !" when an explosion immediately took place, and 

 four men were killed, proving, very unfortunately for the men themselves, 

 that the goaf is a very dangerous place. Whether the fire-damp is evolved 

 there or not we cannot positively say ; but if not, it is quite clear that any 

 gas evolved in any part of the coal in excess will gradually creep into the 

 goaf. There are certain mines, we were informed, which to this day are in- 

 volved in this condition ; although they ventilate carefully, as well as they 

 can, all through the mine, still they are obliged to adopt regular periods for 

 firing the residue of the mine, " firing ofi," as they call it, for the purpose of 

 clearing away, by burning, the fire-damp. Sometimes they are obliged to do 

 this three times a-day for the purpose of getting rid of the fire-damp. Such 

 gas as that, however, must always be dangerous. The goaf, therefore, is 

 pi?rpetually liable to be a reservoir of gas, even though it may not itself be a 

 liroJucer. If there be any gas in the goafs, it will be in the upper parts. If 

 there be any cause which may increase the quantity of gas in the goaf, or 

 lead to any further influx of it into the goaf, it will flow off at the upper part. 

 There are some very extraordinary causes which tend to make the gas ascend. 

 First of all, bear in mind what I told you before of the manner in which the 

 men proceed in working the mine, taking away pillar after pillar, and then at 

 last, drawing the juds. Imagine a pillar here ; he props the roof up ; takes 

 away the pillar, and so converts it into a jud ; at last he withdraws the jud 

 and then what happens ? Part of the roof falls down, and extends the goaf, 

 But mark the consequence ; it will not merely have made the goaf larger by. 

 spreading the basin yet more, but the edge of the basin becomes a little higher. 

 Now, supposing a goaf of thirteen acres to be full of gas, or an explosive 

 mixture, down to a certain level, that the ventilation had carried off all the 

 gas up to that point. This breaking in of the goaf has the eflijct at once of 

 altering the level one foot. Throughout the whole extent of that goaf a 

 stratum of air in the interstices would pass ofl' one foot in depth, flowing out at 

 that one place. The whole of the adjustment of the a;rlal strata in that goaf 

 would be altered in that maner, just as though if you were break ofl' one foot 

 of the edge of a pond of water, you would let out one foot of its deplli. This 

 Is a very serious matter. 



There is, liowever, one other point which I must notice, and that an ex- 

 traordinary one, namely, the effect of the pressure of the atmosphere. The 

 philosophy is very well known to scientific men, though not generally under- 

 stood. Tlie atmosphere will vary as much as 3 in. in the barometer, fluc- 

 tuating from 28 to 31 in. in its weight, It often happens in a single day, 

 that it will drop one inch, falling from 30 to 29. What do you think would 

 occur in a goaf of that size, a small one. If the barometer descended to that 

 extent in one day ? The enormous quantity of air in the goaf, equal to the 

 bulk of Jcoal taken out, would expand, and occupy a larger space ; then, of 

 course it would overflow at the upper edge of the goaf in proportion to the 

 fill of the barometer. The gas becomes squeezed by the superincumbent at- 

 mosphere into every crack. It retreats into the solid coal itself; into the 

 cells of tlie coal ; the blowers all cease in some degree, orjdiminish in action. 

 Tlie air in the goaf retreats up, and takes a smaller space; fresh air is pourej 



16 



