6 1 4 THE POPULAR SCIENCE MONTHLY. 



absorption of moisture. Woods impregnated with the heavy tar or 

 lighter oils are protected more from the fact of prevention of access 

 of dampness to the libers than by the contained antiseptics, unless in 

 the exception of a great percentage of creosote. In the second method 

 the moisture is permitted to come in contact with the fibers of the 

 wood, and reliance depends upon the antiseptic. In this case, the en- 

 tire wood should be saturated to give the greatest measure of success, 

 not merely an exterior protection of a half-inch or so in depth, the 

 latter fact, as before explained, being the cause of many of the fail- 

 ures which have taken place. The antiseptic treatment, to succeed, 

 must destroy all the germs which have found lodgment in the timber, 

 and also those which may come from the exterior. 



In a general paper I can only indicate the antiseptics which have 

 been fairly successful, though in many cases the failures were due not 

 so much to the antiseptic used as to the faulty manner of application, 

 which can be understood from w T hat has been written. 



The four antiseptics which are most used now are chloride of zinc, 

 creosote, corrosive sublimate, and sulphate of copper ; sulphate of iron 

 and pyrolignite of iron may be mentioned. The treatment of the wood 

 by bichloride of mercury (corrosive sublimate) was called kyanizing ; 

 by chloride of zinc, Burnettizing ; by creosote, creosoting or the Bethel 

 process ; by sulphate of copper, Boucherie's process. Sulphate of cop- 

 per has been used for over a century in preserving timber, and when 

 well applied the results have been good. The idea of Boucherie was 

 to force the antiseptic through all the wood-cells, which was correct, 

 and the method successful in proportion to the extent it was accom- 

 plished. 



The attempts to impregnate wood are made now with nearly all of 

 the antiseptics, in large cylinders capable of sustaining from two hun- 

 dred to three hundred pounds pressure per square inch, one end of 

 which can be opened and closed for admission and withdrawal of the 

 timber. When the cylinders are filled with the timber they are closed, 

 then steam or heat is applied to vaporize the sap or moisture ; after this 

 a partial vacuum is produced and sustained for from six to twelve hours, 

 then the moisture is withdrawn from the cylinders, and the antiseptic 

 is pumped in and raised to a pressure of from one hundred and twenty 

 to one hundred and fifty pounds, which is maintained for from six to 

 twenty-four hours. Porous woods are impregnated quite readily, 

 while the heart-wood of the yellow pine (see Fig. 1) and the white 

 oak (Fig. 3 in August number) are not penetrated so easily, and take 

 longer time. The external pressure may be one hundred and fifty 

 pounds per square inch ; yet the hydrostatic pressure in the cavities of 

 the cells, not l0 ^ 00 of an inch in area, is quite small, the impregna- 

 tion being to a great extent by capillary attraction and absorption 

 through the cell- walls. 



It is evident from preceding statements and illustrations that un- 



