Compiled by: Prajna Khanal, Smriti Pahari and Siddhartha Aryal Page | 32
happy features all the time as it interfere industrial utilization e.g. Thuja plicata, Shorea guiso
Extraneous substances can be organic or inorganic
1. Inorganic extractives:
They are either purely inorganic salts, including free silica, or salts of organic acids, and those from
ash on burning.
Ash content and the composition vary with place, growing condition and the season of the year.
The metallic radicles are principally calcium, potassium, and magnesium. Aluminium, iron, manganese
and sodium are also sometime met with.
In some cases some metals are in high quantity as in the ashes of Abies pectinata contains
40% potash, 28% manganese),
There are cases where barium, titanium, lead, zinc, copper cobalt, nickle,, silver and even gold
have been detected in very small amount. Acid radicals like carbonate, sulphate, silicates,
phophates and chlorides also occurs in several cases.
B. Organic extractives :
1. Essential oils - present usually below 1% but in some species more (up to 12% in Araucaria species,
8% in Indian sandal wood ), usually obtained from heartwood by distillation or solvent extraction.
Essential oil is a mixture of various types of compounds: hydrocarbons, acids, phenols, alcohols,
oxides, ether, ketones, lactones
2. Wood resins -found in resin channels but also in cell walls and the interior of the cells, composed
of resin acid and fatty acid. Can be obtained from sapwood of living trees, heartwood, from felled
trees as tall oil (soda and sulphate pulping process).
3. Dyes and tans -barks, roots, leaves, flowers, wood, and other parts of plants contains many tanning
and colouring matters. E.g. khair, Mahogany, etc. for colour; tannin - eg.tannins from oak in tanning
animal hides into leather; use for producing anticorrosive primer)
4. Carbohydrate components -0.5 to 5%, in starch, polysaccharides, simple sugar form. Disadvantage
is that large amount of starch in the wood are more susceptible insect acttack.
5. Cyclitols -sweet like sugar, but neither contain any carbonyl group nor do they ferment.
6. Other extraneous materials-fatty oils (in Tilia spp.), alkaloids (in leguminosea, Rubiaceae)
Mechanical properties of wood
It is the ability of wood to resist various types of external forces, static or dynamic, that may
act on it.
Stress- It is the force acting on a unit area strain- It is the deformation per unit measure (of
length, area, volume)