4 BULLETIN 145, U. S. DEPARTMENT OF AGRICULTURE. 



PENETRANCE OF THE PRESERVATIVE INTO WOOD. 



The distribution of a preservative in the wood, a most important 

 feature in any treatment, was studied as follows: 



The central portions of sticks 4, 5, and 6, after the strength data 

 had been obtained on them, were split, and the depth and character 

 of the penetration recorded. This could usually be done visually, 

 but with those preservatives which in aqueous solution were color- 

 less, an aniline dye was used or the specimens were chemically 

 analyzed. 1 



The results from these tests were used to supplement those secured 

 from pieces 8, 9, and 10, which were tested in a specially-constructed 

 penetrance apparatus (see PL II) operated in the following man- 

 ner: A hole 1 inch in diameter was bored in the center of each stick 

 (A) to a depth of three-fourths inch. The stick was then placed on 

 the shelf (B) inside the apparatus for several hours, and after being 

 weighed was clamped between two iron disks ( and D) so that the 

 preservative could be forced into the hole from the tank (E) under 

 a constant pressure and temperature. The stick was raised to a 

 temperature of about 180° F. by the steam coils (F) before the pre- 

 servative was admitted. The pressure was controlled by compressed 

 air on the top of the preservative in tank ( E) . For oils, the length 

 of the pressure period was 30 minutes, and for water-soluble salts 3 

 minutes, with the exception of sodium silicate, for which the time 

 was prolonged to 30 minutes. The time it took to penetrate the 

 wood longitudinally was noted. 2 At the end of these periods the 

 specimen was sawed longitudinally and transversely through the 

 center lines and the penetration radially, tangentially, and longitudi- 

 nally was studied. (See PL III.) 



VOLATILITY TESTS. 



The volatility tests on oils were made to determine only the 

 relative rates at which they left the treated wood. The plan of 

 using matched pieces, as outlined in Plate I, was abandoned because 

 the data obtained were inaccurate, the specimens reabsorbing 

 moisture through the untreated end surfaces of the specimens cut 

 after treatment. A new set of specimens was prepared from noble 

 fir (each l\ by 2 by 6 inches) and treated for the volatility experi- 

 ments. These were weighed separately and placed in the volatility 

 apparatus (fig. 1), consisting of an air-tight metal box, 15 by 24 by 

 30 inches, through which a constant current of air, partially dehy- 

 drated by passing through calcium chloride towers, was drawn. 



1 It was found by repeated tests that -water and the dye had a tendency to penetrate in some cases 

 slightly farther than the preservative, although the difference was of no practical significance. 



2 A mirror placed in the back of the apparatus enabled the penetration in the rear end of the stick to be 

 determined. 



