303 



The action of the manure is naturally most marked in 

 the year of application but is not by any means confined 

 to this year. 



During 1906 from 1500 to 2000 tons were imported 

 into Egypt costing from 280 to 320 P.T. per ton, with a 

 guarantee of from 16 to 18 per cent, of phosphoric acid 

 soluble in citrate solution. It is applied chiefly to the 

 cotton crop. The same amount was imported during 1907, 



BASIC SLAG. 



The heavy grey-black powder sold under this name is 

 a manure of only some twenty years' standing and is a 

 bye- product in the preparation of steel by the Bessemer 

 process from pig-irons rich in phosphorus. During the 

 process this phosphorus is oxidised and enters into combi- 

 nation with the lime and magnesia of the basic lining of 

 the vessel in which the operations are conducted forming 

 a slag. At one time this w r as thrown on the rubbish heap 

 as useless ; it is now very finely ground and in this state 

 forms one of the cheapest and most important of phos- 

 phatic manures on the market. The composition of basic 

 slag naturally varies considerably. Its main ingredients 

 are lime CaO and phosphoric acid P 2 5 . The CaO 

 is present as free lime and combined with the P 2 5 as 

 tetracalcic orthophosphate Ca t P 2 9 = 4 CaO, P 2 5 with 

 considerable quantities of the oxides of iron and mag- 

 nesium, some silica as silicate and a little sulphide. The 

 amount of phosphoric acid P 2 5 - may be anything from 

 10 to 20^ so the manure should always be bought on 



