CHAPTEE IX. 

 THE ANALYSIS AND VALUATION OF MANURES. 



IN this chapter, before discussing very briefly some] of the methods 

 used for the determination of the valuable constituents 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 merely 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 SUPEKPHOSPHATE. 



Per cent. 

 Monocalcium phosphate ...... 



(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 (vide 

 p. 147), but may perhaps with advantage be repeated here. 



By " monocalcium phosphate " in the above analysis is meant all 

 the phosphates soluble in water, expressed as monocalcium phosphate 

 (not, as would be correct, as CaH 4 P 2 8 , but totally falsely as CaP 2 O 6 , 

 which is the formula for calcium metaphosphate). Consequently, the 

 percentage amount of "monocalcium phosphate," in order to give the 

 equivalent amount of "bone phosphate," i.e., Ca 3 P<,0 8 , must be multi- 

 plied by 120 + 62 + 128 = 310, and divided by 40 + 62 + 96 = 198. 



By " insoluble phosphate " in the analysis, is meant the total of tri- 

 calcium (and trimagnesium) phosphate, Ca 3 P 2 O 8 (insoluble in solution of 

 ammonium citrate), and dicalcium phosphate, Ca 2 H 2 P 2 O 8 (= CaHP0 4 ), 

 together with the phosphoric acid in combination with iron and alu- 

 minium (soluble in solution of ammonium citrate), all expressed in terms 

 of tricalcium phosphate. The phosphoric acid soluble in ammonium 

 citrate solution is known as "reverted," "retrograde," or "reduced". 



The " hydrated sulphate of lime " obviously refers to the compound 

 identical in composition with gypsum, CaSO 4 .2H 2 O. 



" Organic matter and water" requires no explanation ; it is loss on 

 ignition after deducting the water contained in the "hydrated sulphate 

 of lime," which would also be expelled; why this allowance is made 



(170) 



