234 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



At a distance of 10 miles from London, the smoky particles are small 

 and show quite a thick haze in a room with a fire, when a gentle cur- 

 rent is moving from the town. Professor Frankland has shown that 

 if a little smoky air be blown across the surface of water evaporation 

 is retarded 80 per cent. The water globules may be similarly coated 

 with tarry matter, which hinders the warmth of the sun from evaporat- 

 ing them. Moreover, every particle of carbon is a good radiator and 

 in the early morning tends to increase the cold in the air around it; 

 moisture is deposited upon it, in the opinion of the present writer, and 

 can only with difficulty evaporate, so long as radiation is active and 

 while the heat and light of the sun are stopped by smoke. The effect 

 of finely divided carbon in stopping light may be tested by holding a 

 piece of glass for a few moments above the flame of a candle; the 

 black film deposited enables us to look at the sun easily, and it appears 

 well defined, like a red orange, as in a fog. 



The imperfect combustion of coal is the cause not only of fogs being 

 specially dangerous to life, but of their persistence in duration far beyond 

 those of the surrounding country. The removal of coal smoke would 

 mean much less fog and much less evil in that which remained. Cities 

 which use wood as fuel, or anthracite, or gas, or oil, are no more visited 

 by fogs than the surrounding country, although the fine "dust" above 

 them is, according to Aitken, very greatly in excess of the normal. 



Pittsburg had a black climate till it used natural gas, and thencefor- 

 ward has had a clear air, and no special liability to darkness and fog. 

 In London, of 9,709,000 tons of coal used annually, about 1 per cent 

 escapes into the air unburn t and 10 per cent is lost in other volatile 

 compounds of carbon. The bright sunshine, compared with that of 

 Kew, 9 miles distant, was, in the four years 1883-1886, 3,925 hours, 

 against 5,713 at Kew, and about 6,880 at St. Leonards, about 80 miles 

 distant. From November, 1885, to February, 1886, inclusive, the sun- 

 shine in London was 62 hours, at Kew 222, and at Eastbourne 300. 



Town fogs contain an excess of chlorides and sulphates, and about 

 double the normal, or more, of organic matter and ammonia salts. 



During the last fortnight of February, 1891, the previously washed 

 roofs of tbe glass houses at Chelsea and Kew, the former just within, 

 and the latter just outside, London, received a deposit from the fog, 

 which was analyzed and gave the following results : 



Substances. 



Carbon 



Hydrocarbons 



Organic bases (pyridines, etc.) 



Sulphuric acid (50 3 ) 



Hydrochloric acid (HCE) 



Ammonia 



Metallic iron and magnetic oxide of iron 



Mineral matter (chiefly silica and ferric oxide) 

 Water, not determined (say difference) 



Chelsea. 



Kew. 



Per cent. 

 39 



Percent. 

 42.5 



12.3 



4.8 



2 





4.3 



4 



1.4 



.8 



1.4 



1.1 



2.G 





31.2 



41.5 



5.8 



5.3 



