312 DECAY 



temperature and free unrestrained access of air. 

 The decay, on the contrary, is much retarded by 

 absence of moisture, and by the wood being sur- 

 rounded with an atmosphere of carbonic acid, which 

 prevents the access of air to the decaying matters. 



Sulphurous acid, and all antiseptic substances, 

 arrest the decay of woody fibre. It is well known 

 that corrosive sublimate is employed for the purpose 

 of protecting the timber of ships from decay ; it 

 is a substance which completely deprives vegeta- 

 ble or animal matters, the most prone to decom- 

 position, of their property of entering into fermen- 

 tation, putrefaction, or decay. 



But the decay of woody fibre is very much ac- 

 celerated by contact with alkalies or alkaline earths ; 

 for these enable substances to absorb oxygen, which 

 do not possess this power themselves ; alcohol (page 

 273), gallic acid, tannin, the vegetable colouring 

 matters (page 261), and several other substances, 

 are thus effected by them. Acids produce quite an 

 opposite effect ; they greatly retard decay. 



Heavy soils, consisting of loam, retain longest 

 the most important condition for the decay of the 

 vegetable matter contained in it, viz., water ; but 

 their impermeable nature prevents contact with 

 the air. 



In moist sandy soils, particularly such as are 

 composed of a mixture of sand and carbonate of 

 lime, decay proceeds very quickly, it being aided 

 by the presence of the slightly alkaline lime. 



