AGRICULTURAL TEXT-BOOK. 



Its proportion near the surface of the earth, is greater in sum 

 mer than in winter, and during night than during day. It is 

 dLso more abundant on the summits of high mountains than in 

 the plains, 



27. COMPOSITION OP DRY AIR BY VOLUME. 

 Kitrogen, - ?912 

 Oxygen, - - 2080 

 Carbonic acid, 4 

 Carburetted hydrogen, 4 

 Ammonia, (3 vols. of hydrogen with one of 



nitrogen,) - - - varies 



Ozone, - &quot; 



Organic matter, and salts, - 



28. Prof. Hereford, in experiments made in Boston, Mass., in 

 1849, (Am. Assoc. of Science,) found the quantity of ammonia 

 in. the air greatly to exceed that detected by Freseuius, at Wies 

 baden. Liebig, at Giessen, found it in rain-water and snow ; and 

 estimates that one pound of rain-water contains a quarter of -a 

 grain of ammonia. * 



&quot; 4 field of 26,910 square feet must receive annually upwards of 88 Ibs. 

 of ammonia ; or 71 Ibs. of nitrogen ; for by the observations of Schub- 

 ler, about 770,000 Ibs. of rain falls over this surface in four months, and 

 consequently the annual fall must be 2,310,000 Ibs.&quot; Liebig, Agricul. 

 Chemistry, 



Liebig assumes, and justly, that such salts as are found in rain 

 water must have been held in suspension in the air, and washed 

 out by the shower. 



29. M. Barrall, of Paris, has lately examined the composition 



The following table exhibits the results of several determinations by Prof. Here 

 ford, at Boston, Mass., of the relative quantities of ammonia found in rain and snow 

 \rater. 



AMM051A IK RiEt AITO WELTED 8!fOW IK OKE CCBIC METRE. 



1S1D Dec r 22, in rain, 1.56 grains. 



&quot; 29, in snow, 2.63 &quot; 

 1350 April 4, in rain, 0.24 &quot; 



1850 March 18, in snow, 1.49 grains. 



&quot; 22-3, in snow, 0.96 

 July 16, in rain, 1.29 * 



4, in snow, 0.72 



Annual of Scientific Discov. 1851, p. 



