78 bulletijST 1036, u. s. department of ageiculture. 



the tar-acid and tar-base contents, the deterrni nation of the ratio of 

 the specific gravities to the indices of refraction values of the various 

 fractions, and the testing of the toxicity of the creosotes. The 

 absence of tar acids or tar bases is proof that the oil under test is not 

 a distillate of coal tar. Part of the tar acids or tar bases may 

 be removed from coal-tar creosote by chemical methods, but it is 

 not likely that all the tar acids and all the tar bases would be taken 

 out by such means. On the other hand, the presence of tar acids or 

 tar bases or both classes of compounds does not mean that the oil 

 under examination is a pure coal-tar distillate. It may be a water- 

 gas-tar oil which has been mixed with a coal-tar creosote containing 

 large amounts of tar acids and bases, or these materials may have 

 been added directly to water-gas-tar creosote. The determination of 

 the ratio of the specific gravities of the fractions to their index of 

 refraction values is of use only if it is known that the distillates are 

 pure oils, either water-gas-tar or coal-tar distillates. Unknown 

 mixtures of the two can not be differentiated with certainty by this 

 method. The toxicity test is of value only in high-boiling oils similar 

 to carbolineum. In lower-boiling oils the fraction similar to car- 

 boliueum might be tested, but because of the fact that six weeks are 

 required for its completion this test is of little value for commercial 

 purposes. 



