46 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
Although the kiln samples must be placed in the kiln charge at 
points where they will dry neither faster nor slower than the stock 
immediately around them, they must also be readily accessible for 
weighing. Whenever a current weight is taken, the current moisture 
content 1s always calculated on the basis of the oven-dry weight 
previously determined, just as if the sample were a regular moisture 
section, and the moisture content of the entire kiln charge is assumed 
to be the average of the moisture-content values of the various 
samples. ‘This method of estimating the moisture content of a kiln 
charge is subject to several kinds of errors, and the satisfaction de- 
rived from its use will depend largely upon the skill and the judg- 
ment of the operator. The end coating, for example, may introduce 
errors in both directions. If a heavy coating, which in itself does 
not dry out, is apphed, the current calculated moisture content will 
always be higher than the actual content because of the retention by 
the coating of weight that it would lose if it were wood. On the 
other hand, if the coating chips off, the loss in weight is credited to 
moisture loss, and the current calculated moisture content will be too 
low; replacing such a coating loss too. generously will make this 
calculated moisture content too high. If the end coating is insufii- 
ciently resistant to the passage of moisture, the samples will dry out 
faster than the full-length boards and will, therefore, indicate a 
moisture content too low for the kiln charge. Further, it has been 
found by experience, though no entirely satisfactory explanation has 
been discovered, that for green stock, particularly with softwoods, 
the kiin samples consistently show a lower moisture content, when 
dry, than the rest of the kiln charge. On account of these various 
facts it is desirable to make moisture determinations on the samples 
at the end of the run, for comparison both with the calculated values 
tor the samples and with the final moisture determinations on the 
kiln charge proper. 
In addition to the usual minor errors possible when working with 
kiln samples, however, important variations in moisture along the 
length of a sample may exist in certain species, cypress, for. instance, 
and in such species the moisture content of a sample may be quite 
different from the average content of its two moisture sections. An- 
other method may be found practical for stock of this kind, a method 
by which the dry weight of the sample is determined direct from the 
dry weight and the size of the moisture sections. The proper use 
of this method requires the sample to be of uniform cross section, and 
the moisture sections must be both cut square with it and of uniform 
length along the grain. The dry weight of the sample is then cal- 
culated as the total dry weight of the two moisture sections times 
the length of the sample, divided by the combined length of both 
sections; in other words, the dry weights of the uniform pieces are 
proportional to their lengths. Once the dry weight of the sample 
has been calculated, the rest of this method is the same as that de- 
scribed in the preceding paragraph. 
Stress sections also should be cut from the samples at the end of 
the run; in fact enough samples should be placed in the kiln so that 
current stress and moisture determinations may be made as often as 
desired. 
