136 Fertilisers [pt. iii 



no diminution in amount^ but some action nevertheless 

 goes on and calcium occurs in the solution. In conse- 

 quence ammonium sulphate is much in favour in tropical 

 countries and is used in the West Indies for the sugar 

 cane. Of course as soon as it has become nitrified it is 

 liable to sink to greater depths, but in an acid soU, or 

 wherever nitrification is not \^ery active, it remains in 

 the surface layers. Here it encourages a surface rooted 

 vegetation, and for this reason it is used on lawns where 

 only the fine shallow rooting grasses are desired. 



This tendency to remain in the surface layers has 

 sometimes given sulphate of ammonia an advantage 

 over nitrate of soda on sandy soils not deficient in 

 lime^. 



Commercial sulphate of ammonia contains about 20 

 per cent, of nitrogen ; it is the most concentrated of aU 

 these manures. Its pre-war price was about 13 per ton 

 f.o.r. : 1 per cent, per ton (or 1 unit) therefore cost 135. 

 and a poiuid of nitrogen in this form cost Id. During 

 the war its price was fixed by the Government : it varied 

 from 15. 5s. to 16. 15s. per ton. A little free acid is 

 usually present : if there is less than 0*025 per cent, the 

 sample is known commercially as " neutral." 



Ammonium nitrate 



This is much more concentrated than the ordinary 

 nitrogenous fertilisers, containing in the pure state no 

 less than 35 per cent, of nitrogen, m hich is more than 

 double the quantity in nitrate of soda. It has the dis- 

 advantage of being deliquescent and highly soluble, and 

 these properties interfered with its use in practice. It 



^ A suitable test is given on p. 228. 



* An instance is quoted in Bied. Centr., 1908, xxxvii. 585. 



