40 The Foeest Products Laboratory 



rate, and on armistice day the entire force numbered 458 persons. 

 After that time, the personnel was gradually reduced, and much of the 

 emergency work dropped. However, certain of the projects, espe- 

 cially those of importance in peace-time developments, have been 

 continued, support for them being largely furnished by the cooperat- 

 ing bureaus. The war expansion and the relative personnel situation 

 today and in 1917, prior to the sudden groA\i:h of the laboratory, can 

 be seen at a glance in the diagram on page 39. 



Kiln Drying of Aircraft Woods 



In presenting the accomplishments of the laboratory during the 

 war period, it will be necessary to include a certain amount of back- 

 ground, so that each research may be properly oriented and fitted into 

 the general plan of national defense. The very essence of this work 

 was the necessity for the development of unprecedented supplies of 

 spruce for aircraft production and research. The demands of the 

 allied nations for aircraft materials in the years preceding the entry 

 of the United States into the war had practically cleaned up the avail- 

 able supply of air-dry spruce in the country and in addition, the pro- 

 duction of green spruce was entirely inadequate; though even had it 

 been sufficient, the delay incident to air drying would have been pro- 

 hibitive. The only alternative was kiln drying. Utilizing the available 

 knowledge possessed by the laboratory in this field, the proper authori- 

 ties were convinced of the practicability of kiln drying material green 

 from the saw to a condition equal to or better than air-dried stock. 

 The preparation of kiln-drying specifications covering the principal 

 aircraft woods followed and they were almost immediately approved 

 by the Signal Corps and became the standard for both Army and 

 Navy. 



Under these specifications it was possible to dry three-inch green 

 spruce planks in 21 days, ordinary air seasoning taking from six 

 months to a year, depending upon climatic conditions. Batteries of 

 suitable kilns were erected by the Army and Xavy for the drying of 

 aircraft woods, the largest of these being at Vancouver Barracks, 

 Washington. In the erection and operation of this large drying plant 

 considerable technical advice and assistance was rendered by the lab- 

 oratorv. Several aircraft manufacturers also installed similar kilns 



