16 PLANT PRODUCTS 



a piece of blue litmus paper. When heated it gives up the 

 small amount of water which it contains, and then proceeds 

 to undergo a regular and complete decomposition. At first 

 sulphate of ammonia decomposes into ammonia and 

 ammonium hydrogen sulphate, then splits off some sulphur 

 tri-oxide, which reacts as an oxidizing agent, giving off 

 free nitrogen and sulphur dioxide. The sulphur dioxide, 

 together with the water, and some of the free ammonia, 

 then again combine and produce ammonium hydrogen 

 sulphite. These reactions can easily be perceived when 

 ammonium sulphate is slowly heated in a test-tube. The 

 water coming off will at first condense in the colder and upper 

 part of the test-tube ; further heating results in giving off 

 a smell of ammonia, and in the formation of a sublimate in 

 the colder part of the test-tube. If, after cooling, one or 

 two drops of hot water be added to the contents of the test- 

 tube, a smell of sulphur dioxide is at once perceived, because 

 the ammonium hydrogen sulphite is not a very stable 

 body, but dissociates with hot water. The ultimate result 

 of heating sulphate of ammonia is that the water, ammonia, 

 and sulphuric acid are driven off, and nothing left behind 

 but some mineral impurity which is mostly a trace of soil 

 or iron oxide. 



When sulphate of ammonia comes into contact with an 

 alkali or strong base, the sulphuric acid combines with the 

 alkali or base, and the ammonia is set free and diffuses into 

 the atmosphere. It is for these reasons, that sulphate of 

 ammonia should never be mixed with lime, wood ashes, 

 or basic slag. However, very few soils are so calcareous 

 that the clay and humus do not greatly preponderate over 

 the lime, so that the ammonia is more readily fixed by the 

 clay and the humus than it is driven off by the lime materials. 

 Sulphate of ammonia will take three weeks of very good 

 weather to nitrify all the ammonia added to the soil. 

 Nitrification, though very slow in the winter, produces some 

 nitrate which is lost by drainage, though such loss is not 

 sufficient to condemn the winter application of sulphate 

 of ammonia. On general grounds sulphate of ammonia 



