﻿DECAYS AND D1SC0L0RATI0NS IN AIRPLANE WOODS. 27 



(cut up into log lengths). The practioe-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 insect 

 assist greatly in the spread of blue-stain and decay. When the I rees 

 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 slightly 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 green 

 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 treated 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 insure 

 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 (Jf, p. 17-21). 



