IX. THE ANALYSIS AND VALUATION OF MANURES 171 



for mere water of crystallisation in the case of calcium sulphate and 

 no allowance for the necessary water of constitution of the monocal- 

 cium tetrahydrogen phosphate, CaH 4 P 2 O 8 , it is difficult to understand. 



"Alkaline salts" is another unsatisfactory item; it is hard to say 

 exactly what it means. 



" Silica " usually represents the matter insoluble in acids and often 

 consists mainly of real silica, SiO 2 , though it may contain other mineral 

 fragments. 



A much more scientific and in every respect more satisfactory way of 

 reporting such an analysis, adopted in more recent work, is as 

 follows : 



Per cent. 

 Total phosphorus pentoxide ......... 



( Soluble 



of which is I " Reverted," "reduced," "retrograde," or, better, 



j " citrate soluble " 

 I Insoli 



Insoluble 

 Sulphur trioxide . 

 Loss on ignition . 

 Potash (if any) 



In the case of nitrogenous manures it is often the practice to give 

 the nitrogen as equal to per cent of ammonia ; if the percentage of 

 nitrogen is given as well, this plan is perhaps permissible, but it 

 would be much more intelligible to give the latter than the former. 

 The percentage of ammonia equivalent to the nitrogen present should 

 therefore not be given alone, especially in analyses of organic manures 

 or those containing nitrates. If the nitrogen content be stated, no 

 error as to its state of existence can be conveyed, and its equivalent in 

 ammonia or nitrogen pentoxide is easily calculated, since N = NH 3 



N O 



= p 5 or 14 of nitrogen correspond to 17 of ammonia or 54 of 

 A 



nitrogen pentoxide. 



The most complete way would be as follows : 



Per cent. 

 Total nitrogen . . . . . . 



I Ammoniacal nitrogen .... 

 of which is J Organic nitrogen . 



( Nitric nitrogen ..... 



The analysis of a manure is usually directed to the determination 

 of the amounts of one or more of the three substances, nitrogen, 

 phosphorus pentoxide, or potash present, and to the detection of the 

 presence, and, if necessary, the determination of the amount, of any 

 possibly harmful or objectionable ingredients. 



The following table gives a list of most of the commercial manures, 

 with their valuable and objectionable ingredients : 



