292 



NATURE 



[December 29, 1910 



to be found sulphur compounds, such as sulphuretted 

 hydrogen and sulphur dioxide, the first formed during the 

 distilling period when coal has just been fed on to the 

 fire, and the latter during the combustion. Both these 

 compounds are due to the sulphur always present in the 

 coal, and whilst the former blackens white-lead paint and 

 tarnishes silver, the sulphur dioxide, dissolving in water, 

 oxidises to sulphuric acid, which is far more actively 

 injurious, corroding and destroying metal work, retarding 

 the growth of vegetation, and finally killing it. 



Smoke thus formed finds its way from the chimney 

 into the atmosphere, and is rapidly diffused through the 

 air by means of the air currents, and it is manifest that 

 if there were no means of removing it the air would 

 soon become perfectly opaque from its accumulation in 

 large quantities. When, however, rain falls, it rapidly 

 washes the air free from such suspended solid and liquid 

 impurities which constitute the visible portion of smoke. 

 Snow is even more efficacious than rain in doing this ; 

 where the snow has fallen on the glass roof of a green- 

 house it will be noticed that when it melts it leaves 

 behind a black deposit consisting of the solid matter 

 which it has collected during its passage through the air. 

 An analysis of a deposit of this character formed on the 

 glass roofs of some orchid houses at Chelsea gives a verv 

 good idea of the constituents of these solid impurities : — 



Per cent. 



Carbon ... ... ... ... ... ... 39-00 



Hydrocarbons ... ... ... ... ... 12-30 



Organic bases ... ... ... ... ... 1.20 



Sulphuric acid ... ... ... ... ... 4.33 



Ammonia ... ... ... ... ... 1.37 



Metallic iron and magnetic oxide ... ... 2-63 



Other mineral matter, chiefly silica and 



ferric oxide ... ... ... ... ... 31-24 



Water not determined. 



In cases where long drought prevents the rapid clear- 

 ance of the air by this means, the heavier of the solid 

 particles settle by gravity, whilst the particles of carbon 

 and carbonaceo;js organic matter are slowly oxidised by 

 the oxygen and ozone into carbon dioxide, in which form 

 vegetation removes them from the air. 



The solid particles suspended in air are, however, by 

 no means confined to the products of our improper use 

 of bituminous fuel, and mineral matter from the dust of 

 our roadways and organic matter from animal and vege- 

 table life all play their part in rendering town air 

 deleterious to health ; but it is the smoke " dirt " that 

 is the most injurious factor. 



The smoke from our grates is naturally discharged at 

 a lower level than that from the factory shafts, with the 

 result that it probably has a greater effect on our general 

 health and buildings than the higher layers of smoke, 

 which travel for miles with the wind and which act more 

 by darkening the sky and cutting off the sun's rays; and 

 it is also clear that the low-level smoke will not extend 

 so far from the point .at which it is formed,, as contact 

 with buildings and vegetation rapidly rob it of the tar 

 vapours, with the result that in a smoky town like Leeds 

 it has been shown that at one mile out the solid impuri- 

 ties have fallen to one half, and at 7.\ miles out to one- 

 sixth. 



Injurious as are the direct effects of smoke on health 

 and property, they are small as compared with those 

 brought about by dense fog, which may to a great extent 

 be attributed to smoke, which acts partly by helping its 

 formation and partly by retarding its dispersion. 



Fog, whether it be in the form of white mist which 

 is found in the country, or the yellow abomination which 

 we know so well in London, is formed by the condensation 

 of water vapour from the air, and this is brought about 

 by anv cause which rapidly cools a large volume of moist 

 air. If, instead of the surface of the ground and the 

 objects on it only being cooled the air for a considerable 

 height above it is also lowered in temperature, then the 

 moisture which is deposited from it, instead of forming 

 dew, condenses in the air, forming minute vesicles that 

 remain suspended and floating in the air, and con- 

 stitute fog or mist. In pure air the mist so formed 

 consists of little else than these minute bubbles of water, 

 and has no irritating effect on the eyes or lungs. In a 



NO. 2148, VOL. 85] 



large town like London, however, the air is charged with 

 an enormous number of minute particles, the heaviest of 

 which settle on a horizontal or roughened surface in the 

 form of dust, whilst the lighter particles continue floating 

 in the air. These particles consist of a heterogeneous 

 collection of all kinds of matter, amongst which " smoke " 

 particles bulk largely, constituting more than one half. 

 -All these floating solids cool with great rapidity on account 

 of the smallness of their size, and in doing so cause the 

 rapidly cooling air to deposit moisture upon them, and 

 so aid in the formation of the town fog, which appears 

 long before the country mist. 



The air of towns in which much coal is used also 

 contains the volatile tarry matter distilled off during the 

 imperfect combustion, and this, condensing with the 

 moisture, coats it on the outside with a thin film, which 

 does much to prolong the existence of the fog, as when 

 the temperature of the air again rises the clean mist 

 again evaporates into the atmosphere, but the tar-coated 

 yellow fog has its power of evaporation retarded to an 

 enormous extent. Experiments made by Sir E. Frank- 

 land show that the evaporation of water in dry air isj 

 reduced nearh" 80 per cent, by blowing some smoke from ' 

 burning coal on to its surface. 



The statements made as to the enormous waste of fuel i 

 in the escaping smoke are, I think, often much ex- ' 

 aggerated. In point of fact, the carbon wasted as soot 

 is extremely small, and varies in smoke with the stale 

 of the fuel which is fed on to the fire. Under the ordinary 

 conditions experienced in an open fire grate, in which the 

 fire has just been made up with bituminous coal, the 

 hea%-y smoke escaping will contain, on an average, \\ per 

 cent, of the total weight of fuel consumed, and as the 

 temperature of the mass gradually increases this falls to 

 less than \ per cent. 



A greater waste of the thermal value of the fuel takes 

 place in the formation of the smoke, i.e. in the heat 

 rendered latent in bringing about the decomposition of 

 the coal, and the volatilisation and escape unburnt of the 

 tar vapours formed. 



Having gained an idea of the causes which give rise 

 to smoke from the domestic hearth, we can now review 

 the proposals which have from time to time been made 

 for its prevention, and which may be classified under the 

 headings : — 



(i) The use of bituminous fuel in special grates. 



(2) The use of solid smokeless fuel. 



(3) The use of gaseous fuel. 



(4) The combined use of gas and coke. 



(5) Central heating by steam, water, or hot air. 



In considering the claims of these various methods we 

 must remember that the English open fire is undoubtedly 

 the most comfortable and wasteful method of heating that 

 could be adopted ; but although by far the largest propor- 

 tion of the heat escapes up the chimney, we must clearly 

 bear in mind that this very factor makes it a most 

 important engine of ventilation, and that at this time, 

 when the ventilation of our middle-class houses is chiefly 

 left to the jerry builder and the open fireplace, it is an 

 important factor of health. Moreover, it heats the room 

 in the only healthy way, that is, the radiant heat from 

 it does not directly raise the temperature of the air, but 

 is radiated to the floor, walls, and furniture in the room, 

 which again part with their heat slowly to the air in 

 contact with them and to the inhabitants, so that the 

 walls and other solid matters in the room are at a higher 

 temperature than the air. 



Apart from its being more healthy to breathe cool than 

 hot air, there is another important point to consider, j 

 The normal temperature of the body is q8° F., or 36-8° C., 

 and this temperature is maintained by the slow combustion : 

 processes going on in the body. By the laws of radiation | 

 a heated surface parts with its heat more or less rapidly 1 

 according to the temperature of the surrounding bodies, 

 so that if a person be sitting in a room filled with warm | 

 air, but near a wall colder than the air, his body will ; 

 rapidlv part with heat by radiation to the wall, and a ^ 

 sensation of chill is the result ; but with the open fire j 

 this is never the case, as the radiant heat from the fire 

 heats the walls of the room to a temperature higher than : 

 that of the air. But when a room is heated bv means of 

 hot-water pipes or warmed air, the walls not being heat^^ 



