A Decennial Kecoud 47 



iitely undertaken. A special staff of chemists and assistants was 

 gathered together, and the necessary ecjuipnient installed. Tliis ^ irtii- 

 ally marks the lahoratory's entrance into glue research. 



Within a reasonahle time, higli class glues of })oth types. ])loo(l 

 albumin and casein, had been worked out and made available to the 

 Bureau of Aircraft Production, llegular inspection and test of sam- 

 ples of plywood glued at various plants had })een established early in 

 the study and was maintained as an aid to tlie manufacturers in mak- 

 ing a satisfactory product. Assistance was rendered them, also, by 

 trips of inspection and study at the individual plants. In addition to 

 the glues already mentioned, a special kind of blood albumin glue 

 tissue was invented. This is particularly adapted to the gluing of very 

 thin plywood, such as that used in the experiments on plywood wing 

 covering. In connection with the glue work, special studies of the 

 supplies and (juality of the raw materials entering into their manufac- 

 ture were undertaken. Through these, adequate quantities of suitable 

 material became assured. 



Propeller Work 



The effect of moistm-e upon the properties of wood was well 

 known, and it was generally accepted tliat the planes and their parts 

 should be manufactured at the moisture content which they would 

 assume in service. There were already in existence certain data sliow- 

 ing the relation between atmospheric humidity and the moisture in 

 wood, but these were not considered sufficient in view of the import- 

 ance of the matter. Therefore, several series of accelerated tests were 

 made, the results permitting the determining in advance of moisture 

 content tliat will be reached by any species under given atmospheric 

 conditions. 



Closely correlated with this study was an entirely dissimilar one, 

 planned to prevent change in the moisture content of propellers espe- 

 cially dm-ing storage under liiunidity conditions different from tliose 

 of manufacture or use. This investigation concerned itself princi- 

 pally with tlie various kinds of wood finishes and treatments with sub- 

 stances known to be water-resistant. Tests on many commercial 

 paints and varnishes sliowed that none of tliese were sufficiently re- 

 sistant to the passage of moisture through them, and there resulted 



