MANURING IN THEORY AND PRACTICE. 



113 



It thus appears that in Paris the quantity of 

 nitrogen hrought down in rain is six times as great 

 as it is in the open country of Alsace, a result no 

 douht due to the ammonia evolved during the com- 

 bustion of fuel and to animal exhalations. To the 

 same cause the large qiiantity contained in the mois- 

 ture of the fogs of Paris may also be attributed. We 

 also observe that dew is much richer in plant-food 

 than rain, which may serve to some extent to explain 

 its remarkably invigorating effect on vegetation. 



Again, in the valuable publication previously re- 

 ferred to, are given the following analyses of rain, 

 dew, and hoar-frost, made by Dr. Prankland from 

 samples collected at Eothamsted, Hertfordshire : — 



Table showing the Maximum, IUEinimum, and 

 Mean AijouNTs op cektain Constituents in 

 Sixty-nine Samples op Eain-wateb in Paets 

 PER Million. 



Highest proportion 

 Lowest proportion 

 Kean, 69 samples 



at 



3 



o 



85-8 



6-2 



33-1 



16-5 

 0-0 

 3-1 



16-0 

 0-0 

 47 



Turning to the analyses of dew and hoar-frost, the 

 samples examined embraced many distinct deposits : — 



Table SHomiNG the Maximum, Minimum, and 

 Mean Amounts of cektain Constituents in 

 Seven Samples op Dew and Hoar-fbost nf 

 Parts per Million. 



3-5 ISO 

 5-3 190 



I 



These small deposits condensed from the lower 

 stratum of the atmosphere contain on an average 

 three or four times the' amount of organic carbon, 

 organic nitrogen, ammonia, and nitric acid, found in 

 heavier falls of rain-water. 



The total quantity of solid matter and the amount 

 of chlorine and sulphuric acid is also larger. 



* By "hardness" is understood the total lime and mae- 

 nesia in a water, expressed In parts of carbonate of cal- 

 cinm. + The mean of thirty-four analyses only. 



X The mean of four analyses only. 



56 



Arranging the analyses of the Rothamsted rain- 

 waters, according to the quantity of the rainfall 

 and according to the various seasons of the year, we 

 obtain the following valuable results : — 



Table showing the Average Amount of Nitrogen 

 AS AlMmonia in Monthly Rainfalls op diffe- 

 rent Quantity, in Summer, Winteb, and the 

 "Whole Year. 



The gradual decrease in the proportion of ammo- 

 nia per million of rain, as the rainfall of the month 

 becomes greater, is plainly shown by these figures ; 

 the quantity of ammonia brought down per acre, 

 nevertheless, rises with each increase in the quantity 

 of rainfall; but, taking the figures for the whole 

 year, it requires the rainfall to be increased about 

 six-fold in order to double the quantity of ammonia 

 contributed to an acre of land. 



Determinations of chlorine in monthly mixtures of 

 rain-water have been carried out in the Rothamsted 

 Laboratory since June, 1877. In the next table the 

 determinations in seventy-two monthly rainfalls are 

 grouped according to the amount of the rainfall and 

 to the season of the year : — 



Table showing the Average Amount or Chlorine 

 IN Monthly Rainfalls of diiferest Quantity, 

 m Summer, "Winter, and the "Whole Year. 



