226 SOILS AND MANURES 



This difficulty has been surmounted by the introduction 

 of a basic lining consisting of lime, or dolomite powder 

 a mixture of lime and magnesia and the addition of 

 lime to the molten pig iron. With this improvement, intro- 

 duced by Thomas and Gilchrist in 1879, the process can be 

 applied to products containing from 2 to 4 per cent, of 

 phosphorus, and it is the spent slag from this part of the 

 process that is ground up and sold as manure. 



When the converter has been properly lined and pre- 

 pared, the molten pig iron is introduced, and the air 

 blast started. The crude product may contain from 

 3 to 6 per cent, of carbon, and from 1 to 2 per cent, 

 of silicon, besides phosphorus, sulphur and other im- 

 purities, all of which, together with some of the iron 

 and manganese, undergo oxidation. A considerable rise 

 of temperature takes place in consequence, the lime melts 

 and unites with the oxides of phosphorus and silicon, and 

 the products, being lighter than the iron, rise to the 

 top. The carbon monoxide, formed by the oxidation of 

 the carbon, escapes and becomes ignited on contact with 

 the air, and the characteristic flame of the gas is seen 

 playing on ttie surface until the iron is completely de- 

 carbonised. The operation, which only occupies about 

 15 minutes, is then stopped and the slag is poured off. 



In the illustration l the converter is shown turned up 

 (Fig. 29) with the " blow " in operation; Fig. 30 shows 

 the converter turned down after the "blow" is finished, 

 and the slag being poured into the " ladle " below. When 

 cold it presents the appearance of a hard massive black 

 cinder. In order to prepare it for use as manure, it is sub- 

 jected to a very elaborate process of grinding, for which 

 special machinery has been invented. It is first broken 

 into small pieces under stamps, then crushed under heavy 



1 Copy supplied by Chemical Works, late H. & E. Albert, London. 



