33 



COST AND VALUATION OF SULPHATE. 



It cannot be too clearly understood that it is only the 

 nitrogen that is of value in sulphate of ammonia. Hydrogen, 

 oxygen, and sulphur are all necessary for plant growth, it is 

 true ; but they are supplied so freely by natural means that 

 there is never any need to apply them as manure. We 

 may therefore fairly consider that the whole price paid for 

 sulphate of ammonia is given for the nitrogen; and. we can 

 thus easily find out what the nitrogen costs per pound. For 

 instance, a recent quotation for sulphate of ammonia is 

 10 2s. 6d. per ton, containing 24 per cent, of ammonia. 



A ton will contain 2240 x = 537'6 Ibs. of ammonia, 



100 



equal to 442-7 Ibs. of nitrogen. The price of ammonia in 

 the manure is, therefore, 10 2s. 6d. -f- 537*6 = 4^d. per Ib. ; 

 and of nitrogen, 10 2s. 6d. ^ 442-7 = 5*d. per Ib. 



Calculations of this kind may be used for comparing one 

 manure with another. For instance, nitrate of soda contains 

 about 15-65 per cent, of nitrogen, equal to 19 per cent, of 

 ammonia ; that is 350*5 Ibs. of nitrogen per ton, equal to 

 425-6 Ibs. of ammonia. The price at the time of writing is 

 about j 153. per ton, at which price nitrogen costs j 155. 

 -^ 35'5 = 5H- P er lt>. ; and ammonia, j 155. -f- 425-6 = 

 4*d. per Ib. 



A more usual way of comparing the cost of nitrogen in 

 different manures, and a more convenient one, is by calculat- 

 ing the cost of nitrogen or ammonia per unit that is, the 

 price per ton of the manure for each i per cent, of ammonia 

 or nitrogen. For instance, in the example taken above the 

 sulphate of ammonia is said to contain 24 units of ammonia 

 or igf units of nitrogen. The price per unit of ammonia is 

 therefore IQ 2s. 6d. -f- 24 = 8s.. $d. ; while a unit of 

 nitrogen costs 10 2s. 6d. -f- igf = los. 3d. Similarly, 

 the nitrate of soda is said to contain 15-65 units of nitrogen, 

 or 19 units of ammonia; the price of the former being nearly 

 95. i id. per unit, that of the latter 8s. 2d. per unit. In actual 

 working, this system of estimating the cost per unit is very 

 simple and helpful in comparing the relative costs of manures; 

 for by it, and taking into account also the suitability of two 

 manures for any given purpose, we can decide on their com- 

 parative economy. It will be easily realized that nitrogen is 

 sometimes cheaper in one manure, sometimes in another, 

 according to variations in the market quotations. Very 

 often one comes across a tendency to buy a manure because 

 it is at a low price per ton ; but this may not be the cheapest 

 manure. The cost per unit of nitrogen, or whatever of 

 value the manure contains, may be greater than that in 

 another manure at a higher price per ton. 



At the prices mentioned above, it will be seen that nitrogen 

 in sulphate of ammonia is slightly more expensive than in 



c 



