38 PRACTICAL AGRICULTURAL CHEMISTRY [99-101 



a small quantity of dilute hydrochloric acid. The liquid 

 will effervesce, owing to the fact that bones contain carbonate 

 of lime. 



COMPOUND MANURES' 



* 99. The following set of experiments (paragraphs 100- 

 106) should be performed on several mixed manures. The 

 object of the experiments is to find out what are the principal 

 constituents of the manures. 



* 100. Test for Acidity.— Place a little of the mixed 

 manure on a watch-glass, moisten it thoroughly with water, 

 and lay a piece of moist blue litmus-paper upon it. Should 

 the litmus-paper immediately become red, the manure con- 

 tains some acid, and most probably contains superphosphate 

 of lime. 



* 101. Test for Soluble Phosphate.— Place about 

 as much of the manure as could be held on a penny in a 

 mortar, cover with cold distilled water, and grind into a paste 

 with the pestle. Allow the liquid to settle for two or three 

 minutes, then filter it, washing the mud into the filter-paper 

 with hot water. Save the residue for the next experiment 

 Divide the filtrate into two portions in test-tubes. Test one 

 portion for phosphoric acid by boiling with excess of ammo- 

 nium molybdate solution. 



Should a yellow precipitate occur, then the manure con- 

 tains soluble phosphoric acid, and should the manure have 

 been proved by the last experiment to be acid then we may 

 consider that it contains either superphosphate or dissolved 

 bones. 



To the second portion of the filtrate add ammonia ; a 

 white precipitate of phosphate will be formed. Allow this 

 to settle and notice the colour of the liquid. If it be quite 

 colourless, then the soluble phosphate was mineral super- 



1 Two or three mixtures of the more important manures should be 

 provided and the student allowed to discover their constituents. 



