COAL-TAR AND WATER-GAS TAR CREOSOTES." 57 
merit, and time of treatment were held constant. The equation is 
simplified by dividing through by these numbers, but it must not 
be lost sight of that they belong in the equation, and that the equation 
X Y = K holds only when M, P, and T are constant. 
VOLATILITY. 
There is, perhaps, no physical property of coal-tar creosote that 
is of greater interest to the wood-preserving industry as a whole than 
its volatility, because the permanence of the treatment is largely 
dependent upon the volatility of the creosote. Alleman (19), Von 
Schrenk (20)] Bateman (21), Ridgway (22), Rhodes and Hosford 
(23) , and Mattos (57) in this country have shown that the oils present 
in piling, ties, and poles, after long use, have contained large amounts 
of the higher-boiling fractions of creosote. The loss was restricted 
chiefly to that portion of the creosote which distilled below 245° C, 
although there was also an appreciable loss in the portion distilling 
between 245° C. and 270° C. Above 270° C, however, the oil seemed 
to be fairly permanent. It has been shown by the Forest Products 
Laboratory that, if the assumption is made that there is no loss above 
270° C, then the loss by evaporation may be calculated from an 
analysis of the original creosote and of the creosote extracted from 
wood that had been in service a long time. The correctness of this 
assumption is shown by the fact that calculations made from analyses 
of oil before and after use in open-tank treatment showed a loss of 41 
per cent. A record of the amount of creosote in the timber after 
treatment and the amount used during treatment showed that there 
had been at least 38 per cent of loss, or practically the same figure as 
calculated from the analyses. 
Instead of the residue about 270° C, some investigators had used 
the pitch residue, that is, the residue above 315° C. Although it 
is probable that, if the oils boiling above 270° C. are practically 
nonvolatile, then the pitch residues should possess this property to 
an even greater degree, yet, on account of the size of the fraction, 
calculations based on the pitch residue are more liable to error than 
those based on the residue above 270° C. This is because there is 
about the same accuracy in determining the pitch residue by weight 
as there is in determining the residue above 270° C. As the latter 
fraction is usually two and sometimes three or four times as great 
as the former, an error in determining the residue above 270° C. is 
only half as great on a percentage basis as would be the same error 
in determining the amount of pitch. This is shown very well by 
the following calculations. Creosote was allowed to evaporate in a 
pan and its loss was accurately determined. The analysis of this 
creosote before and after evaporation is given in Table 18. 
