36 The Profitable Culture of Vegetables. 



In calculating the value of a manure from analysis all equi- 

 valents should be ignored, and a judgment formed solely 

 upon the nitrogen, soluble phosphates, and pure potash. If 

 these are satisfactory the insoluble phosphates may then be 

 taken into consideration, as some portions become slowly 

 soluble when buried in the soil, and they therefore have a 

 certain value, but not enough to influence a decision as to the 

 value of the active ingredients. 



It is very desirable that the purchaser should be able to 

 judge accurately of the comparative money-value of different 

 samples of ready mixed fertilizers, as well as to be able to 

 calculate what an equal fertilizing-value in materials would 

 cost if bought separately and mixed at home. This is done by 

 ascertaining the cost of a unit of each of the different fertilizing 

 constituents and adding these costs together. The unit is the 

 one-hundredth part of a ton, and the cost of a unit is known as 

 the " unit-value." The cost of a unit is arrived at by dividing 

 the market price of a ton of material by the percentage it con- 

 tains of the particular fertilizing constituent required. 



For instance, supposing it is desired to find the fair price 

 of a mixed mineral fertilizer containing 



Nitrogen 5 percent. 



Soluble Phosphates ... 17 



Insoluble ... 3 



Potash 6 



What has to be decided is, What is a fertilizer containing 

 the above ingredients worth? The percentages shown here 

 have nothing to do with the unit-value ; the item " nitrogen, 

 5 per cent." means that the mixed fertilizer in question con- 

 tains that amount of nitrogen, and the object is to ascertain 

 what that amount of nitrogen would cost if bought in the form, 

 say, of sulphate of ammonia or nitrate of soda. 



The nitrogen in this fertilizer will be derived from sulphate 

 of ammonia, which contains ammonia equal to 20 per cent, 

 nitrogen, and costs at present market prices about 12 per 

 ton; the unit-value is ascertained by dividing 12, the price 

 of a ton of sulphate of ammonia, by 20, the percentage of the 

 nitrogen it contains; the result is 12s., which represents the 

 unit-value of nitrogen derived from sulphate of ammonia. 



