118 AGRICULTURE 



nitrogen in the proportion of about 100 

 to 75, so that the former manure stands 

 practically always at a higher price per ton 

 than the latter. The basis of purity in the 

 case of nitrate of soda is generally 95 

 per cent., whereas sulphate of ammonia 

 can usually be purchased under guarantee 

 of 97 per cent, of purity. With these 

 figures before us, it is easy to calculate 

 what the relative amounts of nitrogen are 

 in the two manures. Nitrate of soda when 

 pure is a chemical substance, of which every 

 85 Ib. contain 23 Ib. of sodium, 14 Ib. of 

 nitrogen, and 48 Ib. of oxygen. Of these 

 three substances it is only the nitrogen that 

 interests us in the present connection, and 

 if 85 Ib. of nitrate of soda contain 14 Ib. of 

 nitrogen, 95 Ib. will contain 15-6 Ib. Seeing 

 that nitrate of soda is generally purchased on 

 a basis of 95 per cent, of purity, it means 

 that 100 Ib. of this manure, as commercially 

 obtainable, hold 15'6 Ib. of nitrogen. It 

 therefore follows that if 100 Ib. of com- 

 mercial nitrate of soda contain 15-6 Ib. of 

 nitrogen, a ton will hold 350 Ib. At the 

 present time, nitrate of soda costs about 

 10 per ton, so that the 350 Ib. of nitrogen 

 which the ton contains are being purchased 

 upon a basis of 6'9 pence per Ib. 



