VALUATION OF MANURES. 181 



In sulphate of ammonia, containing, say, 24 - 5% of " am- 

 monia," equal to 20'2% nitrogen, if its price be taken at 12 

 per ton, nitrogen costs 

 12 x 20 x 100 



2240x20-2 ' ' 



12 x 20 



or its value "per unit" = - = ll'83s. = lls. lOd. 



.20' 2 



The two methods of expressing values are related to each 

 other in a simple manner. It is evident that the price " per 

 unit," since it refers to the price per ton for each per cent. 

 of the constituent in question, is really the price of -^^ of a 

 ton of the actual manurial constituent. In other words it is 

 the price of 22-4H). Obviously the price per ft>. multiplied by 

 22 -4 will give the equivalent price " per unit." 



In a similar way the value of phosphorus pentoxide and 

 potassium can be calculated from the market prices of the 

 various phosphatic and potash manures. As in the case of 

 nitrogen, the values obtained vary in the case of different 

 manures. 



Tables are sometimes published giving the value of the 

 three principal manurial substances per unit in various com- 

 mercial manures. The table on the following page, calculated 

 from one given in the Transactions of the Highland and 

 Agricultural Society of Scotland, 1900, may serve as an 

 example. 



The figures in brackets after the name of the manure indi- 

 cate the trade guarantees. 



In ordinary tables of this kind the values per unit of 

 "ammonia" and "phosphates" (i.e., Ca 3 P 2 8 ) are usually 

 given, and not those of nitrogen and phosphorus pentoxide, 

 as in the following table. The latter plan certainly appears 

 preferable, except on the ground of custom, since such sub- 

 stances as nitrate of soda or any organic manure contain 

 none of their nitrogen in the form of ammonia; and, similarly, 

 superphosphate and basic slag contain most of their phos- 

 phorus pentoxide in forms other than tricalcium phosphate. 

 Perhaps the same argument applies to the other manurial 

 constituent potassium (though to a less degree), since in 

 some manures it exists as chloride. 



