THE AIR OF TOWNS. 



373 



February 14, 1882. Very fine 0.041 



December 8, 1882. Fine 040 



December 10, 1882. Thick, white fog 094 



December 11, 1882. Tbick, white, darker 110 



December 11, 1882. Later very dark 141 



March 31, 1883. Fine 037 



April 3, 1883. Very foggy 133 



You will notice that where the fog is long continued the amount of 

 this gas increases threefold. 



The next slide gives the average amount of sulphurous acid in Man- 

 chester air during four months of 1892, as determined by the Manchester 

 Air Analysis Committee: 



Sulphurous acid in Manchester air. 

 [Milligrams of S0 3 per 100 cubic feet.] 



Month. 



Minimum. 



Maximum. 



Average. 





0.7 

 6.7 

 2.0 

 3.0 



3.5 



6.0 

 12.0 

 30.0 



1- 2 



2- 4 

 6- 8 

 6-10 











And the following table gives a number of determinations from 

 the same source in the outskirts and the center of the town, showing 

 plainly the increase of acid during fog and the larger proportion in the 

 center of the town : 



[Milligrams of S0 3 in 100 cubic feet.] 



Date. 



Outskirts. 



Center of 

 town. 





0.7 

 0.8 

 1.7 



2.5 

 3.3 

 2.0 

 2.96 

 4.2 

 9.3 

 2.3 

 16.5 

 12.7 

 12.7 



1.8 



3.53 



4.9 



4.1 



7.6 



5.9 



8.4 



«9.7 



a 15. 7 



9.2 



a 32. 2 



a 22. 6 



a 25. 8 





November 5 







November 19 





December 17 . . . 









a Fog. 



I should now like to explain to you briefly the apparatus which I 

 devised for the Manchester Air Analysis Committee for making these 

 determinations of sulphurous acid. 



The apparatus used for the determination of sulphurous acid in the 

 air consists of three parts (fig. 29). A, a long glass tube, about half 

 an inch in diameter, open at both ends, which is fixed horizontally so 



