196 ANNUAL EEPOKTS OF DEPARTMENT OF AGEICULTUEE. 



scientific basis for the use of wood. Over 500 tests were made from 

 Sitka spruce, white oak, and yellow birch to determine the influence 

 of drying and steaming on strength, with particular reference to use 

 in airplanes. Tests upon beams to determine the effect of continuous 

 loading were continued. 



Kiln-drying tests previous to the entrance of the United States into 

 the war continued along the same lines as in the past. Encouraging 

 tests on structural sizes of Douglas fir show the possibility of kiln 

 drying without appreciable loss of strength. A method was per- 

 fected under which hemlock ship-lap can be dried to shipping condi- 

 tion with practically no degrade in 40 to 48 hours, and 2-inch plank 

 in from 4 to 6 days. Douglas fir and red and white fir were also 

 dried to practically a perfect condition in 48 hours. The 'time for 

 drying maple last blocks was reduced from 21 to 2 months, and losses 

 reduced from an average of about 15 per cent to 6 per cent. Green 

 basswood was satisfactorily dried in 2-inch thicknesses in 13 days 

 and 1-inch thicknesses in 9 days. Dogwood sticks and ironwood 

 blocks were dried in comparatively short periods without checking or 

 honey-combing. Work was largely completed on spruce and ash for 

 airplanes, the problem being to dry the material in the minimum 

 time without loss of strength and toughness as compared with air- 

 dried stock. 



In the wood-preservative work the most striking development of 

 the year was the initiation of tests to detennine the best preservative 

 treatment for construction wood in cotton mills, where conditions are 

 extremely favorable to decay. With -particular reference to the 

 textile-mill region of the East, practical aspects of timber-decay 

 problems in buildings were studied in cooperation with the Bureau 

 of Plant Industry. Tests were continued, with some success, to devise 

 methods for the satisfactory impregnation of Douglas fir with wood 

 preservatives. White birch, in a test wood pavement in Minneapolis, 

 made a remarkable showing for 10 years and proved fully equal to 

 longleaf pine. A report prepared for publication points out correct 

 methods of construction for wood paving and thus makes it possible 

 to avoid the difficulties which have been experienced in the past. A 

 report was completed covering the results of 10 years' tests of approx- 

 imately 12 wood preservatives on ties of 61 species laid in test tracks 

 in 33 railroads. Continuing investigations on treated silo timber 

 corroborate preliminary tests that creosote does not appreciably 

 injure silage. Cooperation with the Bureau of Fisheries brought 

 out the relationship between the boiling point and toxicity of pre- 

 servatives against marine borers, and should prove of value in the 

 development of a special marine creosote for use in heavily infested 

 water. Additional experiments were begim to find a preventive of 

 sap stain in timber, deterioration from which causes a loss amounting 

 to several millions of dollars annually. In cooperation with the 

 Bureau of Plant Industry, the direct relation between toxicity and 

 volatility of coal-tar creosotes was established, so that it is now pos- 

 sible to determine toxicity from distillation curves, as in the case 

 of mixtures of coal-tar creosote and gas oils and of creosotes and 

 crude oils. With especial reference to airplanes, the efficiency of 

 glues and the best technique for their use was studied, and work on 

 treatments and coatings to reduce or prevent the absorption of mois- 

 ture and consequent shrinkage and expansion continued. 



