UTILIZATION OP BLACK WALNUT. 33 



the saw. The older method was that of piling the lumber in a pit 

 made of boards, at the bottom of which was the open end of the 

 exhaust-steam pipe from the engine. The lumber was then covered 

 over with sawdust and kept in the wet steam for several days. (PL 

 IV, fig. 1.) The common method now is to build one or usually 

 several large, fairly tight compartments with large doors and, after 

 the lumber is piled in these compartments, to close them as tight as 

 possible and turn in the steam. This method has the double effect 

 of giving the wood, including the sapwood, a uniformly brown color, 

 and of expediting the process of seasoning. There is usually not 

 sufficient exhaust steam for this purpose, and live steam also must 

 be used. Operators ordinarily steam their stock from four to five 

 days at a temperature of 140° to 160°. If live steam is used it is 

 difficult to regulate the temperature with the usual equipment; for 

 when little exhaust steam is available more live steam must be used, 

 and a higher temperature results. To regulate the moisture and tem- 

 perature of the steam there is an equipment used in which the live 

 steam is run over tanks of water ; as moisture is taken up, the tem- 

 perature is reduced. 



Forest Service tests on walnut steamed for 10 days at a tempera- 

 ture of 190° and at atmospheric pressure have shown a decided 

 loss in shock- resisting ability, or " toughness," for the steamed mate- 

 rial. It is likely, however, that no appreciable loss in strength prop- 

 erties results from steaming at the usual lower temperatures. Cab- 

 inetmakers report that they find little or no difference between the 

 properties of steamed and unsteamed walnut as it is now placed on 

 the market. 



Steaming gives a more or less uniform color to both heartwood 

 and sapwood and makes the sapwood as valuable on the market as 

 heartwood ; for, according to the grading rules, any amount of sap- 

 wood is admitted in steamed walnut. Steaming also shortens the 

 seasoning period. Manufacturers claim that steamed walnut, prop- 

 erly piled and air-seasoned, in 30 days will be as dry as unsteamed 

 green walnut that has been in the pile for 90 days. Steamed walnut 

 lumber 1 inch thick is considered to be " shipping dry " after being 

 air-dried 30 days; and l-§-inch steamed walnut is so regarded after 

 being air-dried 45 days, or one week for each quarter inch in thick- 

 ness. This procedure effects a great saving in the time required for 

 seasoning. It is also claimed that the steamed lumber is not so sub- 

 ject to fungus attack and discoloration when it is piled for air-drying. 



The amounts of different grades of lumber produced from walnut 

 logs are very difficult to determine, because no two manufacturers 

 use the same general class of logs for lumber, nor do they manufac- 



7434°— 20 3 



