KILN DRYING HANDBOOK. 3 
methods b}~ which the moisture content of wood may be determined, 
but the following is the one commonly used for moisture determina- 
tions on lumber. 
Crosscut the board or stock at least 2 feet from one end, to avoid 
the effect of end drying, and then again about three-fourths inch 
from the first cut, thus securing a section as wide and thick as the 
original board and three-fourths inch long with the grain. Re- 
move all loose splinters from the section and weigh it immediately on 
a sensitive scale. Record the weight, called u original weight." 
Place the section in a drying oven kept at a temperature of about 
212° F., leaving it there until it no longer loses weight. This re- 
quires from 12 to 24 hours, sometimes longer. Leaving the sec- 
tions in the oven longer than the required time produces an ap- 
preciable error in the result. Remove the section from the oven 
and again weigh it. This will be the "oven-dry" weight, the ac- 
tual weight of the wood. The difference between the original and 
oven-dry weights is the weight of water originally in the section, 
and 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-dry weight v - r ^ n 
oven „ dry weight X100=nioisture content in per cent. 
Thus, if the green weight is 180 and the oven-dry weight 150, a 
30 
difference of 30, the moisture percentage will bey^-Xl00=20 per 
cent. The moisture content so determined is based on the oven-dry 
weight of the wood. It is, however, possible to base it upon the 
original weight. This system is occasionally used for moisture de- 
terminations by those who are accustomed to use it for other pur- 
poses. Its use is not recommended for wood sections, but it is occa- 
sionally necessary to convert moistures from one sj^stem to the other. 
The calculating and conversion formulas are given. 
Moisture content based on original _ original weight — oven -dry weight 
weight, in per cent ~ original weight X 100, 
In this system the original weight equals 100 per cent, whereas in 
the other the oven-dry weight equals 100 per cent. 
To convert moistures from one system to the other, use the follow- 
ing formula : 
. , . moisture based on original weight 
Moisture based on oven-dry weight- ^^^ based on original weight - 
BALANCES. 
Any system of weights may be used, but the metric system is more 
convenient than the others and is preferred for this reason. The 
unit of this system is the gram, and weights are expressed as grams 
and decimal fractions thereof. 
The choice of balance is a matter of personal preference and of 
first cost. For general use the balance should have a capacity of 
1 kilogram (1,000 grams) and be sensitive to 0.1 gram. These re- 
quirements are met by the ordinary analytical type of balance in 
which the two pans are suspended from an overhead beam. Other 
