274 TIMBER 



Even the amount of moisture in so called " dry wood " is 

 not always the same. The late Professor J. B. Johnson, in 

 his "Materials of Construction," says "the weight of a 

 pailful of shavings varies with the time of day, being on a 

 summer day greatest in the morning and least in the after- 

 noon. Wood kept on a shelf in an ordinary dwelling-house 

 retains 8 to 10 per cent, of its weight of water, and this 

 percentage is always greater than the percentage of the 

 surrounding air." 



The timbers of the temperate zone contain least sap if 

 cut at the fall of the year and thus season more readily, 

 but the time of felling does not affect their strength or 

 durability. 



Artificial Seasoning. Kiln drying, where the timber is 

 stacked in a tank and exposed to temperatures of hot air 

 from 150 to 180 Fahr., is a quick, useful, and satisfactory 

 method of seasoning timber when it is required urgently. 

 Some soft woods are put into the tank fresh from the saw ; 

 hard woods are allowed to season in the air for some months 

 previously so as to allow shrinkage to take place more 

 gradually, as they are more liable to split by sudden drying. 

 As a rule lower temperatures of 100 to 120 Fahr. are 

 employed when the timber is kiln dried in a green state, and 

 sometimes dry steam is applied to it during the process to 

 enable the seasoning to take place more gradually and with 

 less risk. In the above temperatures pines, spruce, cedar, 

 and soft woods are generally allowed about four days for 

 1-inch boards, and hard woods, after being air dried for three 

 to six months to allow the first shrinkage to take place, are 

 placed in the kiln for from six to ten days for the same 

 thickness of boards. 



Careful stacking of the timber, so as to allow spaces 

 around each piece, is as necessary in kiln drying as in 



