48 FARM MANAGEMENT 



always best to postpone mixing them till just 

 before they are to be sown. 



Buying Manures. — When buying artificial 

 manures the buyer is legally entitled to receive 

 a guarantee from the seller that the manure con- 

 tains a certain percentage of whatever ingredi- 

 ent the manure is bought for. Neither this nor 

 the price per ton, however, decides which is the 

 cheaper of two manures of the same kind. To 

 determine this divide the price per ton in each 

 case by the percentage of, say, nitrogen the 

 manure is said to contain, and the result is the 

 price of one per cent, of nitrogen in the manure, 

 or the **unit value," as it is termed. Knowing, 

 then, the unit value of nitrogen in each of the 

 manures, you know which is the cheaper of the 

 two. 



This valuation by unit values is of particular 

 use in determining the value of special com- 

 pound manures that manufacturers often sell. 

 Such a manure will be guaranteed to contain 

 certain percentages of nitrogen, phosphates and 

 potash, and if these percentages are multiplied 

 by their unit values, as sold in ordinary artificial 

 manures, and 7^. (id. per ton added for mixing, 

 y^ou know what the special manure is really worth. 



