146 THE SCHOOL BOOK OF FORESTRY 



twenty to forty days. The kiln-dried lumber is 

 just as strong and useful for construction as 

 the air-cured stock. Tests have proved that 

 kiln drying of walnut for use in gun stocks or 

 airplane propellers, in some cases reduced the 

 waste of material from 60 to 2 per cent. The 

 kiln-dried material was ready for use in one- 

 third the time it would have taken to season the 

 material in the air. Heavy green oak timbers 

 for wagons and wheels were dried in the kiln 

 in ninety to one hundred days. It would have 

 taken two years to cure this material outdoors. 



By their valuable test work, scientists are de- 

 vising efficient means of protecting wood against 

 decay. They treat the woods with such chemicals 

 as creosote, zinc chloride and other preservatives. 

 The life of the average railroad tie is at least 

 doubled by such treatment. We could save about 

 one and one-half billion board feet of valuable 

 hardwood lumber annually if all the 85,000,000 

 untreated railroad ties now in use could be pro- 

 tected in this manner. If all wood exposed to 

 decay were similarly treated, we could save about 

 six billion board feet of timber each year. 



About one-sixth of all the lumber that is cut 

 in the United States is used in making crates 



