COAL-TAR AND WATER-GAS TAR CREOSOTES, 57 



ment, and time of treatment were held constant. The equation is 

 simphfied by dividing through by these numbers, but it must not 

 be lost sight of that they belong in the equation, and that the equation 

 XY ^ 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 acciu-acy in determining the pitch residue by weight 

 as there is in determining the residue above 270° C. As tlie 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. 



