40 The l^'oKEST Pkoducts IvAjjokatoky 



rate, and on armistice day the entire force niiinl)ered 4.58 persons. 

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

 emergency work dropped. However, certain of the ])rojects, espe- 

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

 continued, support for them being largely fm-nished by the cooperat- 

 ing bureaus. The war expansion and the relative personnel situation 

 today and in 1917, prior to the sudden growth of tlie laboratory, can 

 be seen at a glance in tlie diagram on page -'50. 



Kiln Drying of Aircraft Woods 



In presenting the accomplishments of tlie 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 researcli. The demands of the 

 allied nations for aircraft materials in the years ])rece(ling 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 Mas entirely inadequate: though even had it 

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

 hibitive. The only alternative was kiln drying.l'tilizing 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 ecjual to or better than air-dried stock. 

 The preparation of kiln-drying specifications covering the principal 

 aircraft w^oods followed and they were almost immediately approved 

 by the Signal Corps and l)ecame the standard for both Army and 

 Xavy. 



T/nder these specifications it was possible to dry three-inch green 

 s])riice planks in 21 days, ordinary air seasoning taking from six 

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

 suitable kilns m ere erected by the Army and Xavy for the drying of 

 aircraft woods, the largest of tliese 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 



