PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 587 



These results have been verified by an expenditure of £40,000 at the Stan- 

 ley' Bridg"e works in London, and by experience witli processes of reduc- 

 tion by lime, sulphate of alumina and charcoal, by ag-itation with or 

 filtration through charcoal, and by niagnesian salt, detailed in the Metro- 

 politan Drainag-e Report of 1857. 



The mechanical obstacles to the solution of this problem of utilization 

 assume a very diflferent aspect, in all cases which admit of processes of 

 direct agricultural irrigation b}-- sewage flow. In cases of extension and 

 long continued application, very favorable results are reported. 



The Vettabbia, a canal which receives the sewage water of Milan, dis- 

 charging into the river Lambro, ten miles distant, is arranged so as to 

 irrigate a large extent of meadow land, with a remarkable result in pro- 

 diictiveness. These meadows yield a net rent of $40 (£8) per acre, beside 

 paying taxes, &c. They are mowed four times a year for stable feeding, 

 and yield three crops of hay, with pasturage after August. 



At Edinburgh, for forty-five years, several hundred acres of successive 

 ])lateaus have been irrigated from ponds or tanks which receive the Old 

 Town sewage water, in part. "The practical result is that land which let 

 formerly at from forty shillings to six pounds per Scotch acre, is now let 

 annually for from thirty to forty pounds, and that poor sandy land on the 

 seashore, which might be worth two shillings and six pence per acre, lets 

 at an annual rent of from fifteen to twenty pounds; on lands near the city 

 twenty-five pounds per acre is the net annual income due to the sewage 

 water; 17,920 gallons, containing five hundred weight of dissolved and 

 suspended matter, are equal in fertilizing power to two and a half hundred 

 weight of guano, or fifteen tons of farm yard manures, and cost in appli- 

 cation twelve shillings and nine pence in comparison with three pounds 

 for the latter, the economy being greater with an increased scale of irriga- 

 tion." Drainage and Sewage of Towns. 



At Mansfield, AVilleston, Ashburton, Chatsworth and other English 

 towns; at Berlin, in Sweden, Tuscany, Switzerland, Flanders, and in vari- 

 ous other countries of Europe; in Asia, Africa and South America, irriga- 

 tion has been practiced from time immemorial for agricultural purposes. 



A valuable paper on this subject was contributed to the Farmers' Club 

 of the American Institute by K. L. Pell, Esq., and. is given in pages B36 

 to 360 of the Transactions of 1863. On the application of liquid manure 

 Mr. Pell says: 



" Not only is the produce increased, but offensive emanations are entirely 

 prevented by a greater dilution with water, and more frequent applications 

 of the liquid to plants. - These conclusions were early corroborated by an 

 able agriculturist, the late Mr. Oliver, of Lochend, who held a portion of 

 the irrigated meadows near Edinburgh, and who complained that the 

 sewer water, as there obtained, was far too highly charged with manure 

 fur its best application, and that such tenants as himself were prevented 

 from improving the system by the want of water for proper dilution and 

 of means necessary for more frequent applications of liquid manure. He 

 was so convinced ol' the necessity of greater dilution that he caused water 

 to be pumped by steam for the purpose. 



