DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 21 
(cut up into log lengths). The practice of leaving logs lying in the 
woods for months can not be too strongly condemned, as this not only 
causes blue-stain but also promotes the growth of wood-destroying 
fungi. Furthermore, the inevitable attacks of wood-boring insects 
assist greatly in the spread of blue-stain and decay. When the trees 
are bucked the narrow space left by the saw kerf between the logs as 
they are lying end to end affords an ideal situation for the develop- 
ment of the blue-stain fungi. Such logs often stain deeply, while 
those with the ends fully exposed remain ‘entirely free from discolora- 
tion. As soon as the logs are in the mill pond danger from staining 
is over for the time being, since the oxygen supply is so reduced that 
the fungi can not develop. 
The greatest danger of all is encountered during the process of 
drying the rough lumber as it comes from the saw. The best method 
of preventing blue-stain is by kiln drying. If the stock checks easily, 
so that low ‘temperature and high humidities must be maintained 
over a considerable period, some of the other staining fungi such 
as molds, may develop. But these can be checked by raising the tem- 
perature in the kiln to about 160° F. or shghtly more for an hour 
by turning live steam into the kiln. When this is done, care must be 
taken to keep the air saturated while steaming and to reduce the 
humidity gradually after steaming. When the “stock has once been 
dried properly the moisture content has been so reduced that there 
is no more danger from staining, provided it is kept dry. A dispute 
that arose over the efficiency of a dry kiln was immediately settled 
by the fact that the blue-stain fungi had resumed vigorous growth 
the day after the stock was removed from the kiln. This could not 
have occurred if the lumber had been properly dried. 
All airplane lumber should be kiln-dried immediately, since this 
not only prevents blue-stain, but also stops the growth of wood-de- 
stroying fungi, prevents future checking, and greatly reduces weight 
without in any way injuring the lumber, provided temperatures that 
are too high are avoided. 
In case ‘kiln drying is impossible, treatment with antiseptic solu- 
tions is of considerable value. As it comes from the saws the ereen 
lumber is dipped into a hot or cold chemical solution. The solutions 
most commonly employed are sodium carbonate or sodium bicar- 
bonate in water. Neither is 100 per cent effective under optimum 
conditions for staining, but they aid materially in checking discolora- 
tion. These two chemicals, however, color the tr eated wood a 
decided yellow or brownish. Sodium fluorid, although it does not 
stain the lumber and is slightly better for blue-stain, is not so effec- 
tive against certain molds as the two solutions first mentioned. ‘This 
chemical is seldom used. It must be remembered that the strength 
of the solutions must necessarily vary with the conditions. The more 
favorable the conditions for blue-stain, the stronger the solutions 
should be. 
After being dipped in any of these solutions the lumber must be 
carefully open piled, that is, with spaces between the boards to imsure 
good ventilation. Narrow cross strips or “stickers” chemically 
treated should be used, to prevent staining at the points where the 
boards and cross strips meet. Detailed instructions as to the proper 
methods of piling lumber may be consulted elsewhere (4, p. 17-21). 
