ts Beaead fF é st _) ie fei tc A ae 
ae ae ie 
R TESTS OF WOOD PRESERVATIVES. 13 
» aa 
_ the treated and untreated specimens; there was no visible evidence 
of the hygroscopic action of zine 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 zine chloride 
: was in good condition. This indicates that zine 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 
4 with zine chloride, sodium fluoride, and other water-soluble salts 
eemment be Piedad ally painted. This point can not be definitely 
settled, however, until the results of the tests in cooperation with 
the National Bent Manufacturers’ Association become available. 
CONCLUSIONS. 
In general, highly viscous oils do not readily penetrate, while 
eis 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 
ee ser vative 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 zine chloride and from 10 to 20 times as much coal!-tar 
x reosote as is necessary to prevent decay. Of course, in practice 
ore 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 retam 
in the wood the volatile constituents through admixtures oi non- 
