CHEMISTRY OF THE FARM- YARD. 101 



to follow the changes which the fibre undergoes, 

 after having left the stable, and being cast upon 

 the dung-heap.* The decomposition goes on 

 at so rapid a rate, that the temperature of the 

 mass rises very considerably ; and we know 

 familiarly, that the heat thus produced, is 

 turned to good account by horticulturists, for 

 the formation of their hot-beds. As a tolerably 

 equable source of moist heat, it is almost un- 

 equalled for such purposes. The long and 

 glittering stems of the straw break up, lose their 

 golden lustre, and are gradually reduced to an 

 earthy, brown mass. The change is now com- 

 plete, and in the crumbling condition in which 

 it is now found, it is transferred again to the 

 fields, the scenes of its bygone youth, vigour, and 

 ripe age. 



Thus is vegetable mould, strictly so called, 

 chemically produced. It must, therefore, be 

 regarded as a layer of material, in which, as we 

 have said, continual processes of decomposition 

 are going forward. A large amount of oxygen 

 is absorbed from the air, and a continual return 

 is made by the disengagement of carbonic acid 

 gas. Vegetable mould in this condition is, we 



* In consequence of the volatile nature of the carbonate 

 of ammonia, formed in the decay of manure, this proceeding 

 is a very wasteful one, since this substance is found to con- 

 stitute a great part of the efficacy of such manure. 



