TESTS OF WOOD PRBSEEVATIVES. 13 



the treated and untreated specimens; there was no visible evidence 

 of the hygroscopic action of zinc chloride on the paint film, nor did 

 the salt appear to come to the surface. There was a marked difference 

 in the appearance of the treated and untreated specimens that were 

 placed in running water for 1 year and 4 months. (See PL VI.) 

 The paint film on the one treated with sodium fluoride and the un- 

 treated one had disintegrated and could be rubbed off upon a cloth 

 (see PL VI, at top) ; that on the specimen treated with zinc chloride 

 was in good condition. This indicates that zinc chloride may have a 

 preservative action upon paint films under certain circumstances. 



No results have thus far been obtained from the last series of tests 

 made in cooperation with the National Paint Manufacturers' Associ- 

 ation. 



The results of the tests thus far made indicate that woods treated 

 with zinc chloride, sodium fluoride, and other water-soluble salts 

 might be successfully painted. This point can not be definitely 

 settled, however, until the results of the tests in cooperation with 

 the National Paint Manufacturers' Association become available. 



CONCLUSIONS. 



In general, highly viscous oils do not readily penetrate, while 

 oils with low viscosities penetrate wood readily. As temperature 

 strongly influences the viscosity of oils, and as the diffusion of the 

 preservative through the wood is one of the most important factors 

 in proper treatment, to secure best results both the wood and the 

 preservative should be sufficiently heated during the pressure period. 

 Because of the low thermal conductivity of wood the treatments 

 should not be made too rapidly. With water-soluble salts these pre- 

 cautions are not important. 



With coal-tar creosote it appears that the fractions of greater sta- 

 bility are the less toxic. Present practice rather favors the reten- 

 tion in treated wood of the more volatile fractions by an admixture 

 of the more stable ones. If the toxic values here given are correct, 

 there is, in practice, being forced into wood about one and one-half 

 times as much zinc chloride and from 10 to 20 times as much coal-tar 

 creosote as is necessary to prevent decay. Of course, in practice 

 more preservative than these toxic minima must be forced into 

 wood in order to make proper allowance for any subsequent changes 

 that might take place. However, more economic results, especially 

 when decay is accompanied by mechanical deterioration, can be 

 secured by diffusing the preservative more thoroughly through the 

 wood than by saturating the outer fibers and attempting to retain 

 in the wood the volatile constituents through admixtures of non- 



