30 



ACCIDENTAL IMPURITIES 



parts of sulphuric acid per million were found. It was noticed that 

 the rime deposited on the leaves of plants during frost sometimes con- 

 tained as much as 400 parts of sulphuric acid per million. 



Organic matter of a readily putrescible nature is also present in 

 air where respiration of men or animals or decay of organic matter 

 (e.g. in marshy and malarious districts) takes place. To this organic 

 matter, perhaps, rather than to the increased carbon dioxide and 

 diminished oxygen, the bad effects of breathing the atmosphere of 

 close and crowded rooms are to be ascribed. This organic matter is 

 probably suspended, but is very finely divided. 



In 1906 to 1910, Growther and Kuston 1 examined the rain falling 

 in and near the city of Leeds, with especial reference to the total sus- 

 pended matter, acidity, sulphur as sulphur trioxide and in other forms 

 (chiefly H 2 S and S0 2 ), chlorine and nitrogen (as ammonia, nitrates 

 and in organic combination.) They also divided the suspended matter 

 into ash, tarry matter soluble in ether, and soot. 



Samples were collected from eleven stations, three, Nos. 1, 2 and 4, 

 being in industrial parts ; two, 6 and 7, in city residential parts ; five, 3, 

 5, 8, 9 and 10, in suburban residential districts and one, 11, at Gar- 

 forth, 7 miles to the east of the city. 



Their results are briefly summarised in the following table in Ib. 

 per acre, per annum : 



The high figures for chlorine found <in stations 1 and 2 are 

 accounted for by the salt glazing carried on at fireclay works in the 

 neighbourhood. 



Direct determinations of the average intensity of daylight (as 

 measured by the amount of iodine set free from a dilute acid solution 

 of potassium iodide) showed that the smoke pall over station 2 in the 



1 Jour. Agric. Sci., 1911, 4, 25. 



