206 AlsTNUAL REPORTS OF DEPARTMENT OF AGRIC'JLTURE. 



as air-dried riimber. They show further that the kihi-drying 

 schedules recommended by the laboratory at the beginning of the 

 war and based upon the incomplete* data then available were in 

 every sense dependable and are subject to practically no material 

 changes. Up to the date of the armistice, assistance had been given 

 in the design, installation, and operation of 325 Forest Service 

 water spray kilns installed in 44 manufacturing plants throughout 

 the country, including installations at the Government cut-up 

 plant of the Spruce Production Division, and at the Rock Island 

 Arsenal. At the latter plant a laboratory representative demon- 

 strated that artillery wheel dimension oak, green from the saw, can 

 be kiln-dried with insignificant loss in from 60 to 90 days as against 

 3 to 5 yeai-s of air seasoning. This was contrary to previous com- 

 mercial experience. Other kilns were designed for use at Govern- 

 ment arsenals, aircraft factories, gun manufacturing plants, and 

 vehicle plants. The Signal Corps dry kilns at Vancouver, Wash., 

 were started in June, 1918, under the personal supervision of a kiln 

 expert from this laboratory. The first kihi load of airplane wing 

 beams was taken out on July 16. Thereafter the kilns were con- 

 tinuously operated at full capacity of about 40,000 feet per day 

 until the end of the war. A corps of kiln experts was maintained m 

 the field to assist vehicle, furniture, and aircraft manufacturers in 

 the adaptation and operation of commercial kilns used in war work, 

 and intensive courses of training for Government and commercial 

 dry-kiln operators and inspectors were continued until the armistice 

 was signed. 



The total number of laboratory strength tests was brought up to 

 over 300,000. About 23,000 strength tests were completed on 32 

 species of plywood, to determine the strength variation with differ- 

 ent combinations of species, number of plies, and ratios of core to 

 total panel thickness. Many additional tests were made to deter- 

 mine the relative amount of warping of various species of plywood, 

 the bending strength and methods of fastening, the relative strength 

 of rotary, sliced, and sawed veneer, and the shearing strength and 

 shrinkage of pl3rwood. Other tests were made on various aircraft 

 parts of plywood, laminated, and fabricated material, such as engine 

 bearers, struts, landing-gear disks, wing ribs, elevator spars, etc. 

 Determmations were made of the mechanical properties of thin ply- 

 wood for use as a Hnen substitute, and the relative efficiency of 

 various types of riveted and scarf joints was investigated. 



Tests conducted for the War Lfepartment made possible great 

 improvements in overseas shipping containers, and many inspectors 

 were trained in the fundamentals of box construction, for manu- 

 facturing and export inspection work. Wood preservative specifica- 

 tions were j^repared for the Emergency Fleet Corporation and for 

 the Railroad Administration. To assist the latter in its program of 

 preservative distribution made necessary by the shortage of creosote, 

 substitute preservatives were tested and recommendations as to their 

 use were made. 



Studies were completed of the effectiveness of various methods of 

 coating and finishing wood to prevent the j^assage of moisture. 

 Improved methods of finishing with varnishes were developed, and 

 it was shown that protective coating with thin sheets of aluminum 

 leaf is practically 100 per cent efficient. In an experimental shipment 

 of airplane propellers from this country to France those treated by 



