142 



PROCEEDINGS OF SECTION B. 



Sulphuric acid in rain indicates contamination of the air, 

 either by the decomposition products of organic substances, or by 

 the sea spray brought inland by winds. The combustion of coal 

 appears to be particularly a source of sulphuric acid, the air of 

 towns containing sufficient to give an acid reaction to the rain. 



Chlorine also is derived from the combustion of fuel, but the 

 greater part is obtained, at any rate at Lincoln, from sea spray. 



The extent of the impurities therefore in rain water is depen- 

 dent mainly on the population of the district and its proximity 

 to the sea, 



The following table (Table II.) will shew the analytical results 

 obtained during the past four and a half years from the rain 

 collected at Lincoln. 



Table II. — Analysis of Rain-water. 



Results expressed in parts per million. 

 1884. 



