.524 GARDEN MANAGEMENT. 



important question how is its strength best economized. Some advocate the 

 practice of allowing the compost-heap to be entirely decomposed into an earthy 

 mass, — thus permitting the whole of the ammonia to escape ; others have gone 

 so far as not to permit of any fermentation at all, stopping all action by con- 

 tinual turning. " It must be a bad practice," says Dr. Scoffern, "to allow so 

 valuable an agent as ammonia to go to waste ; and this is the inevitable result 

 of permitting manure to undergo its last degree of fermentation. In the 

 second place, it is doubtful whether the full and immediate virtues of the 

 manure can be brought into play if it has not been submitted to incipient 

 decomposition." And he goes on to point out expedients for fixing the am- 

 monia and retaining it in all its strength, while it is reduced to a state suited 

 for assimilation as food for plants. It may be absorbed by gypsum or sulphate 



• of lime, which, being cheap, is often mixed with the compost-heap for the 

 -purpose ; the ammoniacal salts thus formed being afterwards decomposed 



by the vegetable organism, or by its agency combined with atmospheric 

 influences. 



1636. Leof-mould is a substance complex in its nature, and its functions, 

 except so far as its heating properties are concerned, are imperfectly known. 



■ The substance of any flowering plant, or leaf, being taken and comminuted by 

 rasping or cutting, and exhausted of its specific secretions by means of sol- 

 vents, all that remains behind is Hgnum and cellulose ; the components of 

 which are, carbon 24, hydrogen 16, oxygen 16. All bodies of this class yield 

 by slow decomposition results of the highest importance to the cultivation of 

 the soil ; when exposed to a sufficient amount of heat, and under the full 

 play of atmospheric air or oxygen, they burn, yielding water and carbonic 

 . acid, leaving only a trifling amount of organic matter behind. Natural decay 

 ' or eremacausis, as the chemist term it, is just such a slow combustion of moist 



organic matter as is required ; it is decomposed when freely exposed to the 



• oxygen of the air by slow burning, and the elements dissipated in gradually 

 evolved gaseous combinations.* The result is, that the gaseous fumes are 

 given off, and a blackish-looking mass remains, consisting of bodies of the 

 Jiumic acid series. When reduced to this state, they are, to all physical ap- 

 pearance, hke dark-brown soil, or earth ; and it is to their presence that 

 garden-soils owe their pecuhar colour. On ultimate analysis, these brownish 

 bodies are found to consist of humic, ulmic, and leic acids, and a substance 

 called humine ; neither of them soluble in water, but all soluble in alkalies, 

 with which they have a strong affinity. Hence their tendency to unite in the 

 •ammonia, and their value as manures in connection with alkali. " Not only 

 ■do they absorb such of this alkali as they come in contact with," says Dr. 

 Scoffern, "but it is suspected that they actually, Hke many other porous 

 -bodies, promote the combination of oxygen and hydrogen, and /o»*»i ammonia 

 by catalytic agency, — a term used by Berzelius to express the result of the 



■ contact of a third body upon two others, without being itself ol^^xred in its 



• Handy-Book of the Chemistry of Soils, p. 101. 



