OILCAKES— PHOSPHATIO SLAG 59 



on heavy land ; their effect is thus spread over several 

 years. The finer the bones have been ground the 

 more immediate is their effect. Bones are usually 

 employed for pasture, and for turnips. 



Oilcakes. — Cakes of little or no value for feeding 

 purposes are used when ground as manure ; their 

 value as manure is rather considerable, as they contain 

 a good deal of nitrogen, with phosphates and potash 

 (see p. 219). On light soils rape cake is often used as 

 a manure for barley. 



Phosphatic Slag and Ground Phosphates. — Some 

 phosphates when finely ground may be successfully 

 employed as manure without previous conversion into 

 superphosphate. The phosphate at present most used 

 for this purpose is Thomas' slag. Phosphatic slag is 

 of various qualities, containing 10 — 22 per cent, of 

 phosphoric acid, with a considerable excess of lime. 

 The soils most suitable for manures of this class are 

 those rich in humus and poor in carbonate of calcium ; 

 these being the conditions (presence of humic and 

 free carbonic acid) most favourable to the solution of 

 phosphate of calcium. Moorland and pasture soils are 

 especially suitable for such treatment. All undis- 

 solved phosphates must be employed in extremely fine 

 powder. Good basic slag is generally sold with a 

 guarantee that 80 per cent, of the powder shall pass 

 through a sieve having 10,000 meshes in a square 

 inch. 



Thomas' slag is an effective manure for swedes ; it 

 is especially excellent as a dressing for old pastures, 

 on which it generally develops a considerable growth 



