THE NITRIC ACm OP THE SOIL. 263 



free nitrogen is based upon the effects of a reducible 

 body, like sesquioxide of iron or sulphate of lime, to 

 •which attention has been already directed. 



In a very carefully conducted experiment, Cloez * trans- 

 mitted atmospheric air purified from suspended dust, and 

 from nitric acid and ammonia, through a series of 10 large 

 glass vessels filled Avith various porous materials. Vessel 

 No. 1 contained fragments of unglazed porcelain ; No. 2, 

 calcined pumice-stone ; No. 3, bits of well-Avashcd brick. 

 Each of these three vessels also contained 10 grms. of car- 

 bonate of potash dissolved in water. The next three vessels, 

 Nos. 4, 5, and G, included the above-named porous materials 

 in the same order ; but instead of carbonate of potash, they 

 were impregnated with carbonate of lime by soaking in 

 water, holding this compound in suspension. The vessel 

 No. 7 was occupied with Meudon chalk, washed and 

 dried. No. 8 contained a clayey soil thoroughly washed 

 with water and ignited so as to carbonize the organic 

 matters without baking the clay. No. 9 held the same 

 earth washed and dried, but not calcined. Lastly, in No. 

 10, was placed moist pumice-stone mixed with pure car- 

 bonate of lime and 10 grms. of urea, the nitrogenous princi- 

 ple of urine. Through these vessels a slow stream of puri- 

 fied air, amounting to 160,000 liters, was jjassed, night and 

 day, for 8 months. At the conclusion of the experiment, 

 vessel No. 1 contained a minute quantity of nitric acid, 

 which, undoubtedly, came from the atmosphere, having 

 escaped the purifying apparatus. The contents of Nos. 

 2, 4, and 5, were free from nitrates. Nos. 3 and 6, con- 

 taining fragments of washed brick, gave notable evidences 

 of nitric acid. Traces Avere also found in the Avashed 

 chalk. No. 7, and in the calcined soil. No. 8. In No. 9, 

 filled Avith washed soil, niter was abundant. No. 10, 



* Rcoheiclies sur la Nitrification— Legons de Chimie professtee en 1861 4 I4 

 Soci6t6 Chimique de Paris, pp. 145-150. 



