THE AIR OF TOWNS. 



363 



green color then bleached, without disturbing the sooty deposit on the 

 other half. 



The diminished amount of sunlight received iu the town of Leeds 

 may be gathered from the simultaneous records taken at the Philo- 

 sophical Hall and at Adel (4 miles from the city). In the year 1892, there 

 was 43 per cent, and in 1893, 30 per cent more sunshine at Adel than 

 in Leeds. This is the record of hours of sunshine, but not of its inten- 

 sity. The latter, had it been recorded, would probably have shown a 

 still greater difference. 1 I said that the snow in the parish churchyard 

 contained acid — sulphuric acid. This acid is, like soot, derived from 

 coal, for it is never found in the country. The sulphur in the coal, 

 which is present to the extent of from 1 to 3 percent, burns, and a por- 

 tion passes up the chimney as sulphurous acid, and then into the open 

 air. It is this sulphurous acid which imparts to town fog its choky 

 and irritating effects. In the open air it is rapidly converted into the 

 much more corrosive substance — sulphuric acid, which nearly always 

 accompanies soot, and it is found with soot on leaves, and probably 

 promotes their early withering near towns. Moreover, it corrodes the 

 mortar and stone work of our buildings. 



The following table, prepared by the Manchester air analysis com- 

 mittee, gives the analyses of deposits upon leaves gathered in and near 

 the city. The places are arranged in the order as we pass from the 

 outskirts to the center of the town : 



Deposits on holly or aucuba leaves collected December 14-16, 1891. 

 [Milligrams per square meter ol leaf surface.] 



Locality. 



Alexandra Park 

 Owens College.. 



Hulme 



Harpurhey 



Infirmary 



Albert Square . . 



Solid Sulphuric 

 matter. acii. 



131 

 315 

 420 

 443 

 728 

 833 



7.2 

 10.4 

 26.0 

 19.0 

 27.5 

 24.2 



•It has been said that however much you may do away with smoke, 

 you will never remove this acid; it will still pass into the air. Quite 

 true; but to anyone who advances that as an excuse for the smoke 

 maker, I would say this : Soot is an oily substance not wetted by water. 

 The acid, therefore, attached to it is not washed away by rain so rapidly 

 as it certainly would be, if it were not in contact with this film of oily 

 matter. Although sulphurous and sulphuric acids are injurious to 

 plants, I do not believe the quantity given off from our chimneys would 

 prove nearly so hurtful as it is now in company with soot. 



There are real or imaginary difficulties in the way of stopping smoke 

 from house fires, yet I firmly believe that before another generation has 



■Since this lecture was delivered experiments on the intensity of the light have 

 been made and will be found in Appendix II. 



