﻿KILN DRYING HANDBOOK. 3 



nethods by which the moisture content of wood may be determined, 

 >ut the following is the one commonly used for moisture determina- 

 ions on lumber. 



Crosscut the board or stock at least 2 feet from one end, to avoid 

 he effect of end drying, and then again about three-fourths inch 

 rom the first cut, thus securing a section as wide and thick as the 

 original board and three-fourths inch long with the grain. Re- 

 aove all loose splinters from the section and weigh, it immediately on 

 1 sensitive scale. Record the weight, called " original weight." 

 5 lace the section in a drying oven kept at a temperature of about 

 12° F., leaving it there until it no longer loses weight. This re- 

 hires from 12 to 24 hours, sometimes longer. Leaving the sec- 

 ions in the oven longer than the required time produces an ap- 

 preciable error in the result. Remove the section from the oven 

 nd again weigh it. This will be the "oven-dry" weight, the ac- 

 ual weight of the wood. The difference between the original and 

 ven-dry weights is the weight of water originally in the section, 

 ,nd the moisture percentage is readily calculated. 



Divide the difference between the two weights by the oven-dry 

 weight, and to reduce to per cent multiply by 100. The formula is : 



Original weight — oven-drv weight 



„ ~ ,„ r-r- — — X100=moisture content in per cent. 



oven-dry weight ^ 



Thus, if the green weight is 180 and the oven-dry weight 150, a 



30 

 lifference of 30, the moisture percentage will be t^ttX 100=20 per 



;ent. The moisture content so determined is based on the oven-dry 

 veight of the wood. It is, however, possible to base it upon the 

 jriginal weight. This system is occasionally used for moisture de- 

 erminations by those who are accustomed to use it for other pur- 

 >oses. Its use is not recommended for wood sections, but it is occa- 

 ionally necessary to convert moistures from one system to the other, 

 rhe calculating and conversion formulas are given. 



[oisture content based on original _ original weight — oven-dry weight 



weight, in per cent original weight X ° 0- 



In this system the original weight equals 100 per cent, whereas in 

 he other the oven-dry weight equals 100 per cent. 



To convert moistures from one system to the other, use the follow- 

 ng formula : 



. , moisture based on original weight 



Moisture based on oven-dry weighty— ^-g based on original weight » 



BALANCES. 



Any system of weights may be used, but the metric system is more 

 icnvenient than the others and is preferred for this reason. The 

 mit of this system is the gram, and weights are expressed as grams 

 nd decimal fractions thereof. 



The choice of balance is a matter of personal preference and of 

 irst cost. For general use the balance should have a capacity of 

 . kilogram (1,000 grams) and be sensitive to 0.1 gram. These re- 

 tirements are met by the ordinary analytical type of balance in 

 vhich the two pans are suspended from an overhead beam. Other 



