40 BOARD OF AGRICULTURE. 



tations from people living along the right bank of the river 

 followed very closely the opening of the two great sewers ; 

 and the state government required the city of Paris to seri- 

 ously consider methods of purifying the sewage before dis- 

 charging it into the river. The savants, engineers, chemists, 

 traders and agriculturists discussed the subject in all its 

 phases, and to the latter we are indebted for a practical 

 solution of the problem. 



Filtcragc was naturally the first system to be tried. It 

 was soon found that, besides the actual difficulties of filtra- 

 tion on so large a scale, this mode of treatment had the 

 capital vice of leaving in the water soluble organic matter 

 capable of fermentation, and later, chemical agents were 

 resorted to with the object of precipitating the soluble matter, 

 but only incomplete results were obtained, which were slow, 

 costly, and inapplicable on so large a scale. 



We now come to the experiment which after fifteen years 

 of study and persevering eflfort has given a result most 

 complete and satisfactory. Epuration and utilization by 

 agriculture, and filtration by spreading the sewage on per- 

 meable land, have accomplished this end. It is based on 

 simple principles, of which the demonstration is now made. 

 All argilo-silicious and permeable soils, sufiiciently thick and 

 well-drained, have the property of retaining in their superior 

 layers all the organic matter in suspension and solution con- 

 tained in drain water spread on the surface of the land. 

 Such soil can receive without being made damp or marshy 

 one inch of water per day, or twenty-six feet per year. It 

 transforms the retained organic matter, rendering it capable 

 of assimilation by plants. 



A very large proportion of the water used in irrigation is 

 evaporated either directly or by the plants in vegetation. 

 The residuary water coming from the subsoil drains is of a 

 remarkable purity, and does not suggest, either by aspect or 

 composition, the sewage from which it proceeds. 



Trusting in these princi[)les, and fortified by the works of 

 Messrs. De Freycinet, Schloessing, Mario-Davy and Frank- 

 land, the engineers of the municipal service, have, since 18G7, 

 pursued studies and made experiments for which, notably 



