PTTTLTPPINK WOODS. 361 
than it is wlien unseasoiiod. TIutc inay ))e several kinds of sea>iauing, 
as follows: 
1 
Natural seasoning taliny place in the tree, — This results in the formation of 
heavtsvood by the incuns already indicated. A loss of water occurs simultaneously 
with the chemical clinnfje taking plnco, and the deposit of certain substances in 
the cells more than eounterlnilances the loss in weight, so that the heartwood is 
specifically heavier, altbough lower in moisture content, than the aapwuoil. This 
change from sap- to heart-wood is very important in considering the value of a , ^ 
timber. Sapwood seems incapable of equaling Iteartwood, no matter liow care- § 
fully it may be handled after leaving the tree. 
Artificial seaswiing. — In the standing tree: In some cases, as fur instance in 
the teak forests in India, the tree is girdled and then left on the stump for a 
year or more before being cut. It is claimed that the disadvantages of tliis 
method are that the resulting wood is more brittle than if it is Reasoned in the 
usual way, and moreover, during the process it is move exposed to tlte attacks 
of burrowing insects. To ofTset this there is Uie advantage of rapiil seasoning, 
with but little checking. For some species this is probably the best method. 
In the log: Material left to season in the log usually brcomes noticeably checked. 
Rajiid seasoning is most safely accomplished in pieces of small dimensions. 
By air-drying: The greater part of our material is aii--dried — that is, scasoneil 
by standing in piles of lumber exposed to the air. If properly piled, the process 
will proceed at a fairly rapid rate and the checking will be very sliglit. The 
pile should be so arranged that tlie air can reach the wood from all sides. 
Bg l-iln-drying : This is accomplished b^' means of a controlled supply of 
artificial heat. Iviln-diying is resorted to whenever it is. desired to reduce the 
percentage of moisture below that of air-dry wood or whenever especially rapid 
seasoning is required. Tf the operation is carefully |)erformed, the wood is 
seasoned with a minimum amount of checking; it is made stronger and is less 
liable to decay. Of course, kiln-dried wood will take up moistnre from the air, hut 
it will not absorb it in as great quantity or as rapidly as the air-dried material; 
therefore, it actually remains drier than wood whicii has been seasoned in the air. 
The best results are obtained by prolonged and carefnl air-drving. followed by kiln- 
drying. If properly handled, wood is always improved by l>eing kiln-ilried. 
X'nfortnnately^ the process is not as much practiced with the native woods as it 
should be. 
Reasoning in fluids: Timbers sometimes are submerged in sea water for years 
before being dried, additional strength and durability apparently being given to 
them. For many years this has been the process with oak nsed for sliipbuilding 
in England. Of course this method of seasoidng can <»nly l« employed where 
the material can be so submerged as to be free from teredo attack. Timbers 
occasionally are encountered which have had a part of their seasoning in fresh 
water or in the mud at the bottom of fresh-water streams or lakes, an example 
being the swamp cypress logs which are raised fiitm the mud of rivers and hayons 
in the southern ITnited States, after having lain there for many years. 
Small pieces of woods for certain purpobcs arc seasoned in (til or other fluids. 
All these methods of submerging woods during seasoning have the very great 
advantage that the process is thereby made a very gradual and imiform one, 
checking being reduced to a minimum. However, these methods are suited only 
to special cases. 
Heating potrcr. — This varies with the content of carbon and contained 
resins, oils, etc. Our l)est firewoods are usually those with very thick, 
dense cell-walls. 
