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. 

 Freshlj^ 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, AMMONIUil FLUOKID. 



Sodium fluorid, which has proved to be very toxic to wood-destroy- 

 ing fungi (Teesdale, ^), has also been tested to determine its 

 toxic properties in connection with the blue-stain fungus. Represen- 

 tatives ^^ 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 2^ 

 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, 



" Unpublished reports by Pottigrew and Knowlton in the files of the Forest Products 

 Laboratory, Madison, Wis. 



