COAL--TAR AND WATER-GAS TAR CREOSOTES. 



75 



for the three curves in figure 35 are, 



(1) F=5i|2(io)!; (2) r=Mao)i' (3) y^ 



TOXIC PROPERTIES OF WATER-GAS-TAR CREOSOTES. 



8.94(10)" 



One might expect that the toxicity of water-gas-tar creosotes 

 would be somewhat less than the toxicity of coal-tar creosotes 

 because of the absence of tar acids and tar bases. This, in general 

 seems to be true. The killing points of a few authentic water-gas-tar 

 creosotes produced in the Forest Products Laboratory vary from 0.3 

 per cent to approximately 1 per cent against the timber-destroying 

 fungus Fames annosus. Dean and Downes (30) have investigated 

 water-gas-tar creosotes and compared them with coal-tar creosotes. 

 Their investigations with the timber-destroying fungus Polystictus 

 versicolor show that the water-gas-tar creosotes used in their tests 

 were about as toxic as the coal-tar creosotes which they used. These 

 investigations also showed that the coal-tar cresosote, after being 

 freed from tar acids and tar bases, was only two-thirds as toxic as the 

 original creosote or the water-gas-tar creosotes with which they 

 compared it. The water-gas-tar creosotes were about twice as toxic 

 as the high-boiling anthracene oils obtained from coal tar. J. M. 

 Weiss (31) has shown that water-gas-tar creosotes are not so toxic 

 against yeast, molds, and bacteria as the coal-tar creosotes which he 

 tested. 



The work of these investigators may be criticised not only because 

 of their method of determining the toxicity, but also because they did 

 not compare creosotes of similar boiling points. Dean and Downes, 

 for instance, compared the toxicity of creosotes having the distilla- 

 tion limits shown in Table 28. 



Table 28. 



-Comparison of the percentages of distillates of the creosotes whose toxicities 

 viere compared by Dean and Downes. 



Fraction. 



Coal-tar 

 creosote. 



Water-gas- 

 tar creosote. 



Up to 205° C . . . 

 Upto240°C... 

 Up to 300° C... 

 Up to 320° C... 



Per cent. 



6.5 



37.2 



58.5 



67.6 



Per cent. 

 10.0 



45.5 

 78.0 

 84.0 



The water-gas-tar creosote has a much lower boiling point than has 

 the coal-tar creosote, and, consequently, it should be more toxic 

 than the neutral oil of the coal-tar creosote. Weiss compared the 

 oils as shown in Table 29. 



