2 BULLETIN 145, U. S. DEPARTMENT OF AGRICULTURE. 



the deficiencies of present practice in wood preservation and pave 

 the way for increasing its efficiency by suggesting lines for orginal 

 research. 



From 40 to 90 per cent, or an average of over 60 per cent of the 

 total cost of treating wood, is chargeable to the preservative alone. 

 In ordinary treatments with coal-tar creosote it is common practice 

 to inject 5 to 10 pounds of the oil per cubic foot of wood, although 

 toxicity tests indicate that about one-half of a pound will prevent fun- 

 gous growth; in other words, exclusive of subsequent changes, from 10 

 to 20 times as much creosote is used per volume of wood as is theoretic- 

 ally required. The possibility of safely reducing this amount, and 

 consequently the cost of treatment, is one of the problems referred 

 to. The tests described herein should therefore be considered simply 

 as preliminary to the more difficult problems involved. 



PROPERTIES INVESTIGATED. 



The practical value of a preservative depends very largely upon 

 the conditions under which it is used, and investigations to deter- 

 mine its value must necessarily be broad. The following points 

 were considered in the tests: 



(1) The important chemical and physical properties of the pre- 

 servative. 



(2) The effect of the preservative on the strength of the wood 

 treated with it. 



(3) The ability of the preservative to penetrate and diffuse through 

 wood. 



(4) The permanency of the preservative after its injection into 

 wood. This involves a study of its volatility and leachability. 



(5) The combustibility of wood treated with the preservatives. 



(6) The toxic efficiency of the preservative in preventing the 

 growth of wood-destroying fungi. 



(7) The corrosive action of the preservative on steel. 



(8) The effect of the preservative on paint applied to the wood 

 subsequent to treatment. 



No systematic tests were made on the effect of the preservative 

 as an electrolyte or in contaminating drinking water, nor any tests 

 which relate to a special or limited use. 



METHODS OF TEST. 



The various tests were conducted as follows: 



Tho roughly air-seasoned eastern hemlock (Tsuga canadensis L.) 

 was selected as the wood best suited for the experiment because of 

 its low inherent resistance to attack by fungi, the comparative uni- 

 formity with which it can be treated, and its availability. Only 

 perfectly clear, straight-grained, and uniform material, free from all 



