UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE
FOREST PRODUCTS LAORAIMN U ,MN,'V;- QYFL LI P
MADISON 5. WISCONSIN i 5
I . i .
DETERMINING PENETRATION OF WOO PRESERVATIVES
The effectiveness of any wood-preservative treatment is measured very
largely by the depth to which the preservative penetrates. This depth
can be determined by the following tests, which are used by the Forest
The presence of creosote, creosote mixtures, or other dark-colored
oils is indicated by the dark discoloration of the wood, and the degree
of penetration may readily be determined by taking a sample at a point
freefrom checks and other imperfections and at a considerable distance
from the end of the stick. This may be done either by making a hole
with an ordinary 1/2-inch bit and measuring the penetration on the wall
of the hole, or by using an increment borer to bring out a core of wood
that shows in cross section the depth of penetration and is easily exam-
ined. The observation should be made at once, because the oil spreads
rapidly over the cut surface, particularly over the end grain of the wood.
With low-viscosity oils, it is often desirable to examine a tangential or
radial section of the treated wood rather than an end-grain section. In
order to prevent infection, the hole in the treated piece should be tightly
closed with a thoroughly treated plug.
No entirely reliable method has been found for determining the depth of
penetration of pentachlorophenol when used in colorless or light-colored
oil solvents. In boring cores from wood recently treated, it is often
possible to distinguish the "wet" treated portion from the untreated por-
tion of the boring. Some degree of success in determining penetration
has been obtained by dusting a mixture of 20 parts of calcium carbonate
and 1 part of oil-soluble reddye lightly on freshly cut wood sections be-
fore the oil has an opportunity to spread.
Because zinc chloride is colorless, the depth of penetration of this pre-
servative must be ascertained by chemical means. The most common
method of determining penetration on a cut face or boring consists in
..... : .1.: Iy : u'h ii
,. 1%' .'"
spraying over the freshly cut surface a mixture of equal parts of a 1 per- .
cent solution of potassium ferricyanide, a 1 percent solution of potassi- 1
urn iodide, and a 5 percent solution of soluble starch. This mixture
colors the treated portion a very dark blue, but does not affect the un-
treated wood. Although the color fadesg in time, it may be brought back
by spraying again. This method may also be used to determine pene-
tration of chromated zinc chloride.
Sodium fluoride is colorless, but its presence in wood can be determined
by the following methcd. Make one solution (1) in the ratio of 5 grams
of zr4rconium oxychloride in 500 cubic centimeters of water. Make
another solution (2) in the ratio of 2 grams of sodium alizarine sulfonate,
40 cubic centimeters of concentrated hydrochloric acid, and 460 cubic
centimeters of water. The two solutions are kept separated until ready
for use, when a quantity of solution 2 is added to an equal quantity of
solution 1. It is essential that solution 2 be added to solution 1 rather
than vite versa. The cut surfaces or borings are sprayed or dipped in
the mixed solution. The treated wood will turn yellow, and the untreated
wood will become dark red. This method is also recommended by the
proprietors of some patented fluoride -phenol-dichromate preservatives
to measure the penetration of the sodium fluoride.
Mercuric chloride is also colorless, but dipping the wood in a solution
of hydrogen sulfide turns the treated area black.
The penetration of preservatives containing copper salts, such as Green-
salt (Erdalith or Ascu), Celcure, and Chemonite, can usually be ob-
served without the aid of a special stain. The following stain is useful,
however, for determining the penetration of these preservatives: Dis-
solve 0. 5 gram of 5-diphenyl carbazide in 50 cubic centimeters of iso-
plopyl alcohol and 50 cubic centimeters of water. When a boring or
cross section of treated wood is sprayed or dipped in this solution, the
presence of the copper compound is indicated by a purple color, and the
untreated wood shows little change.
As individual pieces may show an abnormally high or low degree of pene-
tration, a sufficient number of tests should be made to obtain a fair av-
erage. Samples should betaken at a considerable distance from the ends
of the stick, in order that they will not be "--'- ir thp heavy longi-
tudinal penetration from the ends. UNIVERSITY OF FLORIDA
II3 1262 09216 7393
3 1262 09216 7393
Agr Iculture-Mad Ilon