34 PRACTICAL AGRICULTURAL CHEMISTRY [85-87 



it is fit for plant-food. The following three experiments 

 show how the different forms may be recognised. 



85. Test for Organic Nitrogen.— Mix together in a 

 mortar about as much shoddy (which has been cut up very 

 finely with a pair of scissors) as can be heaped up on a shil- 

 ling with about four times its weight of soda lime. Heat a 

 little of this mixture strongly in an ignition-tube (6). Am- 

 monia gas will be given off, which may be recognised by its 

 smell, and also by the fact that it turns moist turmeric 

 paper brown. 



Treat a little sulphate of ammonia in exactly the same 

 way as the shoddy. Ammonia will be given off more 

 readily than in the former case. 



Treat a little nitrate of soda in the same way. No am- 

 monia will be given off. 



Shoddy contains organic nitrogen, sulphate of ammonia 

 contains ammoniacal nitrogen, and nitrate of soda contains 

 nitric nitrogen. From the experiment just performed it will 

 be seen that the organic and ammoniacal forms are similar 

 in that they both give off ammonia when heated with soda 

 lime. They are distinguished from each other by the 

 experiment described in paragraph 86. 



86. Test for Ammoniacal Nitrogen.— Take three 

 test-tubes : in the first, place a little shoddy, cut up fine ; 

 in the second, a little sulphate of ammonia ; and in the 

 third, a little nitrate of soda. Half fill each test-tube with 

 potassic hydrate solution, and boil each in turn. The one 

 containing sulphate of ammonia will give off ammonia, which 

 may be recognised as before, whilst the other two will 

 not Ammoniacal nitrogen may always be recognised in 

 this way. 



87. Test for Nitric Nitrogen. — Take separate small 

 portions of sulphate of ammonia, shoddy, and nitrate of 

 soda in test-tubes and add water. Filter each and to the 

 clear liquid add a few drops of indigo solution ; then pour 



