316 VEGETABLE MOULD. 



minerals, with the remains of animal and vegetable 

 substances. It may be considered as earth in 

 which humus is contained in a state of decomposi- 

 tion. Its action upon the air has been fully inves- 

 tigated by Ingenhouss and De Saussure. 



When moist vegetable mould is placed in a ves- 

 sel 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 To^rooth of its own 

 weight of vegetable mould ; and the residue left on 

 its evaporation consists of common salt with traces 

 of sulphate of potash and lime, and a minute quan- 

 tity of organic matter, for it is blackened when 

 heated to redness. Boiling water extracts several 

 substances from vegetable mould, and acquires a 

 yellow or yellowish brown colour, which is dissipated 

 by absorption of oxygen from the air, a black floc- 

 culent deposit being formed. When the coloured 

 solution is evaporated, a residue is left which be- 

 comes black on being heated to redness, and after- 

 wards 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 coloured solution 

 causes no precipitate or turbidity. But dilute sul- 

 phuric acid throws down a light flocculent precipi- 



