332 



FORESTRY AND IRRIGATION 



July 



ing was done, though part of this area 

 remains to be planted next season. 

 This was to exclude stock. To ex- 

 clude prairie fires a fire guard was 

 ploughed about the plantation. 



Kiln Drying 



The Forest Service has 

 made a successful dem- 

 Dnstration of kiln-drying 

 tupelo, the experiment being under-> 

 taken in cooperation with a lumber 

 manufacturer in Louisiana, who deals 

 in tupelo, and with a wagon manufac- 

 turer in Michigan. The lumber was 

 cut in the former state and shipped 

 directly to the latter, where it was put 

 through the dry-kiln without prelimi- 

 nary seasoning. Tupelo is a wood 

 suited to many commercial uses, and 

 one to be profitably lumbered in con- 

 nection with cypress, with which tim- 

 ber it occurs. A drawback to the use 

 of tupelo has been the difficulty of sea- 

 soning, since it is subject to warping, 

 checking, and staining in the season- 

 ing process. Hence a demonstration 

 of success in kiln-drying the wood 

 without any of these defects is of 

 great value to the tupelo industry. 



In the experiments the kiln used is 

 that known as the blower type, op- 

 erated on the moist-air principle of 

 drying. The hot air is forced by fans 

 into the dry end, thence passes back 

 through the trucks of lumber to the 

 wet end, and is returned to the engine 

 room through a large drying chamber 

 over the kiln itself. The whole struc- 

 ture is as nearly air-tight as it can be 

 made ; consequently the same air, pass- 

 ing through the kiln and back over 

 the steam-heating coils, is used over 

 and over again. The necessary mois- 

 ture is obtained from the green lum- 

 ber as it is put into the wet end of the 

 kiln. 



The lumber should enter a temper- 

 ature of about 93 degrees Fahrenheit 

 at the wet end of the kiln. The tem- 

 perature gradually increases as the 

 truck moves toward the dry end- 

 where it should stand in a tempera- 

 ture of 140 degrees to 150 degrees 

 Fahrenheit for two or three days. In 

 the experiment described the average 



temperature of the wet and dry ends 

 was respectively 98 degrees and 133 

 degrees Fahrenheit. In this particular 

 case the relative humidity at wet and 

 dry ends was 84 per cent and 29 per 

 cent, respectively. 



As has been demonstrated in air- 

 drying, so in kiln-drying, the correct 

 piling of lumber is of utmost import- 

 ance. The piles on the trucks should 

 be arranged so that the spaces between 

 the boards are not obstructed by ad- 

 jacent courses, but remain open so 

 as to give an upward vent to aid the 

 circulation of the drying air. This 

 can be accomplished by piling the wide 

 boards apart from the narrow ones, 

 or by laying the wide boards so that 

 they do not extend over the open 

 spaces. The old method of piling nar- 

 row and wide boards together so as 

 to get horizontal and criss-cross cir- 

 culation, is satisfactory in the open air 

 where there are strong winds ; but in 

 a kiln, with only a few inches of space 

 about the stack for air circulation, the 

 lumber must be piled as openly as 

 economical operation of the kiln will 

 allow. 



The boards in this experiment were 

 from eight to twelve inches wide, one . 

 inch thick, and fourteen feet long. One 

 truck was piled with the cross strips 

 twelve inches apart, and another with 

 strips eighteen inches apart. Equally 

 good results were obtained by both 

 methods. The lumber was in the kiln 

 fifteen days, and when taken out was 

 dried satisfactory without molding, 

 staining, or stick-rotting. . Only one 

 board was checked as much as one 

 foot from the end, and none of the 

 other boards showed checks more than 

 half an inch in length at the ends,, 

 while most were not checked at all. 

 Five of the boards on the top course 

 were slightly warped. There was a 

 loss of 4,200 pounds, or one-third of 

 the green weight, and a shrinkage of 

 127.2 board feet or 4.4 per cent of the 

 original scale. 



The method here described is that 

 regularly used at this kiln in the dry- 

 ing of red gum, which occupied other 

 trucks at the same time. Thus it was 



