AGRICULTURAL TEXT-BOOK. 1 1 



Liebig (Agri. Chem.) observes &quot; that tlio ammonia contain 

 ed in rain and snow water possesses an offensive smell of per 

 spiration and animal excrements, a fact which leaves no doubt 

 respecting its origin.&quot; These experiments have been repeated 

 in France, Germany, America, and England with the same re- 

 suite. It is probable that in the neighborhood of large cities, 

 and in densely peopled countries, the air contains a much larger 

 proportion of this valuable alkali, than in the wild and thinly 

 settled districts. Some curious agricultural and pathological 

 phenomena may be explained by these facts ; but the subject 

 still requires more extended and minute examination. 



32. Henry and Chevallier have detected acetic acid and 

 probably hippuric acid in the atmosphere. Horsford supposes, 

 as the result of his experiments, that the organic effluvia in the 

 air are of acid character. 



33. Ozone, also, appears to vary in quantity. 



Ozone is believed to be a form of oxygen, and is produced when elea- 

 tric sparks are taken through perfectly dry oxygen. It is formed in tha 

 air during thunder storms. Air impregnated with it acts very much a* 

 if a trace of chloiine gas were present, which ozone appears to resemble. 

 Little is yet known of it, but it probably has some connection with 

 LealtL and epidemic illness ; and is suspected to act on plants by effect 

 ing their growth. 



34. Yaughan (Am. Assoc. of Science,) states that by means 

 of feeble currents of electricity, the amount of carbonic acid 

 which water and moist surfaces continually absorb from the air, 

 is decomposed, and serves to supply the principal part of tbi 

 humus of the soil. 



35. Although, they have not been detected, there can be Tto 

 doubt that the Sporules (seeds) of minute Cryptogamic plant% 

 such as Mould, Rust, d-c., are generally floating in the air, 

 ready to take root wherever they find proper conditions. The 

 atmosphere is also full of Animalcules and infusorial forms. 



36. Dr. Smith (Proc. of British Assoc.) in experiments on 



