44 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
forest products laboratory prefers the latter basis, using it wherever 
possible. ' 
The nature and use of the schedules are discussed later, beginning 
on page 47. 
KILN SAMPLES 
The successful employment of a drying schedule based upon the 
current moisture content of the kiln charge requires a system by 
which this content can be determined with both ease and certainty. 
The best system so far developed depends upon the use of kiln 
samples. These samples are short pieces of typical stock of known 
original moisture content which, placed in representative parts of the 
kiln, are allowed to dry with the rest of the charge and are peri- 
odically weighed to determine the loss in moisture of each of them. 
Their current moisture-content values are then computed from the 
original moisture-content values and the losses in weight, and the 
average of the current values is assumed to be the average moisture 
content of the entire kiln charge. , 
Kiln samples are prepared as follows: Several pieces, representing 
both fast-drying and slow-drying stock, but usually not sapwood, 
are selected from the stock to be dried, and from each of them one 
or more samples fully 2 feet long are cut. In order to avoid the un- 
certainty in the condition of the ends usual with lumber, the samples 
should, if possible, be cut not less than 2 feet from the end of the 
piece. A moisture section should immediately be taken from each 
end of each sample, and the moisture determinations should be care- 
fully made. The average of the results from each pair of sections 
is assumed to be the average moisture content of the corresponding 
sample. 
END COATINGS 
When the moisture sections cut from the kiln samples have been 
weighed and placed in the oven the samples should be end coated. 
It has already been shown that wood dries out much faster from end 
grain than from side grain, and if their end surfaces were not pro- 
tected in some suitable manner the comparatively short samples 
would soon become drier than the rest of the stock and would then 
fail to represent average conditions in the kiln charge. 
The end coatings commonly used are of two classes, those liquid 
at ordinary temperatures, which can be applied cold, and those solid 
at the same temperatures, which must be applied hot. Either the 
cold or the hot coatings can be used effectively for drying temper- 
atures up to 140° F. Temperatures much above this cause blistering 
in the cold coatings, but make the hot type plastic enough to form a 
new surface as fast as the old one breaks. For this reason the hot 
coatings are likely to be more effective than the cold for tempera- 
tures from 140° up to 170° F., where they liquefy to such an extent 
that they run off. No coating has been found that is entirely satis- 
factory for temperatures above 170° F. Cold coatings are perhaps 
somewhat better than hot for all uses in temperatures above 170° 
F., and in addition for any kiln samples that may be placed in tem- 
peratures below this value but still high enough to cause the loss of 
part of a hot coating, with the resultant error-making change in the 
weight of the sample. Some asphalts are strongly moisture-resist- 
