263] Valuation of Manures by Analysis 



The price may be added up in this manner : 



155 



The market price of such a manure would therefore be 

 £5 5 s - &i^- P ms tne cost °f m ixing the ingredients. 



263. Valuation of Mineral Phosphates.— In this 

 country, now that the coprolite beds are almost used up, the 

 use of mineral phosphates in the raw state as manures is quite 

 exceptional. Therefore the valuation is based on the readiness 

 with which they are converted into superphosphate and on 

 the quality of that product when made. The principal 

 impurities which influence superphosphate manufacture are 

 the oxides of iron and aluminium, carbonate of lime, and 

 fluorides. The extent to which these impurities are detri- 

 mental is partly shown in the following table, which gives the 

 amount of pure H 2 S0 4 , oil of vitriol S.G. i"6, and oil of 

 vitriol S.G. 1*55 absorbed by 100 parts of each substance : 



Against this waste of sulphuric acid must be placed the fact 

 that a certain amount of CaC0 3 is somewhat beneficial. The 

 carbonic acid gas escaping within the mass promotes spongi- 

 ness and lightness in the manure, and facilitates drying. 



In the case of CaF 2 , the whole of the HF does not escape, 



