April, 1915. 



KNOWLEDGE. 



105 



in a well-ventilated mine is continually absorbed 

 by the fine coal dust, whilst the neighbouring air 

 does not become stale. This combination is very 

 dangerous. Dr. Harger, at Liverpool, consequently 

 suggested " a small reduction in the percentage of 

 oxygen, and the addition of a little carbon dioxide 

 to such an extent as not to be harmful to respira- 

 tion, and to render coal-dust ignition impossible." 

 He further advised the introduction into the mine 

 atmosphere of flue gases, purified from harmful 

 gases and smoke. " It would," he said, " provide 

 immunity, not only from coal-dust explosion, but 

 from fire-damp explosions, and as regards respiration 

 would be as good as ordinary air, and for people 

 liable to consumption better." But the miner does 

 not relish the idea. 



Possible dangers of firing fire-damp, or coal dust, 

 are : ( I ) Lamps of all descriptions ; (2) electric 

 leakage causing a spark ; (3) blasting explosives ; 

 whilst it is advisable that fire-damp should not 

 accumulate. Professor Thornton has investigated 

 the danger derived from electric sparking. Messrs. 

 Sellars and Campbell, at Manchester, have studied 

 explosions of coal gas and air in the laboratory ; 

 but perhaps the most practicable investigations 

 are those employing incombustible dusts as a 

 means of " quenching " any likelihood of the 

 spreading of fire by coal dust. Mr. William Gar- 

 forth, at. Altoft, and Professor Dixon (by Ryalo 

 Commission), at Eskmeals, are diligently pursuing 

 inquiries in this direction. Bicarbonate of soda 

 and stone dust have been found most efficient ; 

 but the fact still remains that these mineral 

 irritants, if inhaled, encourage pulmonary diseases. 

 It is possible, however, to minimise this, and 

 consequently this does not constitute a serious 

 objection. Owing to the continual accumulation 

 of coal dust the stone dust, and so on, must also 

 be replenished from time to time. The idea of 

 keeping the inflammable dust constantly wet in 

 order to render it safe is attended with the serious 

 objection that the miner would have to work under 

 very unhealthy conditions. It must be remembered 

 that the dust must be continually swamped to 

 prevent drying up ; a state of affairs much worse 

 than before, since spontaneous combustion is 

 rendered more likely, especially if any sulphide be 

 in close proximity. 



Referring to dust which accumulates in flour mills 

 and oil-cake works, Dr. Harger said that ordinary 

 flour mills were on much the same plane as powder 

 magazines. To test this in a small way we only 

 need to enter a flour mill where the cleaner is 

 sweeping the floors, and to see the disturbed dust 

 ignite at some burning gas-jet and endeavour to 

 spread over the whole room. Measurements have 

 shown us that flour dust is much more explosive 

 than coal dust. Even bits of iron, when over- 

 heated by friction, are capable of inflaming this 

 highly explosive dust, and thus magnetic screens 

 are now employed to attract any stray bits of iron 

 which may be present. 



Attempts are being made to utilise coal dust 

 owing to its high calorific value, and it is very 

 probable that it will some day be used to a larger 

 extent. Present-day methods of blowing the dust 

 into furnaces are unsuccessful. 



The smoke nuisance dates as far back as Elizabeth, 

 whilst attempts at abatement have been made by 

 J. Watt (1785) and Cutler (1815). The causes are 

 traced to imperfect combustion, due to (a) inade- 

 quate supply of air, and (b) wrong combustion 

 temperature. Smoke in itself is not very harmful, 

 but the sulphuric acid produced from the sulphur 

 in the coal is very injurious, having a very corrosive 

 action, and unfortunately it cannot be eliminated by 

 the various methods adopted for smoke abatement. 

 The study of rain in different places suggests a 

 method of determining qualitatively and quantita- 

 tively the constitution of atmospheric pollution. 

 Tests with country and town rains show that town 

 rain is acid, whilst country rain is neutral. Anthra- 

 cite stoves are a successful attempt at decreasing the 

 smoke nuisance, whilst experiments are being made 

 with liquid fuel and electricity. Perhaps in the 

 future smoke will be a thing of the past, if Sir 

 William Ramsay's dream comes true, in which our 

 coal will be burned underground and electrical 

 energy stored up at the coalfields. At present, 

 however, the housekeeper can help by using gas- 

 stoves, although they are not very healthy. 



The factory, especially so in copper smelting, is 

 very wasteful. Taking the case of copper smelting, 

 a large quantity of metal dust, together with arsenic, 

 is thrown out with the smelter smoke, having dis- 

 astrous effects on the countryside. Long flues 

 have been found to recover a large quantity of 

 metal, but electrical methods are now employed 

 to better advantage. 



Sir Oliver Lodge in 1884 showed an experiment 

 at the British Association meeting in Montreal 

 in which smoke was caused to condense and fall in 

 fine particles by electrical means. By a similar 

 process he managed to clear from fog a space of 

 from fifty to sixty yards radius at Liverpool 

 University, the potential employed being one 

 hundred thousand volts, dense fogs being dissipated 

 quicker than light ones. This has been applied 

 recently to smelter smoke, and as much as ninety 

 per cent, of the metal dust can be recovered. The 

 commercial value "1 dust is only just beginning to 

 be realised. Wool dust, foi example, is now being 

 employed as a fertiliser. In the near future will 

 it be possible to collect road dust in order to extract 

 the rubber worn from motor tyres, and for it to be 

 profitable ? 



To phenomena dependent on dust must be added 

 crystallisation and supersaturation — the former 

 needing its presence, and the latter needing its 

 absence. 



And what would our world appear like if there 



no dust ? Very probably the sky would 



not have its delicate blue colour, but would be 



black, with the Sun glaring down on the Earth 



