64 CHEMICAL FERTILIZERS 



and permits of the use of large quantities of scrap. In some 

 works the Talbot process of a large tilting furnace of cylin- 

 drical form is also used. The resulting basic slag, whatever 

 may be the process of its manufacture, is run out into trucks, 

 cooled and broken up, its subsequent history being described 

 on p. 120. Efforts have been made to improve the quality 

 of the slag from the manurial point of view by adding to it 

 some quantities of rock phosphate. Indian apatite contains 

 too much iron for siiperphosphate manufacture, but has 

 been used to enrich Indian basic slag which is poor in 

 phosphorus. No doubt this method will increase the 

 percentage of phosphorus in the slag, but whether it is 

 economically justifiable remains yet to be found out. 



The Zinc Smelting Industry gives rise to sulphuric 

 acid as a by-product which is used to manufacture superphos- 

 phate. The production of sulphuric acid from this source 

 is likely to increase to such an extent as to affect vitally the 

 supplies of superphosphate (see p. 128). 



Various small metal industries give rise to by-products of 

 value as fertilizers. Steel cylinders are often annealed and 

 hardened with the aid of powdered charcoal ; after a time 

 the charcoal burns away leaving an ash containing potash. 

 Case hardening requires many mixtures containing potassium 

 ferrocyanide, bone meal, etc. The object of such processes 

 is partly physical and partly chemical but they yield residues 

 containing potash, phosphates, etc. Without a knowledge 

 of local customs, the value of such products cannot be 

 gauged. 



The Recovery of Nitrogen, Phosphorus and Potas- 

 sium. It is interesting to note that by means of the Mond 

 gas process, combined with the blast furnace and basic steel 

 processes, we now possess means for recovering all nitrogen, 

 phosphorus and potassium from any low-grade refuse, and 

 converting them into forms suitable for use as fertilizers. 

 Any refuse, either human, animal, vegetable or mineral, if 

 distilled without previous drying, with steam at moderately 

 high temperatures, will yield almost all its nitrogen as 

 ammonia, and produce a combustible gas. The ammonia 



