292 AGRICULTURAL ANALYSIS 



of nitrification, the whole of the nitrogen, or at least the larger 

 part of it, which has been collected in this debris, becomes 

 finally converted into nitric acid and is found combined with 

 appropriate bases as deposits of nitrates. The nitrates of the 

 guano deposits and of the deposits in caves arise in this way. 

 If these deposits be subject to moderate leaching the nitrate 

 may become infiltered into the surrounding soil, making it very 

 rich in this form of nitrogen. The bottoms and surrounding soils 

 of caves are often found highly impregnated with nitrates. 



256. Waste Nitrogen. When nitrogen has played its role in 

 vegetable and animal life it is broken' down from the organic 

 compounds it has formed by the action of organisms, or in the 

 usual processes of decay, and is oxidized again to soluble forms, 

 and may be even restored to its gaseous inorganic condition. 



257. Soils Impregnated with Nitrogen. While for our pur- 

 pose, deposits of nitrates only are to be considered which are of 

 sufficient value to bear transportation, or to warrant their con- 

 centration by leaching, yet much interest attaches to the formation 

 ot nitrates in the soil even when they are not of commercial im- 

 portance. 



In many of the soils of tropical regions not subject to heavy 

 rain-falls, the accumulation of these nitrates is very great. 

 Muntz and Marcano have investigated many of these soils to 

 which attention was called first by Humboldt and Boussingault. 52 

 They state that these soils are incomparably more rich in nitrates 

 than the most fertile soils of Europe. The samples which they 

 examined were collected from different parts of Venezuela and 

 from valleys of the Orinoco, as well as on the shore of the Car- 

 ibbean Sea. The nitrated soils are very abundant in this region 

 of South America where they cover large surfaces. Their compo- 

 sition is variable, but in all of them carbonate and phosphate of 

 lime are met with and organic nitrogenous material. The nitric 

 acid is found always combined with lime. In some of the soils 

 as high as 30 per cent, of nitrate of lime have been found. Nitri- 

 fication of organic material takes place very rapidly the year 

 round in this tropical region. These nitrated soils are everywhere 

 " Comptes rendus, 1885, 101 : 65. 



