56 THE CHEMISTRY OP THE FARM 



Sulphate of ammonium is a " special manure,** valu- 

 able solely for its nitrogen. It is an excellent manure 

 for corn crops and potatoes. Admixture with super- 

 phosphate and potassium salts is more necessary for 

 obtaining a profitable result with ammonium salts 

 than it is when nitrate of sodium is employed. 



If sulphate of ammonium is applied as a top-dressing 

 to arable land containing much carbonate of calcium, 

 some loss of ammonia is apt to occur from the vola- 

 tilisation of carbonate of ammonium ; this loss would 

 be greatly diminished by mixing the ammonium salt 

 with superphosphate, and by applying the dressing in 

 showery weather. Sulphate of ammonium generally 

 gives its best results when ploughed or harrowed in. 



The ammonia is converted into a nitrate in a few 

 days or weeks after the application of the salt to a moist, 

 fertile soil ; but nitrification may be much retarded by 

 dry weather. The use of sulphate of ammonium 

 is attended with some loss of lime to the soil, as both 

 the sulphuric acid, and the nitric acid subsequently 

 formed, unite with the lime of the soil, and the result- 

 ing calcium salts are more or less removed by drainage. 

 Ammonium salts produce little effect in soils destitute of 

 lime, as in such cases nitrification is much delayed ; the 

 evil may be cured by an application of lime in autumn. 



Nitrate of Sodium.— An enormous deposit of the 

 crude salt, containing much chloride of sodium, is found 

 in Peru. The nitrate sent to this country has been 

 purified by crystalHsation ; it contains 95 — 96 per cent, 

 of real nitrate, or 156 — 15'8 per cent, of nitrogen. The 

 most usual impurity is common salt. Inferior qualities 

 pf the nitrate occasionally contain sufficient perchloratg 



