102 WOODWORKING 



Two or three coats of coal-tar creosote oil are necessary, 

 and all surfaces exposed or in contact with moisture-collecting 

 materials, such as concrete, should be covered. Particular 

 attention is directed to the covering of surfaces of joints, such 

 as the sides of mortises and tenons, etc. 



89. The Open-Tank Process, while not feasible under 

 ordinary farm conditions, is here briefly described, that it 

 may be used where conditions permit. It consists of alter- 

 nate hot-and-cold treatments of wood with refined coal-tar 

 creosote oil by immersion and continuous soaking in open 

 tanks without artificial pressure, requiring no mechanical ap- 

 paratus other than tanks, hoist (in some cases), and means of 

 heating the oil. 



The procedure is as lollows: Season the lumber suffi- 

 ciently to expel any excess of moisture. When cut for sizes, 

 construction, etc. that is, when completely framed im- 

 merse lumber in a bath of coal-tar creosote oil maintained at a 

 temperature of from 150 to 210 degrees F. for a period deter- 

 mined as follows : For close-grained wood (naturally resist- 

 ant to impregnation), one hour in the hot and one hour in the 

 cold, or cooling, bath for each inch of the largest cross-section. 

 For species more susceptible to treatment, one-quarter of an 

 hour for each inch of the largest cross-section, and milled lum- 

 ber from ten to thirty minutes in each bath ; or, if the stock is 

 in the form of boards, an immersion of a few minutes is suffi- 

 cient. Frequently, heavy-milled stock is not subjected to 

 the cold-bath treatment, but allowed to remain in the hot 

 bath after the source of heat is removed and while the oil 

 cools. On the other hand, boards are not subjected even to a 



