32 BULLETIN 1136, IT. S. DEPARTMENT OF AGRICULTURE. 
END COATINGS. 
When the moisture sections 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 the end grain, and if the end 
surfaces were not protected in some suitable manner the samples 
would dry out from the ends, and since they are comparatively 
short they would soon become drier than the rest of the stock and 
would not represent an average. 
A number of materials are being used to prevent or retard end 
drying under various conditions, and while some are excellent for the 
low temperatures encountered in air seasoning, comparatively few 
have proved suitable for kiln work. The most satisfactory end coat- 
ing so far tested is a 213° coal-tar pitch. There are probably other 
pitches, asphalts, and similar materials which would serve the pur- 
pose, but additional research will be required to determine the rela- 
tive efficiency of the many grades available. Materials with very 
high melting points are barred, since they can not be applied to the 
wood, and those with low melting points are unsuitable because they 
would flow off at the temperatures used in the kiln. Rosin and lamp- 
black mixtures have been used with success, but their efficiency is 
not so great as that of coal-tar pitch, and their cost is considerably 
more. No coatings, liquid at ordinary temperatures, have proved, 
so satisfactory as the hot dips. 
The ends of the moisture samples are dipped into the melted pitch 
to a depth of about one-half to three- fourths inch. The pitch should 
be hot enough to produce a smooth coating approximately one-six- 
teenth inch thick, but not hot enough to cause any of the moisture in 
the wood to flash into steam and blow holes in the coating. A very 
thin coating is undesirable on account of lack of imperviousness, and 
a thick one is wasteful of pitch and at the same time causes an error 
in the current moisture determinations. As soon as a sample has 
been dipped it should be weighed immediately and the weight re- 
corded. The average moisture content of the two moisture sections 
is assumed to be the moisture content of the sample. The oven-dry 
weight of the sample is found by multiplying the original weight of 
the sample by 100 and dividing by 100 plus the moisture content 
expressed in per cent. Thus, assume that the sample originally 
weighs 3.75 pounds and that the two moisture sections average 25 
per cent moisture. Then the oven-dry weight of the sample equals 
innj- otv i or ^ pounds. If the moisture content were expressed as 
a decimal instead of in the form of percentage, this formula would 
3.75 
be still simpler; oven-dry weight equals !j' —3. The kiln samples 
are placed in convenient parts of the various truck loads or piles of 
lumber and allowed to dry with the rest of the stock. 
Whenever a current weight is taken, the current moisture content 
is always calculated on the basis of the calculated oven-dry weight, 
just as if the sample were a regular moisture section, and the mois- 
ture content of the load is assumed to be the average of the moisture 
contents of the various samples. If the work has been accurately 
