The composition of wood is shown in the following table : -

Carbon.

Hydrogen.

Oxygen.

Nitrogen.

Ash.

per cent.

per cent.

per cent.

per cent.

per cent.

Beech ...........

49.36

6.01

42.69

0.91

1.00

Oak........

49.64

5.92

41.16

1.29

1.97

Brich........

50.20

6.20

41.62

1.15

0.81

Poplar..........

49.37

6.21

41.60

0.96

1.86

Willow......

49.96

5.96

39.56

0.96

3.37

Average.........

49.70

6.06

41.30

1.05

1.80

Practically.........

50

6

41

1

2

Wood, in its raw state, contains a large amount of water, which holds more or less soluble minerals, and is called sap. By drying wood a great part, but not all, of this water is evaporated. If wood is dried in a closed vessel, and then exposed to the atmosphere, it quickly absorbs moisture; but the moisture thus absorbed is much less than the wood originally contained. The amount of water varies in different kinds of wood, and according to the season. Wood cut in April contains 10-20 per cent. more water than that cut in January. The following table shows the percentage of water in woods, dried as far as possible in the air : -

Beech ........ 18.6

Poplar ........ 26.0

Sugar and common maple 27.0

Ash.......... 28.0

Birch.......... 30.0

Oak, red........ 34.7

Oak, white ...... 35.5

Pine, white ...... 37.0

Chestnut . ...... 38.2

Pine, red........ 39.7

Pine, white ...... 45.5

Linden ........ 47.1

Poplar, Italian .. .. 48.2

Poplar, black...... 51.8

Wood cut during December and January is not only more solid, but will dry faster than at any other period of the year, because the sap by that time has incorporated a great part of soluble matter with the woody fibre; what remains is merely water. When the sap, during February, March, and April, rises, it partly dissolves the woody fibre, and the drying of the wood is not only retarded, but the wood is weakened in consequence of the matter thus held in solution.