v. ] VAL UA TION OF MANURES. 



43 



ton; or if it contained 30 units at the same price per 

 unit, it would be 6 per ton, and so on. It is on this 

 basis that the valuation of manures has been 

 established. Experience however has shown that 

 great care is necessary in making these valuations. 

 One difficulty exists in fixing the price per unit, but 

 this is necessarily subject to the variations of the 

 market and is a fair matter for contract as between 

 buyer and seller. 



82. It will be easily understood from what has been 

 said that the method of valuation indicated above 

 (77) is somewhat defective, for whilst the bi-calcic 

 phosphate is a most useful part of the manure, the valuer 

 pays attention almost entirely to the mono-calcic phos- 

 phate, because the estimation of the former is somewhat 

 difficult, and its value has not yet been fully appreciated 

 by chemists. This is a matter of considerable impor- 

 tance ; for so long as the present system of valuation is 

 maintained, so long manufacturers will be compelled 

 to sell, and farmers to buy, over-manufactured 

 manures, having a higher degree of solubility than 

 is consistent with the healthy growth of our crops. 

 On the other hand, the production of a form of phos- 

 phate whose high value is well known to the farmer 

 and the manufacturer, is now rendered practically 

 impossible. The magnitude of this question will be 

 more fully realized when you consider that the sales 

 of superphosphate represent an annual outlay of be- 

 tween two and three million pounds sterling. 



83. There is another class of artificial manures 

 which are chiefly distinguished by the presence of 

 nitrogenous compounds. Peruvian guano is 

 one of the richest manures of this class. Its value 

 depends not only upon the large quantity of ammonia 

 which it contains, but upon the fact that it is mixed 

 with various other valuable fertilizers. Guano is the 

 dung of sea-birds, which has accumulated for many 

 centuries in a climate where there is but little rain to 



