70 Air Pollution by Coal Smoke. [april, 



The differences between the domestic and boiler soot, thus 

 obtained from the same coal, are striking and instructive. 

 The sample from the base of the boiler chimney is little more 

 than dust ; practically ail the hydro-carbons have been burnt, 

 while what few have volatilised have at the temperature there 

 prevailing no chance of recondensing. Further, the more 

 volatile constituents, ammonium-chloride and sulphate, and 

 arsenic, accumulate. The sample of domestic soot is typical 

 of all those which have been analysed by rerson of its high 

 content of tar and volatile substances and its low content of 

 ash. In some samples of domestic soot the amount of tar may 

 even reach as high as 40 per cent. 



Imparities in the Air due to Smoke. 



With a view to estimating the nature and amount of the 

 impurities in the air of an industrial town, ten representative 

 stations were selected in Leeds, and one on the University 

 Experimental Farm at Garforth, some 7! miles due east of 

 Leeds. Of the Leeds stations some were in the heart of the 

 industrial area, and others in" various residential quarters. 

 The impurities are partly in the form of suspended matter, 

 consisting of soot, tar, sand and mineral matter ; and partly 

 in solution, consisting of sulphurous and sulphuric acids or 

 their salts, chlorides, largely in the form of hydrochloric acid 

 or common salt, and nitrogenous matter. 



The figures as to the amount of solid impurities in the air 

 taken at the different stations showed that the impurities 

 diminished rapidly from the industrial area northwards into an 

 agricultural area. In the centre of the town the yearly deposit 

 was 850 lb. to the acre ; less than a mile north the figure fell 

 to 400 lb. ; and just over two miles to the north it fell to 150 lb., 

 or little more than one-sixth of the deposit in the centre of the 

 town. The investigation showed that in the chief industrial 

 centres of Leeds the solid impurities due to smoke pollution 

 are roughly twenty times as abundant as in the purer atmosphere 

 some three miles north-east, in the agricultural country. 



By far the most deleterious and objectionable of all the sus- 

 pended impurities is the tarry matter. At all stations an appre- 

 ciable amount of tar was found to be deposited, the amount 

 being greatest in and near the industrial area and diminishing 

 rapidly towards the north. 



It is interesting, however, to note that the suspended matters 

 in the suburban areas, though smaller in amount, are much 

 richer in tar than those of the industrial area. There is thus 



