January 10, 1922 



HARDWOOD RECORD 



61 



could be only possible with an outdoor temperature of 35° and out- 

 door humidity of 30%. If, then, this outdoor air were heated to 

 70°, a 10% relative humidity would result. 

 The Conclusions 

 Summing up, we must conclude that our correspondent's trouble 

 with glucd-up stock may come from several causes, single or in com- 

 bination, all explained in the preceding paragi-aphs, together with 

 proper remedy. These are: 



(a) Casehardening strains, not properly released after kiln drying 

 by steaming. Drying perhaps too rapid, without attention to actual 

 moisture content. 



(b) Kiln drying not uniform. Certain portions of the piles which 

 receive poor circulation do not dry as fast as the rest of the lumber, 

 passing to shop unnoticed and unchallenged. 



(c) Final moisture content of lumber not properly ascertained 

 and considered before lumber is removed from kiln, since the letter 

 states final humidity of kiln at 30%, which would hardly produce 

 a 3% moisture condition in the lumber, because the 30% moisture 

 condition of the air would balance a 6% moisture content in the 

 lumber. Inner moisture of lumber too high for the purpose to 

 which lumber is put. Too short a time in tempering shed. 



(d) Reabsorption of moisture from the air after kiln drying, in 

 the dry storage or tempering shed. 



(e) Air too dry in shop and finishing rooms for the moisture 

 actually in the wood when it has been manufactured, causing fur- 

 ther drying on the shop floor. 



Without closer investigation, at long distance, carefully consider- 

 ing the statements of the letter, the writer would advise investiga- 

 tion along the items, o, c and e, diagnosing the trouble as caused by 

 casehardening strain, in combination with high internal moisture, the 

 later drying out in the dry air condition of the shop floor, in which 

 case the remedy would be: Drying to only 5% moisture content of 

 the inner section of the board, plenty of samples before removal, 

 enabling definite knowledge of the actual inner condition of the 

 boards, longer time in dry storage, if possible, with right moisture 

 condition there, and an increased humidity condition of the air in the 

 work room, about 70° dry bulb and 53° wet bulb, which will equal 

 30%, and therefore will put a little moisture into the wood, but 

 not too much before finishing, since 30% would correspond to about 

 6% moisture in the wood, after long exposure. However, careful 

 investigation along items 6 and d possibly may also prove interest- 

 ing and profitable. 



Kiln Drying Course for Home Study 



Since the aunouncement of the correspondence study course kiln drying 

 of lumber liv the Extension Division of the University of Wisconsin less 

 than two years ago, almost 400 persons have enrolled. This course has 

 been developed through co-operation of the United States Forest Products 

 Laboratory. Men from thirty-seven states of the Union and seven foreign 

 countries have taken up this mail instruction to learn more about the 

 art of operating dry kilns and the proper handling of lumber in general. 



The distribution of the students according to states reflects fairly well 

 the location of the lumbering and wood-using industries. The registration 

 runs as follows : Indiana. 39 ; Wisconsin, 37 ; Michigan, 35 ; California, 

 23; Illinois, 10; New York, IS; Pennsylvania, 13 ; Missouri, 12; Wash- 

 ington 12 ; Louisiana, 11 ; Kentucky, 10, and all other states, 109. The 

 registration from foreign countries includes 16 from Canada, and one each 

 from Mexico. Panama, Porto Rico, England, China and Xew Zealand. 



This correspondence-study course is an outgrowth of the resident short 

 courses which have proved so successful at the United States Forest 

 Products Laboratory, located on the university campus. It was early 

 recognized that much of the information on improved methods of kiln 

 drying could be taught by mail. Many men who cannot .avail themselves 

 of the class instruction in kiln drying given at regular intervals at Madison 

 enroll for the correspondence-study course and so obtain valuable infor- 

 mation upon the latest developments in the seasoning of wood. 



The course consists of ten assignments prepared in a systematic way, 

 taking up the subjects from the structure of wood, its moisture content, 

 shrinking and casehardening, on through a discussion of the various types 

 of kilns, heat, humidity, circulation and the operation of kilns. Drying 

 schedules for all of the more common kinds of wood are included. 



The Extension Division of the University of Wisconsin, Madison, will 

 gladly supply Information on request. 



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