COAL-TAR AND WATER-GAS TAR CREOSOTES. 
75 
for the three curves in figure 35 are, 
(1) V- 
6.02(10) 31 
(2) V- 
3.4(10) 31 
(3) V- 
8.94(10) 17 
TOXIC PROPERTIES OF WATER-GAS-TAR CREOSOTES. 
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 Forties 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 
v)ere compared by Dean and Downes. 
Fraction. 
Coal-tar 
creosote. 
Water-gas- 
tar creosote. 
Up to 205° C. 
Up to 240° 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. 
