MIXED FERTILIZERS 55 



neighbourhood as a dry powder. As the phosphoric acid 

 content is low, mineral phosphates are sometimes admixed. 



For countries with a plentiful seaboard the water-carriage 

 system supplies a simple solution of the sanitary difficulties, 

 since everything may be flushed into the sea, but such a 

 system provides no solution of the agricultural side of the 

 problem. The introduction of the sewage farm makes an 

 attempt to get over this difficulty, and utilize the manure for 

 food production. The conditions necessary for success are, 

 however, exceptional. Where there happens to exist a 

 suitable area of light soil, situated below the level of the 

 town supplying the sewage, with facilities for providing 

 a pipe with convenient gradients, the system may be a very 

 great success. When only clay land is available the amount 

 of land necessary becomes unreasonably large, and if too much 

 sewage is put upon the land it is ruined for years. Consider- 

 able skill is therefore necessary in management. In some 

 cases the sewage farms originally succeeded by an accident, 

 because the condition of affairs caused an approximation 

 to bacterial systems of purification. One of the great 

 difficulties of a sewage farm lies in the fact that it has to 

 take sewage according to the rate at which it is being produced 

 in the town, and not to suit the requirements of the farm. 

 If it were possible to entirely separate the rain-water of the 

 streets from the pure sewage, much of this difficulty would 

 be overcome, but it is very difficult to satisfactorily arrange 

 a farm on the system of always having to take manure, 

 whether it suits the crops or not. A not infrequent adjunct 

 to a successful sewage farm is a pig-breeding establishment, 

 as the pigs can eat up the large quantities of roots, etc., 

 grown on a sewage farm, which fastidious people do not 

 fancy. The hay crop is also a very important part of a 

 sewage farm, since large crops of succulent, if coarse, hay 

 can be obtained. 



The Sludge Precipitation System. —To prevent the 

 nuisance of crude sewage the idea arose of precipitating at 

 least some of the material as a sediment or sludge, and a large 

 variety of patent mixtures have been used for this purpose. 



