142 THE MEW AU1UCULTUKE. 



most perfect purifier of water containing organic impurities; this 

 is demonstrated by natural facts. Spring water, generally so pure 

 and limpid, proceeds from surface waters polluted with vegetable 

 and animal impurities, but becomes purified during its passage 

 through the earth. This evidence furnished by springs, is confirm- 

 ed by practical results of the irrigation of sewerage instituted in 

 England and France. Finally, the proof is made conclusive by 

 analysis and scientific experiments that perfect artificial filtration 

 can produce water almost as pure as spring water. 



""Water, more or less polluted, having passed through a deep 

 filter composed of sand, containing a small percentage of argillous 

 matter, the insoluble particles are stopped at the surface and the 

 more minute particles are retained deeper in the body of the filter. 

 This is the first result produced, it is a simple mechanical filtra- 

 tion. The water being cleansed of the insoluble matter, descends 

 deeper; each particle of sand is drenched with a thin film of water; 

 thus divided, the water offers to the confined air in the earth or 

 filter an enormous surface of action. Now commences the second 

 effect of perfect filtration and aeration, which is the combustion of 

 the organic matter in solution in the water. It is a general saying 

 that fire purifies everything, and indeed there is no organic matter, 

 so impure or so unhealthy, which fire, with the aid of the oxygen 

 of the air, will not transform into carbonic acid, water and nitro- 

 gen. In the interior of this filter a purification likewise takes 

 place, not violent and visible like that caused by fire, but slow and 

 without any perceptible evidence; nevertheless it is a combustion 

 which reduces all organic impurities to carbonic acid, water and 

 nitrogen. It is even a more perfect combustion than that caused 

 by fire, producing oxydation of the nitrogen and the formation of 

 nitric acid, a result which fire cannot produce. 



" In conclusion, I will say that the filtration and aeration of all 



