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On the Preservation of Timber. 
The proportion of nitrogen does not exceed 1 per cent., while 
the ash varies from ^ to 5 per cent, in different kinds of wood. 
The ash consists of lime, potash, soda, oxides of iron and man- 
ganese, in combination with carbonic acid, sulphur, sulphuric 
acid, phosphorus, or phosphoric acid. Many of the bases exist 
in the sap, in combination with organic acids. The silica 
appears to exist in an uncombined state in the juices of the 
plant, and the sulphur and phosphorus must be traced to the 
albuminous constituents of the latter. 
Appeara>xe of Steuctuee of Wood. Decay of Wood. — 
The accompanying fig. 1 gives an idea of the cellular tissue, 
properly so called ; and fig. 2 the appearance presented by 
the sides of the cells incrusted with the substance above named. 
The black spaces are the canals which still remain in the cells : 
some of the former, a, are larger, and appear to be intended 
for the circulation of the sap. As the wood grows by annual 
Fi^. 2. 
Fig. 1. 
Cellular tissue. 
Sides of the cells. 
concentric layers, the central ones are older than the external 
layers, and their cells are much more incrusted with lisneous 
matter than the latter. The central layers of the tree constituting 
the heart are therefore firmer and harder than the outer layers 
forming the sa])-icood, and they are also less liable to change, as 
they contain less sap and albuminous matter, which are the 
principal agents in the decay and rotting of wood. 
Among all the substances entering into the composition of 
plants, the cellular tissue is distinguished by its great power 
of resistance against the action of chemical agents ; but a high 
temperature and the free admission of air hasten the period when 
decay commences. 
B 2 
