VEGETABLE MOULD. 345 



having been washed with water, is brought whilst still moist 

 under a receiver filled with oxygen, the gas is absorbed with 

 great rapidity ; and the same thing takes place when the pre- 

 cipitate is dried in the air. In the perfectly dry state it has en- 

 tirely lost its solubility in water, and even alkalies dissolve only 

 traces of it. 



It is evident, therefore, that boiling water extracts a matter 

 from vegetable mould, which owes its solubility to the presence 

 of the alkaline salts contained in the remains of plants. This 

 snbstance is a product of the incomplete decay of woody fibre, 

 and contains a certain quantity of ammonia chemically combined. 

 Its composition is intermediate between woody fibre and humus, 

 into which it is converted, by being exposed in a moist condition 

 .o the action of the air. 





