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Eucalyptus Lumber 



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Abstract of Report by E. D. Tiemann, Forest Products Laboratory, 



Madison, Wis., U. S. Forest Service, Department of Agriculture. 



Tliere is a physical limit to the rate at wliieh auy piece of wootl 

 can be dried, which is the rate at whicli moisture can be transmitted 

 through tlie body of the wood 'itself. If the surface evaporation is 

 more rapid than the rate of transmission from the center outwards, 

 " casehardening " or surface drying results, inevitably followed by 

 honeycombing. 



It is supposed that temperature increases the rate of transmission 



r.\RT 11 



results were obtained, poorer grades might be tried. 



Two relatively large trees were selected for the first experiment, 

 from a grove in Piedmont, one a very thrifty tree two and one-half 

 feet in diameter and the other about two feet. Both were sawed 

 into inch boarils as soon as felled and sent immediately to the dry- 

 kiln. The boards were divided into three groups, and treated as 

 follows: 



1. Boards of the first group were all marked S, and were first 

 steamed at a slight pressure of one or two pounds for three and a 

 half hours, then doused in a tank of water at a temperature of 150 

 degrees. TJiey were left in the tank with the AV boards over night, 

 with a little heat turned on the keep the water warm. 



2. Boards of the second group, marked W, were put in cool water 

 which was heated to 140 degrees in twenty minutes, two hours before 

 the -S boards were introduced. 



3. Boards marked A were not given any preliminary treatment. 

 At nine next morning the temperature of the water in the tank 



containing the S and W boards was 194 degree F. At 2:15 p. m., 

 wlicn the boards were taken out and piled on the truck, it was 142. 

 .Tu.st twenty-five hours after the W boards were placed in the tank, 

 and twentv-thrce hours after the S boards were removed from the 



.SKCTIONS CUT FROM KILX-DEIED BLLE GIM B().\RDi<, SHOWINii 



HOW THE BOARDS W.\RP. C AND D ARE BOTH FROM THE 



SAME BO.VRD, C BEING ALL SAI' AND D MOSTLY HEART. 



of moisture through wood, hence tlie object in drying at as high 

 temperature as possible. But nothing definite is known in this regard. 

 Moisture travels away from the warmer toward the colder portions of 

 the wood, hence the necessity of having the lumber warm clear 

 through. 



All things being equal, the higher tlie temperature, with correct 

 humidity, the quicker and better the wood ought to dry. However, 

 many factors modify this deduction, especially with blue gum which 

 becomes very soft and punky when it is heated in the moist condition, 

 even below the boiling point; and above 212 degrees it resembles 

 putty to a surprising extent. It seems altogether improbable, there- 

 fore, that blue gum can be successfully dried at high temperatures. 

 Superheated steam would be entirely disastrous to this wood. When 

 the wood becomes dry the temperature may be considerably raised 

 without injury. It seems apparent from the eucalyptus experiments 

 that the high temperatures while moist greatly increase the amount 

 of shrinkage, so that the best results ought to be obtained by the 

 lowest temperatures. 



Al! woods partake of the nature of a colloid, as glue or gelatine, 

 to some extent, some species much more than others. Blue gum, at 

 least the smaller trees, partakes of this nature to an exaggerated 

 degree. In fact, it behaves more like glue in its hygroscopic relation 

 than it does like other woods. It has the remarkable property of 

 shrinking upon the slightest loss of moisture from the green condi- 

 tion, and continues to shrink at a steady rate until perfectly dry. 

 Other hardwoods show little or no shrinkage until they have dried to 

 their "fiber saturation" point, which generally lies between twenty 

 and thirty per cent moisture on a dry weight basis. With blue gum 

 the shrinkage begins at from seventy to eighty per cent moisture. 



In conducting this investigation it was decided to determine, first 

 of all, whether even the best of blue gum lumber could be dried 

 satisfactorily by the slowest and mo.st careful method. Then if good 



—20— 



I'JECE OF BLIE 01 .\I VENEER WIIICH ACTUALLY "WALKED 



AWAY." 



cylinder and doused in tlit tank, the trmk uas run into the first com- 

 partment of the kiln, designated "Section I." Sample pieces of 

 each were taken. Weights before and after treatment were: S be- 

 fore, twenty-nine pounds; after steaming and soaking, twenty-nine 

 and one-half pounds. W before, twenly-one and one-half pounds; 

 after steaming and soaking, twenty-two pounds. The conditions of 

 Section I of the kiln were: 



.lust after 

 placing In 

 Section L 

 .\t .'i :'JU p. m. .\t .1 p. m 



■iVin|iiT:itiuc near rooL west side *. . . 120° 126° 



Tempi-rature halfway up, west side ilW 129° 



Tomppratnrc under spray chamber, west ,sldo.... 117° 123° 



(dew point tcmperatnri' i 



Calculated humidH.v, west side -l',i 83% 



Humidity Ijy hair hygrometer, east sidi' .V.x;;',; S2% 



All boards marked A were placed on one truck and run into the 

 middle compartment, "Section II," of the kiln at 12:45 the same 

 day, after first thorougldy wetting the lumber with a hose. The con- 

 ditions in this section were: 



