AuGrsT 1, 1887.] 



♦ KNOWLEDGE ♦ 



223 



4-|- miles each. The greatest length of a single coui-se wras 

 9.[L mUes. The total distance travelled was 70 miles. All 

 these quantities are now greatly increased in the larger 

 mines of the present day. As much as 300,000 cubic feet 

 per minute is in some ca^es supplied. 



Much ingenuity has been expended on the inyention of 

 huge air-pumps and fans for the ventilation of co.il mines. 

 Many have been patented, and a few actually used, rather 

 in small continental mines than in the lai'ger collieries of 

 this country. The steam-jet has also been applied. But 

 the most successful agent, the giant whose services can be 

 obtained at the smallest wage, is gravitation. The bunglers 

 of domestic ventilation seem to forget, or not to have 

 learned, that air is heavy, and becomes of itself a directly 

 available ventilating engine by its accommodating valuation 

 of weight in proportion to bulk. The simple principle upon 

 which colliery ventilation is conducted, and other ventilation 

 should be conducted, may be illustrated by the following 

 experiment. 



Place a few layers of paper on a table, and on this a 

 lamp-chimney — the use of the paper is to afford a cushion 

 on which the bottom of the chimney shall rest without air 

 space between it and the table. Then take a eandle-end 

 about an inch long, light it, and place it on the paper with 

 the chimney over it. In spite of the open top of the chim- 

 ney, the candle will be suffocated for lack of air — will flicker 

 and struggle, and finally become extinguished by its own 

 exhalations if the chimney is above six or eight inches high 

 and the candle is placed fairly in the middle of the chimney. 

 Repeat this more than once to prove that the extinction is 

 not accidental. 



Now cut a piece of metal (card will do if slightly 

 moistened and carefully used) of T shape, with the stem of 

 the T nearly as wide and long as the lamp-chimney, and 

 the cross top just sufficient to serve as a rest, so that the 

 broad stem may hang down and divide the tube into two 

 equal partitions, extending from the candle-wick upwards. 

 Jsow relight the candle and place the glass chimney thus 

 divided into two pai-titions over the candle as before. The 

 flame will presently take itself to one side or other of the 

 dividing partition, and, having once done so, wDl remain on 

 that side and burn freely, though occupying an apartment 

 with only half the air space of that in which it was pre- 

 viously smothered. 



If the experimenter is one of those wicked people who 

 smoke tobacco, a puff from his pipe or cigar directed to the 

 top of the divided chimney will demonstrate at once the 

 reason of the change. The smoke will be forcibly dragged 

 down that side on which the flame of the candle is not, will 

 turn rapidly round the lower edge of the partition, and then 

 rapidly ascend on the side in which the flame of the 

 candle is. 



The rationale of this is simple enough. When the chim- 

 ney is divided by the partition and without the candle 

 flame, there are two columns of air communicating below, 

 one on each side of the partition. So long as these are of 

 equal temperatiu-e, and consequently of equal weight, they 

 balance each other and remain at rest ; but when the candle 

 is lighted and its flame takes to one side or the other, that 

 side is heated and expanded. There is less air in a given 

 space on that than on the other side, and consequently the 

 heavier column presses up the lighter, which thus ascends 

 by virtue of the impulse given to it by the preponderating 

 gravitation of the cooler air in the other partition. 



When the chimney is undivided the candle-flame raises 

 all the air within it to a higher temperature than the outer 

 air, and therefore this denser outer air proceeds to sink 

 below the Hghter air ; but in doing so it encounters the 

 uprising heated air. A struggle ensues between the directly 



opposed currents in the confined space. The flame of the 

 candle indicates this very instructively. It has sunk down 

 nearly to extinction, when presently it starts up vigorously, 

 being blown aside at the same moment. This is when its 

 feeble heating power permitted a downcast of fresh air on 

 one side or other, but the greater this downca.^t, the greater 

 the uprising and consequent resistance to fresh downcast, 

 and thus, after a series of near approaches to death and 

 sudden revivals, the flame at last expires. 



The lamp chimney in this experiment represents the 

 shaft of a coalpit divided as coalpit shafts formerly were 

 divided in this country by a brattice, and as they ai-e still 

 divided in other countries where human life is held less 

 sacred than capital. I have already referred to the 

 accident which was mainly instrumental in bringing about 

 this legislation, but an interesting letter I have received 

 from a reader of Knowledge (who writes from Hetton-le- 

 Hole, and e\'idently understands what he is writing about) 

 tells me that I made a mistake in attributing the wreck of 

 the brattice to a .swing of the cage. As the catastrophe is 

 historical and instructive, and my mistake was derived 

 from a published account that must mislead othere, I will 

 quote the letter. Mr. iloon (or Jloor) says : " The real 

 cause of the melancholy accident (which took place on 

 January IG, 1862, causing the loss of 202 lives) was the 

 fracture of the cast-iron beam of the puniping-engine, and 

 the consequent precipitation of its outer end (weighing 

 about twenty-two tons) down the pit shaft. It carried 

 away the wooden brattice, pumps, and the pit work gener- 

 ally, and blocked up the shaft to a depth of about 138 

 yards from the surface, where the downward course of the 

 debris was arrested by the oak buntons on which the 

 middle set of pumps rested. Evei-j' effort was of course 

 made to rescue the imprisoned men, but it was found im- 

 possible, so great was the wreck, to clear the shaft in time, 

 and the result was that the whole of them succumbed to 

 suffocation by the carbonic acid gas." 



The death of these poor fellows by suffocation in spite of 

 the large space of main roads, cross roads, and workings, 

 demonstrates the absolute necessity of continuous and 

 sweeping ventilation. This disaster further proves the 

 terrible risk to which the whole population of a colliery is 

 exposed wherever there is but one shaft — one outlet. Any 

 accident whatever, and there are many that may occur, 

 which closes this one outlet or damages its hauling and 

 ventilating machinery, leaves them imprisoned in a dreadful 

 tomb, in a position to which no demands of trade or commerce 

 or other men's luxury should wilfully render them liable. 

 Therefore our legislature justly ordered that thenceforth no 

 colliery shall be worked with less than two shafts, so that if 

 one should be disabled, the other remains available for 

 escape. 



A second shaft being now compulsory, neither is bratticed, 

 and one is used for the descending, the other for ascending 

 cmTcnt, or, in technical language, one is a downcast, the 

 other an upcast shaft. 



In some cases it is possible to obtain a natural downcast 

 and a natural upcast without any artificial aid. This best 

 occiu's when the dip or slope of the coal-seam is in the con- 

 trary direction to that of the surface slope. It is possible 

 whenever they differ, but the greater the difference the 

 better. Let us suppose that the coal-seam is level and the 

 sm-face sloping, the required difference is obtainable by 

 sinking two shafts down to the coal — one where the coal 

 is nearest to the surface, and the other where it is much 

 deeper. Thus we should have two shafts of unequal depths, 

 and consequently bearing columns of air of unequal 

 heights. 



In workings of moderate depth the underground tern- 



