MANUEE. 207 



OKAMMES. GBAINS. 



Ammonia, 3.61 = 55.'7 



Chlorine, 2.27 = 35. 



Lime, 9-48 = 100. 



Magnesia, '. 2.12 = 32.'7 . 



" He did not ascertain whether all these substances 

 are contained in rain water collected at a distance 

 from towns. But Dr. Bence Jones found at least 

 nitric acid in rain water collected in London, at 

 Kingston in Surrey, at Melbury in Dorsetshire, and 

 far from any town at Clonakelty, in Ireland. If we 

 assume that M. Barral's averages represent what 

 occurs on an English acre, the quantity of such sub- 

 stances deposited on that extent of ground may be 

 safely estimated as follows: 



" The average depth of rain which falls in the neigh- 

 borhood of London is well ascertained to be about 

 twenty-four inches per annum. This is at the rate of 

 87,120 cubic feet, or 2,466 cubic metres of rain water 

 per acre ; and this, according to the proportions per 

 cubic metre in' the preceding table, would afford anu- 

 ally of — 



Nitrogen, 45^ lbs. 



Nitric acid, 103 " 



Ammonia, 19j " 



Chlorine, ...... 12 J " 



Lime, ..:.... 86 " 



Ulagnesia. . . * . . . 11 " 



Amount total per acre. 227 " 



