88-90] THE MIXING OF MANURES 35 



in strong sulphuric acid until the volume of liquid is 

 about doubled. In the case of shoddy and sulphate of 

 ammonia no change will take place. With nitrate of soda 

 the indigo will be bleached. This operation may be used 

 as a test for nitrates in manures. 



The Mixing of Manures 



88. In mixing manures care must be taken not to mix 

 two substances which act chemically upon each other. 

 Attention has already been called to the fact that lime acts 

 upon superphosphate (82), rendering the phosphoric acid 

 insoluble in water ; and since basic slag contains a certain 

 quantity of lime it should not be mixed with super- 

 phosphate. Other substances which should not be mixed 

 are shown in paragraphs 89 and 90. 



89. Action of Superphosphate on Nitrate of 

 Soda. — Mix equal quantities of superphosphate and 

 nitrate of soda in a mortar. Notice the peculiar smell of 

 the mixture. Heat a small quantity in an ignition- tube. 

 It will give off brown fumes. The reason is that super- 

 phosphate contains a certain amount of free sulphuric acid 

 which is used in its manufacture, and tlus acts upon the 

 nitrate of soda, setting free nitric acid, which is recognised 

 by its smell and the brown fumes formed when it is heated. 

 Now since nitric acid contains nitrogen, and is volatile, it 

 will pass off into the air, and so nitrogen will be lost. 

 Further, nitric acid is a very corrosive substance, and will 

 attack the bags in which manure is stored. Hence super- 

 phosphate and nitrate should never be mixed before ap- 

 plying them to the land. 



90. Action of Slag on Sulphate of Ammonia.— 

 Mix a small quantity of sulphate of ammonia with about 

 six times its bulk of basic slag in a mortar. Notice the 

 smell of ammonia. Heat a little of the mixture in an 

 ignition-tube, and hold a piece of moist turmeric-paper over 



d2 



