354 THE AIR OF TOWNS. 



accumulation of carbonic acid wherever vegetation is allowed to flour- 

 ish, and where the quantity of carbonic acid does not accumulate too 

 rapidly to be dealt with by nature in this manner. 



It is therefore obvious that overcrowding, want of open spaces, and 

 the absence of vegetation favor the accumulation of carbonic acid. 



Overcrowding has, however, been dealt with by legislation, and 

 where legislation steps in we may be sure that the evil is a real and 

 a pressing one. 



Governments and municipalities have recognized the importance of 

 open spaces, of streets of a certain width, of open spaces at the backs 

 of houses, of a certain number of cubic feet for each inmate in lodging 

 houses, hosxfltals, workhouses, prisons, etc. 



This will help to check the accumulation of carbonic acid. But 

 although people are content to live in crowded and smoke-laden towns, 

 vegetation is not so easily persuaded to forego its natural atmosphere, 

 and the smoke question must be dealt with before we can stop the 

 deposition of soot and let in the sunlight to give the necessary vitality 

 to plant life, which should flourish in the very center of our big towns. 

 Let us see now what the evil is. Here is a table showing carbonic 

 acid found in different places : 



Carbonic acid in the air. 1 



Volume, per cent. 



In mines, largest amount found in Cornwall 2. 5000 



Average of 339 analyses - _ 0. 7850 



In theaters, worst parts as much as 0. 3200 



In workshops, down to 0. 3000 



About middens 0. 0774 



During fogs in Manchester 0. 0679 



Manchester streets, ordinary weather 0. 0403 



Where fields begin , 0.0369 



On the Thames at London 0. 0343 



In the London parks and open places 0. 0301 



In the streets 0.0380 



On the hills in Scotland, from 1,000 to 4,406 feet high 0. 0332 



At the bottom of tho same hills 0. 0341 



Hills below 1,000 feet 0.0337 



Hills between 1,000 and 2,000 feet 0.0334 



Hills between 2,000 and 3,000 feet 0.0332 



Hills above 3,000 feet 0.0336 



The amount seems very small. Perhaps the following diagram will 

 represent the proportion more graphically: 



The diagram (fig. 9) is divided into squares showing the proportion 

 of nitrogen, oxygen, and carbonic acid in the volume of air indicated 

 by the large square. 



Although the proportion of carbonic acid in good and bad air is so 

 inconsiderable, we must not be led into supposing that the difference is 

 negligible. There are many examples known to the chemist in which 



' Annus Smith. 



