REVIEWS 



Tests of the .Ibsorption and Penetration of Coal Tar and Creosote 

 in Longleaf Pine. Bull. No. 607, U. S. Dept. of Agri.. June 7, 1918. 

 r>y Clyde H. Teesdale and J. D. McLean. 



This bnlletin describes a series of tests to determine the effect of tlie 

 addition of coal tar to creosote upon the ease of injection of the pre- 

 servative into longleaf pine, especially in the treatment of paving blocks. 

 Two methods were employed to secure this information, through the 

 use of the "penetrance apparatus'" devised by members of the staff of 

 the Madison Laboratory of the L\ S. Forest Service, and by treating 

 paving blocks of the usual size in an experimental retort. Six com- 

 mercial coal-tar creosotes from different sources and five coal tars from 

 by-product ovens and gas-house plants were used in the tests. Carbon- 

 free tar was obtained by the chloroform solution method, which has 

 l>een subjected to some discussion. A pressure of 75 pounds per s(|uare 

 inch was used in the penetrance apparatus, this pressure being main- 

 tained for two hours at a temperature of 160°. The blocks were treated 

 in the experimental retort under varying conditions until a uniform 

 penetration or absorption of 16 pounds per cubic foot was obtained in 

 each instance. Various mixtures of creosote, carbon-free tar, and 

 unfiltered tar were used, and from the results of the treatment the fol- 

 lowing conclusions are drawn : 



The addition of coal tar to the creosote increased the difficulty of 

 injection, which became proportionately more difficult as tars contain- 

 ing free carbon in increasing amounts were used in the mixtures. Tars 

 containing small free-carbon ])articles increased the difficulty of injec- 

 tion more than tars containing larger free-carbon particles. The vis- 

 cosity of mixtures of coal tar and creosote does not appear to be an 

 index of the ease of injection of such mixtures into longleaf pine. The 

 most important factors influencing penetration appear to be — 



1. The character and composition of the bitumens. 



2. The amount of free carbon in the tar. 



3. The condition and size of the free-carbon ]^articles. 



It was found that by increasing the temperature of the preservative 

 the ease of injection of the preservative was materially increased. The 

 reviewer wi.shes to call attention to the fact that this apparent discrep- 

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