1870.] of Sewage Irrigation. 19 



dispensed with. By the process of irrigation, too, fertilizing matter 

 is distributed over the land with uniformity, and it is presented to 

 the plant in such a state that it is at once ready to be assimilated, 

 that is, it is at once food for the plant ; the plant grows more ra- 

 pidly, the period of growth is greatly shortened, and, consequently, 

 we get a greater number of crops in a given period, under the 

 irrigation system, than could possibly be obtained under any pro- 

 cess of dry manuring. The quantity of water mixed with the solid 

 matters in the ordinary sewage of towns is very great, and it has 

 been estimated that, including rainfall, 350 parts of water are em- 

 ployed in removing one part of excrement; thus the sewage is 

 delivered to the land in a very diluted state, but, as has been 

 proved by results, by no means too weak for useful application. 

 The strength of pure sewage would be far too much for vegetation, 

 and, instead of improving it, would tend utterly to destroy it ; but 

 thus diluted it is reduced to a state in which it appears to be most 

 readily absorbed by the earth, and thence taken up by plants as it 

 is required for their nourishment. 



In order to meet the requirements of local circumstances, where 

 land is not available for purposes of irrigation, attempts have from 

 time to time been made to separate the solid particles from the 

 fluid, the former being made into a species of artificial manure, 

 whilst the latter is allowed to pass away into the most convenient 

 channel for its escape. The value of the manurial ingredients held 

 in solution, being to that contained in the solid portions as six to 

 one, the great fertilizer ammonia also being afloat in the liquid 

 portion, it is not to be wondered at that these experiments have 

 invariably failed, and the works erected for carrying out the 

 different processes have, almost without exception, been abandoned. 

 After filtration, the general plan has been to mix the solid residuum 

 with dry rubbish, town ashes, charcoal, or other bases for forming 

 a solid substance ; the unwillingness, however, of farmers to pur- 

 chase this manure at a remunerative price to the manufacturers, 

 and often their refusal to pay for it at all, necessarily led to the 

 early closing of all works constructed for the purpose of its manu- 

 facture. 



In order to counteract the loss of valuable manurial ingredients 

 which, under the above processes, passed off with the liquid por- 

 tions of the sewage, recourse was next had to the use of chemical 

 reagents with the view of causing a precipitation of those fertilizing 

 ingredients which are held in solution, and for this purpose use 

 has been made of lime, sulphate of alumina, soluble phosphate of 

 magnesia, perchloride of iron, &c. ; but as none of these have been 

 successful in causing a precipitation of ammonia, or any other 

 manuring substance, it is needless to enter here into any further 

 details regarding these experiments. Suffice it to state that no 



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