A NATIONAL PLAN FOB AMERICAN FORESTRY 677 



commonly used methods, and in others require the adaptation of exist- 

 ing machinery, if not the development of entirely new machinery. 



CONDITIONING FOR USE 



The work so far done on the conditioning phase of utilization has 

 consisted largely of the various problems connected with the drying 

 of wood and particularly of lumber. That on kiln drying has pro- 

 gressed far beyond an initial studv of different species with standard 

 apparatus and methods. The principles of the kiln-drying process 

 have been developed and applied in improving commercial methods 

 and apparatus to the extent of practically revolutionizing such prac- 

 tices. The fundamental "how and why" of moisture movement in 

 wood during drying have also been studied. Air-seasoning methods 

 and results have been investigated. The work on methods of drying 

 has been supplemented by investigations on allied subjects, such as 

 the change in moisture content of dried lumber during storage and 

 handling, the normal variations of moisture content of wood in 

 houses, and rapid methods, including equipment, for determining 

 moisture content. 



A complete understanding of the "how and why" of moisture 

 movement and of moisture relations in general is one of the most im- 

 portant and complex lines of research ahead in forest products and 

 once obtained will have outstanding value in many different ways 

 such, for example, as the further improvement of methods of kiln 

 drying and air seasoning, the development of methods for treating 

 wood which will prevent the absorption of or loss of moisture and 

 hence shrinking, swelling, checking, etc. Similar work will un- 

 doubtedly be necessary on modified materials such as pulp and paper, 

 and on some wood products other than lumber. 



GRADING AND SELECTION 



Lumber grading has been the first crude attempt to select or 

 classify lumber according to value, and obviously value has some 

 relation to properties. Grading has been based entirely on readily 

 visible differences in amount and kind of defects without reference to 

 properties other than those obviously affected by the defects. Ex- 

 cept in the rules for structural timbers, the grades have borne no 

 quantitative relationship to any specific property. Forest Service in- 

 vestigations on grading have been devoted partly to the relation be- 

 tween strength and grades in structural timbers, but mostly to the 

 standardization of grading rules for different species, which have 

 varied so widely and have been so complex that they have been very 

 difficult for the public to understand or use. 



Selection among species to obtain the best wood for every use is a 

 much more important and complicated technological problem. In 

 fact, it consists of such a large number of separate problems that only 

 a few of them have been investigated directly. General information 

 on the requirements for various uses, together with that on the prop- 

 erties of the different species, must be correlated to obtain proper 

 selection. This subject will be brought up again under "Properties. " 



It will be apparent that a sound scientific basis is available for 

 lumber grading only in part. The only product other than lumber 



