DURABILITY OF WOOD. 233 



that is to go at once into the water these precautions are 

 not so important. 



Heat (60 Degrees to loo Degrees Fahr.), Moisture 



and Air in moderate quantities produce conditions under 

 which wood quickly decays. It is on this account that 

 fence posts rot off near the surface of the ground, where 

 about such conditions of heat and moisture are usually 

 found during several months of the j^ear. For the same 

 reason what is known as dry rot destroys green floor 

 joists or other timbers where they are tightly enclosed, 

 as under a house without ventilation, since moisture is 

 always present in such places, and the timber cannot dry 

 out. Perfectly dry wood or that submerged in water will 

 last indefinitely, and there seems to be no difference in 

 different kinds of wood under these conditions. Pieces 

 of pine wood in good condition have been found in Illi- 

 nois, buried to a depth of sixty feet, that must have been 

 there for many centuries. Nearly sound pine logs are 

 occasionally found in the woods of this State, where they 

 have a thick moss covering that has kept them moist and 

 prevented their decay for hundreds of years. The remains 

 of timbers in the piles of the lake dwellers in Switzer- 

 land, which must have stood in place two thousand years, 

 are still intact. In these instances the wood was kept 

 moist, and never came in contact with the air. It is very 

 evident, too, that wood which is kept in a dry place does 

 not decay, since it may be found in an unimpaired state 

 of preservation in some of our very oldest buildings. 



In the following table is shown approximately the time 

 fence posts will last in Minnesota. This table is based on 

 practical experience in that State: 



