EGYPTIAN AGRICULTURE. 



employed for its utilisation. The first is sewage irrigation, 

 by means of which it is poured on to the land which is 

 specially arranged for the purpose. The second is that 

 known as precipitation, etc. In Egypt where no system 

 of drainage exists and the material is removed from cess- 

 pits by means of pumps, the latter only is used. 



Mechanical filtration removes the insoluble suspended 

 matter which it contains, and the medium usually employed 

 is charcoal, either alone or mixed with sand, burnt clay, 

 etc. By chemical filtration, however, practically the whole 

 of the phosphoric acid is removed, and of all substances 

 employed lime is probably the most common on account 

 of the ease with which it can be obtained and its low 

 price. While the substance as obtained contains a very 

 large proportion of the phosphoric acid of the sewage, the 

 nitrogen and potash present in the liquid part are not re- 

 tained. In addition to lime, a great many other substances 

 are employed, either alone or in conjunction with it or 

 with one another. Sulphate of alumina, perchloride of 

 iron, sulphate of iron, etc., etc., are employed, and in a 

 well known process, the A. B. C., a mixture of various 

 proportions of alum, charcoal, clay, lime, blood and 

 alkalies is used. Only partial purification, however, is 

 obtained. The sludge was at first allowed to dry by exposure 

 to the atmosphere, but rapid decomposition was set up and 

 the filter came into use which at once removed a very 

 considerable amount of the water. As regards the actual 

 manurial value of the sludge, considerable differences of 

 opinion exist, and to its physical character have been 

 attributed the poor results which have been obtained. The 



