173 



CHAPTER VIII. 

 THE ANALYSIS OF MANURES. 



IN this chapter, before discussing very briefly some of the 

 methods used for the determination of the valuable consti- 

 tuents of manures, a short account of the usual methods of 

 expressing the results of a chemical analysis of manures will 

 be given. Some of these methods are purely conventional and 

 involve the use of certain terms which are no longer used in 

 the same sense in modern scientific nomenclature. Take, for 

 example, a superphosphate ; the usual old-fashioned method of 

 expressing its composition is as follows : 



ANALYSIS OF A SUPERPHOSPHATE. 



% 

 Soluble phosphates 



(equal to bone phosphate rendered soluble) ... 



Insoluble phosphate 



Hydrated sulphate of lime 



Organic matter and water 



Alkaline salts 



Silica ... 



The explanation of some of these terms has already been 

 given (v. p. 156), but may perhaps with advantage be repeated 

 here. 



By " soluble phosphates" in the above analysis is meant all 

 the phosphates soluble in water, expressed as mono-calcium 

 phosphate (not, as would be correct, as CaH 4 P 2 8 , but totally 

 falsely as CaP 2 O, ; , which is the formula for calcium meta- 

 phosphate). Consequently the percentage amount of " soluble 

 phosphates," in order to give the equivalent amount of " bone- 

 phosphate," i.e., CaP 2 8 , must be multiplied by 120 + 62 + 128 

 -310, and divided by 40 + 62 + 96-198. 



By " insoluble phosphate" in the analysis is meant the total 

 of tricalcium (and trimagnesium) phosphate, Ca 3 P 2 O 8 (insoluble 



