28 CALIFORNIA TANBARK OAK. 



Data are not available for a comparison of the toughness and stiff- 

 ness of tanbark oak and the eastern oaks and hickories. 



Table 11 shows a considerable increase in the strength values of 

 the air-dry material over the green, and a still further increase in 

 these values for the kiln-dry material. 



In compression perpendicular to the grain, green tanbark oak has 

 an average strength at the elastic limit of 1,355 pounds per square 

 inch. Green Douglas fir has an average strength of 651 pounds per 

 square inch. 



In shearing strength air-dry tanbark oak shows an average of 

 1,960 pounds per square inch. Douglas fir has an average shearing 

 strength of 770 pounds per square inch for air-dry pieces. 



Douglas fir would, of course, be expected to have lower strength 

 values than a hardwood like tanbark oak. The comparison is used 

 because such tests on other hardwoods have not yet been made. 



SEASONING. 



A number of the logs selected for testing purposes were sawed into 

 boards for a seasoning test. Fifty 1-inch boards were put through a 

 commercial dry kiln of the moist-air type in San Francisco. The 

 results, while encouraging as regards the behavior of tanbark-oak 

 lumber in a moist-air kiln, were not satisfactory, owing to the imperfect 

 regulation of the kiln and consequent daily variations in temperature 

 and humidity. After 40 days in the kiln a classification of the lumber 

 gave the following: 



The average temperature of the kiln was only 85 F. for the 40 

 days, whereas it should have been at least 110 F. The loss in sea- 

 soning eastern oak for vehicle stock is placed at about 10 per cent. 



The method of seasoning used by a lumber company which owns 

 considerable tanbark-oak stumpage that it is preparing to put on the 

 market in the form of flooring is as follows : The logs as soon as con- 

 venient after they come in from the woods are cut into IJ-inch 

 material. This is then carefully piled in the open yard, with sticks 

 every 18 inches, and allowed to dry from 3 to 6 months. It is finally 

 kiln dried from 30 to 40 days at a temperature not to exceed 110 

 F., when the boards are ready to be made into flooring. The kiln used 

 is of the blower type. The results obtained in drying tanbark oak by 

 this method have been very satisfactory. It should be remembered 

 that the trees in this case were cut during the peeling season (May to 



