KILN DRYING HANDBOOK 3 
Both species and place of growth have an important bearing upon 
the amount of moisture in living trees. Those growing in swampy 
regions are apt to contain much more moisture, and also are likely 
to be harder to dry, than similar upland species; the oaks are an 
excellent illustration of this fact. On the other hand, certain species 
contain comparatively large amounts of water even though they 
normally grow under reasonably dry conditions. All variations such, 
as these must be taken into consideration in the drafting of drying 
schedules and in actual drying operations. 
MOISTURE DETERMINATION 
To dry steck successfully, which includes knowing when it has 
reached the proper degree of dryness, the operator must be able to de- 
termine at any time the amount of moisture in the wood. Although 
there are several methods of doing this the following is the one cus- 
tomarily used for lumber. 
Crosscut the board or other stock at least 2 feet from one end, to 
avoid the effect of end drying, and then again about three-quarters of 
an inch from the first cut, thus gaining a section as wide and as thick 
as the original stock and three-quarters of an inch long, measured with 
the grain. Remove all loose splinters from the section and weigh it 
immediately on a sensitive scale. Record the weight, which is called 
“original weight.” Place the section in a drying oven kept at a tem- 
perature of about 212° F., leaving it there until it no longer loses 
weight, usually from 12 to 24 hours, although sometimes longer. 
Leaving a section in the oven for more than the required time may 
cause an appreciable error in the result. Remove the section from the 
oven and again weigh it; the scale reading will be the “oven-dry ” 
weight of the wood—the weight of the actual wood substance. The 
difference between the original weight and the oven-dry weight is the 
weight of the water originally in the section. 
In calculating the moisture percentage, first divide the difference be- 
tween the original weight and the oven-dry weight by the latter, and 
then multiply by 100. The formula is as follow: 
Moisture content in per cent, _ original weight—oven-dry weight 
based on oven-dry weight RT oven-dry weight 
« 100" @) 
Thus, if the original weight is 180 grams and the oven-dry weight is 
150, a difference of 30 grams, the moisture percentage will be 
30 grams ; 
150 grams 
is based on the oven-dry weight of the wood, a practice almost univer- 
sal. One of the important advantages of this basis is that the per- 
centages of moisture are directly proportional to their actual weights; 
if for instance a given piece of wood contains 5 per cent moisture, the 
actual weight of the moisture in it is just half of the value obtaining 
when the piece has 10 per cent moisture. 
It is possible, however, to base the moisture content of wood upon 
the original weight. ‘This system is occasionally employed for mois- 
x 100 = 20 per cent. The moisture content so determined 
