148 



BASIC SUPEKPHOSPHATE BASIC SLAG 



Eeference may here be made to a recently patented manure to 

 which the contradictory name of basic superphosphate has been given. 

 This is a product obtained by adding 15 parts of slaked lime to 85 

 parts of good superphosphate, thoroughly mixing the two, and allowing 

 them to stand at least twenty-four hours. A dry, bulky powder is thus 

 produced, which, it is claimed, has many advantages over basic slag. 1 



The phosphoric acid of the superphosphate, is, of course, rendered 

 insoluble in water by this treatment, though the phosphate of lime thus 

 produced is doubtless more easily dissolved by soil solvents than that 

 existing even in finely ground mineral phosphates. 



The new manure may probably produce a better effect than super- 

 phosphate upon soils deficient in calcium carbonate or other basic 

 material, but it would certainly seem preferable either to use basic slag 

 on such soils, or to apply the lime and superphosphate separately and 

 thus secure the advantage of their more uniform distribution in the 

 soil which their solubility in water (while separate) ensures. 



Basic Slag, or Thomas Phosphate, is now one of the cheapest 

 and best sources of phosphoric acid. It results as a bye-product in 

 the manufacture of steel from pig-iron rich in phosphorus. In order 

 that the student may clearly understand its origin, it will perhaps be 

 advisable to briefly review the chemistry of the processes used in the 

 production of steel. 



Until 1856 steel was made by the laborious and expensive process 

 of first obtaining pig-iron or cast-iron, in which are numerous impuri- 

 ties (as is seen from the subjoined analyses), removing these impurities, 

 including almost the whole of the carbon, by refining and puddling, 

 and so obtaining ivr ought-iron, which is almost pure iron, and lastly 

 causing this, after it had been rolled out into thin bars, to combine with 

 the requisite quantity of carbon by the process known as cementation, 

 in which the bars of wrought-iron are heated in a closed iron case with 

 powdered charcoal for several days. The iron under this treatment 

 was converted into steel. The process was so costly and tedious that 

 steel commanded a very high price and was only used for special 

 purposes. 



Analyses of pig-iron, wrought-iron and steel : 



Hughes, Jour. Soc. Chem. Ind., 1901, 325. 



