32 The Forest Products Laiwratorv 



esses in vogue. Recognizing that, after all, any failures to succeed 

 with the more difficult conditions imposed by the demands of industry 

 for wider application of kiln drying, were simply attributable to a 

 lack of fundamental knowledge of the physical properties of the wood 

 to be dried, the laboratory from the beginning made kiln drying one 

 of the leading studies. The study centered on the physics of timber 

 and, as a natural auxiliary, a study and consequent development of 

 apparatus to perform the drying operation. 



The outstanding features of kiln drying as developed in the past 

 ten years at the laboratory are : first, absolute control of moisture and 

 temperature conditions in the entire kiln or any part of it at any stage 

 of the drying; second, an exact knowledge of physical changes taking 

 place in the lumber in the kiln throughout the run; and third, the per- 

 fection of means of diagnosing these changes and applying any cor- 

 rective measures necessary in case adverse conditions develop. 



The natural result of these ten years of study has been a notable 

 contribution to the knowledge of timber physics, the invention and 

 development of several types of kilns and auxiliary apparatus that 

 have been quite widely adopted in the fields of kiln drying where they 

 are especially suited, the extension of kiln drying with its economic 

 advantages to new fields and the elimination of much loss that had 

 been taken mistakenly for granted in kiln drying practice. 



Schedules for proper drying with practically no loss from de- 

 grade, have been developed for many species and sizes of material 

 from dimension oak to smaller sizes of pine. As to the kilns, the water 

 spray and superheated steam types are largely of laboratory develop- 

 ment, and they have received the main attention considering the ob- 

 jectives in mind. 



Fundamental data on the structure of wood, as revealed under 

 the microscope, serve as foundation for many laboratory studies, and 

 for the identification of wood as to species through examination of the 

 wood itself rather than by a study of the botanical characteristics of 

 the tree. Authentic specimens of most of the trees native to this 

 country have been collected, and microscopic slides made showing 

 radial, tangential, and cross sections. These have been studied and 

 analyzed and a key constructed, by which it is possible to distinguish 

 most commercial species. This key and the slides are in constant use 

 in the identification of samples of wood submitted by organizations 



