4i8 



THE TIMBERS OF THE WORLD 



to find out the exact percentage of moisture in seasoned wood, and then 

 use moisture tests to see that the timber is dried to a corresponding 

 percentage. 



A very simple apparatus has been designed by Lieutenant Kennedy 

 of the Aeronautical Inspection Directorate, for determining the moisture 

 content in wood. It consists of an hydrometer balance for weighing, 

 and a gas-heated oven for drying out the sample. The hydrometer is 

 graduated to take a convenient quantity of wood chips which contain 

 an unknown amount of moisture, when sunk to the zero mark. After 

 baking out the moisture from the sample, and consequently reducing its 

 weight, the scale shows directly the percentage of moisture which these 

 wood chip samples contained. 



It is a great mistake to dry out the timber completely. If wood is 

 " bone dry " it is as dead as a bone. Timber thoroughly seasoned by 

 natural means contains anything between g per cent to 15 per cent of 

 moisture, and as this may be regarded as being the standard of excellence, 

 it forms a guide for artificial seasoning. It is easier, as far as working 

 is concerned, to dry out completely, and then allow the material to 

 reabsorb moisture from the atmosphere, but this should be avoided in 

 all cases where brittleness would be a disadvantage. 



Degrees of dryness should vary according to the use to which the 

 timber will be put. For inside work, such as joinery, furniture, and wood- 

 block flooring, where thorough dryness is necessary, 8 per cent to 10 per 

 cent moisture should be allowed, though for export to the tropics the 

 amount should be no more than 6 per cent. For outside work, such as 

 coach-building, 10 per cent to 15 per cent would be the normal amount, 

 and for special cases, such as shafts, stretcher poles or aeroplane langerons, 

 where flexibility is all-important, and a little shrinkage is immaterial, an 

 even greater amount of moisture should be left in the timber. In general, 

 where the ultimate purpose for which the timber will be used is unknown, 

 the seasoning process should be operated so as to retain between 12 per 

 cent to 15 per cent in the seasoned wood. 



