THE NITIM 



oi'^ TU.: sui:.. '257 



either that absorbed by the sol from the atmospliere, or 

 tliat originating in the soil itself by the decay of nitrog- 

 enous organic matters. Knoj) made an experiment with 

 a sandy loam, as follows : The earth was exposed in a box 

 to the vapor of ammonia for three days, was then mixed 

 thoroughly, spread out thinly, moistened with pure water, 

 and kept sheltered from rnin until it became dry again. 

 At the beginning of the experiment, 1,000,000 parts of 

 the earth contained 52 parts of nitric acid. During its 

 exposure to the air, Avhile moist, the content of nitric acid 

 in this earth increased to 591 parts in 1,000,000, or more 

 than eleven times ; and, as Knop asserts, this increase took 

 place at the expense of the ammonia which the earth had 

 absorbed. The conversion of ammonia into nitric acid is 

 an oxidation expi*essed by the statement 



2 NH3 + 40 = NH, NO3 + 11,0. * 

 The oxygen may be either ozone, as already explained, 

 or it may be furnished by a substance which exists in all 

 soils and often to a considerable extent, viz., sesquioxide 

 of iron. This compound (Fe,^ O3) readily yields a portion 

 of its oxygen to bodies which are inclined to oxidize, be- 

 ing itself reduced thereby to pi-otoxide (FeO) thus : — 

 Fe, O3 = 2 FeO + O. The protoxide in contact with the 

 air quickly absorbs common oxygen, passing into sesqui- 

 oxide again, and in this way iron operates as a carrier of 

 atmospheric oxygen to bodies whicli cannot directly com- 

 bine with the latter. The oxidizing action of sesquioxide 

 of iron is proved to take place in many instances ; for ex- 

 ample, a rope tied around a rusty iron bolt becomes " rot- 

 ten," cotton and linen f ibrics are destroyed by iron-stains, 

 the head of an iron nail corrodes away the wood sur- 

 rounding it, when exposed to the weather, and after suf- 



* The above equation represents l)iit one-half of the ammonia as converted 

 into nitric acid. In the soil the carbonates of lime, etc., would separate the 

 nitric acid from the remaining ammonia and leave the latter in u condition to 

 be oxidized. 



