344 VEGETABLE MOULD. 



CHAPTER XII. 



Vegetable M m\d. 



The term vegetable mould, in its general signification, is 

 applied to a mixture of disintegrated minerals, with the remains 

 of animal and vegetable substances. It may be considered as 

 earth in which humus is contained in a state of decomposition. 

 Its action upon the air has been fully investigated by Ingenhouss 

 and De Saussure. 



When moist vegetable mould is placed in a vessel full of air, it 

 extracts the oxygen therefrom with greater rapidity than decayed 

 wood, and replaces it by an equal volume of carbonic acid. 

 "When this carbonic acid is removed, and fresh air admitted, the 

 same action is repeated. 



Cold water dissolves only -f oooo " tn °f * ts own weight of vege- 

 table mould; the solution is clear and colorless, and the residue 

 left on its evaporation consists of common salt with traces of sul- 

 phate of potash and lime and a minute quantity of organic mat- 

 ter, for it is slightly blackened when heated to redness. Boiling 

 water extracts several substances from vegetable mould, and 

 acquires a yellow or yellowish brown color, which is dissipated 

 by absorption of oxygen from the air, a black flocculent deposit 

 being formed. When the colored solution is evaporated, a 

 residue is left which becomes black on being heated to redness, 

 and afterwards yields carbonate of potash when treated with 

 water. 



A solution of caustic potash becomes black when placed in 

 contact with vegetable mould, and the addition of acetic acid to 

 the colored solution causes no precipitate or turbidity. But 

 dilute sulphuric acid throws down a light flocculent precipitate 

 of a brown or black color, from which the acid can be removed 

 "with difficulty by means of water. When this precipitate, after 



