ASSIMILATION OF NITROGEN. 61 



that the decay of all animal matter takes place 

 with greater rapidity during the increased 

 heats of summer, and it may be that to this 

 cause is to be attributed the grateful feeling of 

 the purity and freshness of the air which can- 

 not fail to have struck even the most insensi- 

 ble, when a long summer's drought is termi- 

 nated by a refreshing shower. 



The author before quoted,* and whose work 

 is again recommended to all who wish to mas- 

 ter the subject under consideration, here enters 

 into a variety of calculations to prove the ex- 

 tent to which ammonia exists in the atmosphere. 

 It is hardly necessary for us here to follow all 

 the details he gives, but the result may be ac- 

 ceptable. 



It is calculated that if a pound of rain water 

 contains only the fourth part of a grain of am- 

 monia, and this is a low calculation, then that 

 a field containing 40,000 square feet, would 

 receive 80lbs. of ammonia annually, presuming 

 that the fall of rain over such a surface 

 amounted to 2,500,000 pounds, the quantity 

 which on an average usually falls on such a 

 space. This is a larger quantity of nitrogen 

 than would be required by a crop of copse 

 wood, hay or turnips; but less than a field of 

 corn including the straw and roots, contain; 

 and it must here be stated, that although this 

 quantity of ammonia would be dissolved in the 

 rain that may fall, still some portion of it would 

 again enter the atmosphere with the water 



* Liebig. 



