74 BULLETIN 909, TJ. S. DEPARTMENT OF AGRICULTURE. . 



pose. Ash, mahogany, oak, and some other woods are used for these 

 propellers at the present time in the United States. The propeller 

 blades are built up of several plies of wood glued together. Extreme 

 care must be taken in making propellers, for any slight warping or 

 opening of a glued joint may render the propeller worthless. Pro- 

 peller stock should be seasoned by special methods, and the different 

 laminations should be approximately of the same density and the 

 same moisture content. The laminations are kept under constant 

 moisture conditions for several days .prior to gluing. Propellers 

 are first finished to the exact form and afterward are balanced. The 

 ends of the blades are often tipped with a strip of sheet copper, and 

 the propeller is covered with varnish or some other preparation to 

 protect the wood. Walnut for airplane stock must be of the highest 

 grade and entirely clear. Wide lumber, usually 1 inch thick, is de- 

 manded. Statistics are not available on the amounts of black walnut 

 consumed in the industry or on the average prices paid for what 

 was used. The United States, through the Bureau of Aircraft Pro- 

 duction, paid during the war as much as $310 a thousand board feet 

 for black- walnut propeller stock, and this was considered a very high 

 price at that time. 



EXPORT. 



Exportation has always played an important part in the walnut- 

 lumber industry. European countries early recognized the value of 

 the timber, particularly for cabinetwork. It is claimed that black- 

 walnut timber was shipped to Europe as early as 1629. War con- 

 ditions have interfered with its exportation during the past few 

 years. During the year 1918 its shipment from the United States 

 in the form of the log and for any but war uses was stopped, and, 

 on account of the disturbed conditions abroad, exportation is still 

 considered below normal. However, the amounts exported are now 

 steadily increasing. 



Walnut is exported in the form of both logs and lumber. Table 24 

 gives the amounts of logs and the total and average values for dif- 

 ferent years, by countries. Similar data are not available for lumber. 

 Records of walnut-lumber exports for the year 1912 show that ap- 

 proximately 75 per cent of the total lumber output of the large wal- 

 nut producers was exported during that year. According to the 

 calculated amounts shown in the section on " Demand " this exporta- 

 tion amounted to about 31 million feet, which would be distributed 

 about as follows : Germany, 50 per cent, 15.5 million board feet ; 

 British Isles, 35 per cent, 10.85 million board feet; other countries 

 (principally Denmark. Scandinavia, Holland, Belgium, and Spain), 

 15 per cent, 4.65 million board feet. During the first six months of 



