2 INTRODUCTION 



dissolving bones in sulphuric acid, and at a time when his experiments 

 with dissolved bones, and later with dissolved rock phosphates, at 

 Rothamsted focussed attention very effectively on the superior value 

 of water soluble phosphates. The Rothamsted experiments seem to 

 have very rapidly convinced those farmers who followed such develop- 

 ments of the superior efficiency of water soluble phosphates, although 

 attention was drawn at intervals to experiments which apparently 

 showed insoluble phosphates to be as effective as water soluble phos- 

 phates. 



BASIC BESSEMER SLAG 



The introduction by Thomas and Gilchrist in 1878 of their process 

 for removing phosphorus from the molten pig-iron provided in the 

 resulting slag a new source of phosphate for agricultural purposes. 



The presence of phosphorus in steel, except in very small amounts, 

 renders the metal brittle and unfit to use for many manufacturing 

 purposes. Most of the iron ores in this country are highly phos- 

 phatic, and until the coming of the Thomas and Gilchrist process it 

 was not possible to remove phosphorus from the pig-iron and so 

 produce a good quality of steel. 



The first step in the manufacture of steel is the conversion of iron- 

 ore into pig-iron under the reducing conditions which exist in the 

 hearth of the blast furnace. Such reducing conditions are essential 

 for the recovery of iron from the ores, but they prevent the oxidation 

 of phosphorus, which therefore passes into the pig-iron. 



The conversion of non-phosphatic pig-iron to steel is carried out 

 in a Bessemer vessel with a siliceous lining acid process. If phos- 

 phorus is present in the pig-iron phosphoric acid is formed, which, 

 being unstable in the presence of an excess of iron, reverts to phos- 

 phide of iron, which is not removed in the slag. 



The Thomas and Gilchrist modification of the Bessemer process 

 consists in lining the furnace with a basic material instead of a 

 siliceous lining, and of adding suitable quantities of lime to the molten 

 iron. The phosphoric acid formed combines with the lime producing 

 a stable phosphate of calcium, which is removed in the slag which 

 floats on top of the molten metal in the converter. 



The process was first tried on a large scale at Messrs Bolckow 

 Vaughan and Co.'s Eston Works, in 1879, and a copy of the record 

 which illustrates the manufacture of the first Basic Slag is reproduced 

 in Table I by the courtesy of Mr Daniel Sillars, chief chemist to 

 Messrs Bolckow Vaughan and Co. 



