The Atmosphere. 



33 



partly from extensive soft coal burning in a country like Eng- 

 land. It is extremely doubtful if the sulphur supply from the 

 atmosphere in the open country of the United States is as high 

 as that found at Rothamsted. It is very probably much lower 

 and not nearly sufficient for continuous crop requirements. 



Accidental constituents. In some localities the air contains 

 uncommon constituents as a result of local conditions. This is 

 true in active volcanic regions and in the vicinity of some indus- 



The effect of smelter fumes and waste on vegetation near Anaconda, 



Montana. 



trial plants. The most important of these constituents are gases. 

 Methane or marsh gas, which is a product of fermentation where 

 air is excluded and which accumulates over swamps and in mines, 

 and carbon monoxide, a product from the incomplete combustion 

 of coal, are examples of this class. Hydrochloric acid gas. which 

 escaped into the air in quantity from the old process of manu- 

 facturing soda, is an example of an objectionable, accidental con- 

 stituent of the air resulting from an industrial process. The 

 deadly effect of this gas upon vegetation led to the passage of 



