6 



BULLETIN 606, U. S. DEPARTMENT OP AGRICULTURE. 



mirror D, placed at the back of the oven, it was possible to observe 

 both ends of the specimen during the test. 



The impregnation tests were made in a cylinder L| feet in diameter 

 and 4 feet long. Temperature and pressure were controlled by means 

 of steam coils and a pressure pump. The specimens were separated 

 from each other during treatment, so that all parts of the wood were 

 in contact with the preservative. 



MATERIALS USED. 



CREOSOTE. 



The creosote used was a coal-tar product with a specific gravity of 

 1.071 at 140° F. (60° C.) and a viscosity, determined by the Engler 

 viscosimeter, of 1.2 at 160° F. (71° C). The distillation 1 was as 

 follows : 



Temperature. 



Distil- 

 lation. 



° C. 

 0-205 



Per cent. 

 1.2 



22. 7 

 5.7 

 9.9 



11.5 



205-235 



235-245 



245-275 



275-305 



305-360 



27.6 



Residue 



20.9 

 .5 



Loss 



Total 



100.0 



The creosote was obtained by distilling a by-product coke oven 

 tar (Semet Solvay) to a very hard pitch. The indices of refraction 

 at 60° C. and sulphonation tests are rather low for a pure coal-tar 

 creosote, probably because the tar was produced in comparatively 

 low-temperature ovens. The residue was a soft, sticky pitch, indi- 

 cating the presence of a small amount of undistilled tar (probably 

 less than 5 per cent) . 



WOOD. 



The wood used in the experiments was selected from 25 species 

 of hardwoods. In order to make the results comparable, all of the 

 specimens for the different experiments on a given species were 

 taken from the same log and matched as closely as possible. Most 

 of the specimens used in the tests were heartwood, as sapwood speci- 

 mens of sufficient size were available from only four of the species 

 used. 



1 For method of analyses see Forest Service Circular 1S8, p. 36. ■ 



