SMOKE

(Low Germ, sniuke.) Smoke has been de fined as the visible effluvium or sensible exhalation of anything burning. The term is commonly applied to those results of the combustion or ignition of pit coal which escape from chimneys, and which constitute a serious and well-known evil and nuisance in large towns, manufacturing districts, and almost everywhere where large quantities of coal are consumed. Coal is often a very complex substance; but, putting aside its occasional and adventitious ingredients, carbon, hydrogen, nitrogen, and oxygen may be regarded as its ordinary and e ential constituents; and the results of its perfect combustion would therefore be carbonic acid, steam, and nitrogen. These substances would constitute invisible and incombustible gases and vapour, and would therefore escape from the chimney top, and blend with the atmosphere, without being perceived. But it unfortunately happens that from the way in which coaris burned its combustion is far from being perfect, and that besides the above-mentioned products inflammable gases and vapours, together with large quantities of very finely divided carbon, constituting soot and black and brown smoke, are vomited forth from the chimney shaft, not only contaminating the air, and making all neighbouring objects black and dirty, but also occasioning great lo of fuel; so that the smoke of London is not only a nuisance, but a very expensive one, and ought to be put down by legislative enactments, several of which have been from time to time suggested, but unfortunately never enforced, and are at this moment a mere dead letter. The neglect which this subject has encountered has arisen chiefly out of the difficulty of enforcing and inculcating rational doctrines upon the subject of combustion, and of getting persons to adopt new systems of construction in regard to furnaces and fire-places, new methods of stoking and managing the fire, and new kinds of fuel; and it is astonishing to observe the obstinacy and perversene which prevail in these respects amongst the masters as well as the men. There is another cause too, which no doubt has had its influence in retarding the adoption of means for diminishing the smoke nuisance, which is, the shoals of quacks and ignorant empyrics and impostors who have embarked in these speculations; so that till stringent and coercive measures are adopted in regard to it, founded upon scientific and rational principles, we must be content to continue breathing a tainted air, which fouls the organs of respiration, encrusts our buildings, and covers our books, pictures, and every article of furniture with an enamel of soot, and which dims the atmosphere to such an extent as materially to shorten the duration of metropolitan daylight That all these evils may be got rid of admits of no doubt, and ultimately with economy and convenience; though the first introduction of the remedies will probably be attended by many practical difficulties, and considerable inconvenience and expense. One remedy, and the most obvious, consists in the substitution of coke, anthracite, and certain other smokele fuel, for the bituminous and eminently smoke-generating varieties of coal now in common use. Another is, the construction of fireplaces and furnaces which shall not indeed burn smoke, but prevant its formation.It must be allowed that there are many practical difficulties in the way, rather perhaps of the application than of the invention or perfection of these contrivances; but experience has shown that none of these are of such a nature or magnitude that they may not be overcome by perseverance and skill. They all merge into one common principle, that of mixing air with the combustible vapours and gases generated by the action of heat on pit coal, so that by virtue of a due supply of oxygen they may be made to burn with flame, and become entirely converted into incombustible and transparent invisible vapours and gases, instead of being, as they now are, only partially burned, by which their carbon is precipitated, and escapes, together with the other imperfectly consumed matters, into the air. The foundation of a practical inquiry into the subject of the prevention of smoke has been laid by Mr. C. VV. Williams of Liverpool (E ays on the Combustion of Coal and Pre vention of Smoke). The theoretical details are e entially blended with the whole doctrine of heal; but the investigations w-hich most e entially bear upon them will be found in Sir H. Davy's Researches into the Philosophy of Flame. [s. 1146]