36 BULLETIN 1037, U. S. DEPARTMENT OF AGRICULTURE. 
substances have given more or less satisfactory results (Weiss and 
Barnum, 57). In wet weather, however, it has been found necessary 
practically to double the strength of the solutions. Moreover, both 
sodium carbonate and sodium bicarbonate cause a yellow to brown 
discoloration of the wood. Lumber treated with these preservatives 
must be open piled or it may mold and stain badly during warm, 
humid weather. 
A good grade of sodium carbonate in the form of soda ash should 
contain 58J per cent alkali, while the amount present in sodium bi¬ 
carbonate (baking soda) is about 37 per cent. Solutions of the latter 
are more or less decomposed at temperatures above 158° F., giving off 
carbon dioxid. In a series of laboratory experiments followed by 
practical field tests on southern yellow pine and red gum, Rumbold 
(37) found that the blue-stain fungus is sensitive to alkalis but not 
to acids, that an 8 per cent solution of sodium carbonate is as effec¬ 
tive as an 11 per cent solution of sodium bicarbonate, and that the 
amount necessary to prevent growth varies with the substratum. 
Freshly cut sapwood of southern yellow pine or red gum required 8 
per cent sodium carbonate and 10 per cent sodium bicarbonate solu¬ 
tions under conditions which were especially favorable for the growth 
of the blue-stain fungus. In dry weather a weak solution of the 
alkali (a 5 per cent solution of sodium carbonate and a 4 per cent 
solution of the bicarbonate) kept the yellow pine boards free from 
stain. It was also observed that the spores of the blue-stain fungus 
are more resistant than the mycelium. These experiments seem to 
show that sodium carbonate and sodium bicarbonate possess some 
value as a preventive against sap-stain but that the success attending 
the treatment is largely dependent upon weather conditions. 
SODIUM FLUORID, SODIUM BIFLUORID, AMMONIUM FLUORID. 
Sodium fluorid, which has proved to be very toxic to wood-destroy¬ 
ing fungi (Teesdale, Ifl), has also been tested to determine its 
toxic properties in connection with the blue-stain fungus. Represen¬ 
tatives 22 of the Forest Products Laboratory, working independently 
and in cooperation with certain lumber mills located in Mississippi 
and Louisiana, found that both sodium fluorid and sodium bifluorid 
were effective against sap-stain. The fluorids have an advantage 
over sodium carbonate and sodium bicarbonate in that they do not 
discolor the timber. One of these investigators, in a comparative 
series of experiments with a number of preservatives, including 2J 
per cent sodium fluorid, 2£ per cent sodium bifluorid, and 2J per cent 
ammonium fluorid, found that in the concentrations mentioned these 
salts were fairly effective against sap-stain. The ammonium fluorid, 
n Unpublished reports by Pettigrew and Knowlton in the files of the Forest Products 
Laboratory, Madison, Wis. 
