362 THE AIR OF TOWNS. 



direction, that the waste of fuel in the form of im burnt coal passing 

 into the air is prodigious. Estimated for the whole country, it would 

 mean not an insignificant item of loss to the nation. 



Before we can understand the effects of smoke we must learn its 

 composition. I have analyzed two samples, one of which was deposited 

 on the orchid houses at Chelsea during fog, and the other was obtained 

 from my chimney sweep. They contained respectively 14 and 15 per 

 cent of a nasty, sticky oil. Were the soot pure carbon it would be 

 comparatively harmless. It would possess no smell, it would not adhere 

 to anything, and the first fall of rain would wash it away. Unfortu- 

 nately, this is not the case. Wherever the soot alights a great part of 

 it sticks, and no amount of rain water will remove it. That is why our 

 buildings become permanently black and foliage is discolored. 



In order to demonstrate to you the effects of this sticky material 

 in the soot, I analyzed the deposit on three glass plates, 1 foot square, 

 which have been stationed in different spots — one at Pool (about 9 

 miles from the center of Leeds), one on the roof of the Yorkshire 

 College (about 1 mile from Leeds), and one on the roof of the Philo- 

 sophical Hall (in the town) — all being removed from the immediate 

 neighborhood of chimneys. This is the appearance (fig. 17) which 

 two plates present after a years' exposure, one in the country and the 

 other in town. A remained clean and transparent, whereas B was 

 quite opaque. 



A series of experiments of this nature extending over many months, 

 in which the deposit after washing was weighed, showed that the 

 deposit on the Philosophical Hall plate was twenty-four times and on 

 the Yorkshire College plate ten times that on the Pool plate, the latter 

 being insignificant in quantity. 



The effect of breathing such a filthy atmosphere can only be indi- 

 rectly gauged. That it plays no insignificant part, by clogging the air 

 passages, in bringing about the high mortality from respiratory diseases, 

 so conspicuous in all industrial towns, can not for a moment be doubted. 

 Its fatal effects upon vegetation are obvious. The green leaf of the 

 plant is its perspiring organ, and the leaf is provided with little pores — 

 the stomata. When these get clogged with soot the plant dies, just as 

 a human being would if the pores of his skin were closed by a layer of 

 varnish. But the soot in the air does more than this. The plant 

 derives the principal material for its growth from the carbonic acid in 

 the air. By the aid of the green coloring matter, the chlorophyll, which 

 is found in the leaf or stem, the carbonic acid of the air is decomposed, 

 the oxygen being restored to the atmosphere and the carbon retained 

 by the plant. This process only occurs vigorously in sunlight. What, 

 then, must be the effect of the black deposit upon the leaf in shutting 

 out that light, and what must be the effect of the smoke-laden air in 

 X>reventing the passage of the sun's rays? 



Here are i>hotographs of two leaves gathered near the town (fig. 

 18). From half of each the deposit of soot has been wiped off and the 



