158 MANURES. VII. 



slag as to their solubility: the following numbers were 

 given : 



Relative solubility in cold water after 48 hours. 

 " Basic super." Basic slag. 



Portion soluble ... ... 66'80 6' 60 



Portion insoluble (after burning) 33'20 93*40 



Soluble lime ... ... 22-28 4-70 



No phosphate soluble in water. 



In the first place, since phosphoric acid is the valued ingre- 

 dient in both manures and in neither case was any dissolved 

 in water, the comparison as a criterion of their manurial value 

 is useless. Next, the " basic super." is highly hydrated, while 

 the basic slag is practically anhydrous, and the " portion 

 soluble" in the table evidently includes the water present (for 

 it is the difference between 100 and the "portion insoluble, 

 after burning"). Moreover, of the " portion soluble" a large 

 proportion consists of the comparatively worthless calcium 

 sulphate, in which state also much of the "soluble lime" exists. 



The new 7 manure may probably produce a better effect than 

 superphosphate 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 solu- 

 bility 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 under- 

 stand 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 ing-iron or cast-iron, in which are 

 numerous impurities (as is seen from the subjoined analysis), 

 removing these impurities, including "almost the whole of the 

 carbon, by refining and puddling, and so obtaining vroui/Jit- 

 iron, which is almost pure iron, and lastly causing this, after 

 it had been rolled out into thin bars, to combine with the 



