Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/478

Rh 460 MINING [VENTILATION. uncommon. This gas is likewise given off in the Sicilian sulphur mines, where also the highly poisonous sulphuretted hydrogen is of frequent occurrence, the water in the work ings being often saturated with it. Small quantities of mercurial vapour occur in quicksilver mines. Products Such then are the principal gases which naturally pollute of respi- ^hg atmosphere of mines, and have to be swept out by ven tilation. In addition to these we have the products of the respiration of the men and animals in the pit, and those due to the combustion of candles or lamps, and the explosion of gunpowder, dynamite, &c. Dr Angus Smith 1 reckons that two men working eight hours, and using Ib of candles and 12 oz. of gunpowder, produce 25 392 cubic feet of carbonic acid (anhydride) at 70 F., viz., 10 &quot;32 by breathing, 12 276 by candles, and 2796 by gunpowder. The products of the explosion of gunpowder have been carefully studied by Captain Noble and Sir Frederick Abel, and the follow ing figures, showing proportions by weight, are copied from the valuable paper 2 containing the results of some of their researches: Curtis &amp;lt;fe Harvey s No. 6 Gunpowder. Mining Powder. Total solid products 57-74 47-04 Total gaseous products 41-09 51-35 Water 1-17 1-61 100-00 100-00 Curtis &amp;lt;fc Harvey, No. 6. Mining Powder. Carbonic anhydride 50-22 32 15 7 52 33-75 34-46 19-03 Sulphuretted hydrogen 2-08 7 10 2 4S 2 73 3-26 5 24 100-00 100-00 The volume (calculated for a temperature of C. and barometer 760 mm. of mercury) of permanent gases generated by the explosion of 1 gramme of dry powder is Curtis & Harvey, No. 6 241-0 cubic centimetres. Mining 360 3 ,, ,. MM. Sarrau and Vieille have communicated to the Academy of Sciences 3 the results of their researches concerning the decomposi tion of certain explosives, and more particularly gun-cotton and nitrated gun-cotton. The following table shows, in litres, the volume (at C, and 760 mm. of mercury) of each of the gases per kilogramme of the substance exploded in a closed vessel : Kind of Explosive. CO. C0 2. H. N. 0. C 2 H 4. US. Total. Pure gun-cotton 914 234 Ififi 107 741 G un -cotton and nitrate of } potash (50 per cent, of V each) i 171 109 45 325 Gun-cotton (40 per cent.)} and nitrate of ammonia &amp;gt; (60 per cent.) j 184 211 6 401 Xitro-glvcerin 295 147 ?n 467 Ordinary blasting powder 64 150 4 65 4 17 304 If, however, the explosive is decomposed at a pressure approach ing that of the atmosphere, the volumes (again at C. and 760 mm. of mercury) are very different, as shown below: Kind of Explosive. N0 2 CO. C0 2. H. N. C 2 H Total. Pure gun-cotton 139 237 104 45 33 7 565 Gun-cotion and nitrate of) potash (50 per cent, of each) j 71 68 57 3 7 196 Gun-cotton (40 per cent.) and nitrate of ammonia (60 per &amp;gt; 122 65 103 12 112 414 cent.) j Nitio-glyccrin 218 162 58 7 g I 452 When explosives are decomposed in this way they liberate nitric 1 Report of the Commissioners Appointed to Inquire into the Condi tion of all Mines in Great Britain to which the Provisions of the Act 23 tfc 24 Viet. c. 151 do not apply, Appendix B., p. 224. &quot;On Fired Gunpowder,&quot; Captain Noble and Mr F. A. Abel, Phil. Trans., 1880, p. 278. &quot; Recherches experimentales sur la decomposition de quelques explosifs en vase clos ; composition des gaz formes,&quot; Comptes Rendus 1880, pp.1058 and 1112. The solid residue of the mining powder consisted mainly of potassium carbonate, potassium monosulphide, and sulphur. The percentage composition by volume of the gas produced was : oxide and carbonic oxide, and the analyses of MM. Sarrau and Vieille confirm the practical experience of miners, who complain greatly of noxious fumes when, owing perhaps to a bad detonator, a charge of dynamite or tonite fails to explode properly. The air of mines is finally deteriorated by organic matter con tained in the exhalations of the men and animals employed and in the products of decaying timber, by dust, and by the solid par ticles constituting the smoke of explosives. It must be recollected also that the injury to the air is not confined to the addition of the gases and substances just mentioned ; but the proportion of oxygen is diminished by the combustion of candles, by respiration, the decay of timber, and decomposition of some minerals such as iron pyrites. Dr Angus Smith 4 sums up the results of his analyses of the air of British metal-mines as follows : Percentage by volume. Oxygen, average of 339 specimens 20-26 of ends 20-18 other parts 20 32 in currents 20-65 in large cavities 20-71 just under shafts 20-42 in sumps 20-14 Carbonic acid 0-785 He considers air with 20 - 9 per cent, oxygen as normal, and air with proportions between that and 20 6 as impure; and where the per centage of oxygen descends below 20 6 he calls the air exceedingly bad. According to these standards, only 10 67 per cent, of the samples showed the air to be normal or nearly so ; 24 69 per cent, were decidedly impure; whilst 64 63 per cent, or nearly two-thirds of the samples were exceedingly bad. The amount of oxygen in one specimen was as low as 18 52 per cent., whilst the carbonic acid often exceeded 1 per cent, and in several instances 2 per cent. It is evident that twenty years ago the ventilation of British metal mines was anythin room for improvement. but satisfactory, and even now there is Having explained the reasons why the air of mines must be constantly renewed, we must now point out how this desirable end is effected. Two systems are employed, natural ventilation and System artificial ventilation ; but, as both systems have been of vent described (COAL, vol. vi. p. 70), little remains to be said latlon - here, especially as the ventilating machines in metalliferous mines generally cannot for one moment be compared with the powerful appliances employed in collieries. In vein- mining there are generally many more shafts than in collieries, and natural currents are set up which are often considered sufficient for ventilating the mines ; never theless, the advanced workings, such as the ends, rises, and winzes, in fact all workings in the form of a cul-de- sac, are likely to require special means of ventilation as soon as they proceed a little distance from the main air -current. The means of ventilating a drift or heading are various. If a natural or artificial draught exists at the mouth of the drift, it may be diverted by an up right partition (brattice), or an air-way may be constructed along the roof or floor by a horizontal partition of planks (air-sollar) (fig. 89). secured at the end or fore-breast. Fig. 89. In this way a sufficient supply is The water -blast is another simple appliance ; it is pre cisely the same as the well-known tromp, and it blows a current of air through square pipes made of boards, or better through cylindri- cal pipes of sheet zinc. Fig. 90. The fall of water may be applied by Williams s water-jet, shown in fig. 90. The jet of water acts like an injector, and creates a powerful current. Small fans driven by boys, or better by small water- wheels or other machinery, are frequently applied, and the 4 Op. cit., p. 222.