COAL-TAR AND WATER-GAS TAR CREOSOTES. 



51 



VAPOR PRESSURE. 



In the course of some experimental runs made by the Forest 

 Service in a wood-preserving plant of light design, an explosion 

 occurred which resulted in the rupture of the cylinder. It was 

 thought at the time that, if the vapor pressure of the creosote oil 

 were found to be sufficiently great, it might be an important factor 

 in determining the design of treating plants. Experiments were 

 therefore made to ascertain this vapor pressure at least approximately. 

 Table 15 shows the average results obtained in experiments with two 

 creosotes of different characteristics. 



Table 



15. — Vapor pressure of coal-tar creosotes. 





Vapor pressure. 





Vapor presstire. 



Temper- 





Temper- 





ature 







ature 







(degrees 



Inches 



Poimds 



(degrees 



Inches 



Pounds 



C). 



of 



per 



C). 



of 



per 





mercury. 



sq. m. 





mercury. 



sq. m. 



50 



2.0 



1.0 



110 



7.4 



3.7 



60 



2.8 



1.4 



120 



8.2 



4.1 



70 



3.6 



1.8 



130 



9.0 



4.5 



80 



4.6 



2.3 



140 



9.8 



4.9 



90 



5.6 



2.8 



~ 150 



10.6 



5.3 



100 



6.4 



3.2 









This vapor pressure is not sufficient to do any material harm, 

 since it is always less than the atmospheric pressures at ordinary 

 temperatures and elevations. If, however, the creosote contains 

 water, the vapor pressure under this condition will be the sum of the 

 vapor pressures of creosote and water. The vapor pressure of the 

 mixture will be as shown in Table 16 if the vapor pressure of creosote, 

 as given above, is used: 



Table 16. — Vapor pressure of mixtures of coal-tar creosote and water. 





Vapor pressure. 





Vapor pressure. 



Temper- 

 ature 







Temper- 

 ature 









' 





(degrees 



Inches 



Pounds 



(degrees 



Inches 



Pounds 



C). 



of 



per 



C). 



of 



per 





mercury. 



sq. m. 





mercury. 



sq. in. 



40 



3.0 



1.5 



80 



18.6 



9.3 



50 



3.6 



2.7 



90 



26.2 



13.1 



60 



8.6 



4.3 



100 



36.4 



18.2 



70V 



12.8 



6.4 









In this case, even at 100° C, the vapor pressure in excess of atmos- 

 pheric pressure (15 pounds a square inch) is only 3.2 pounds a square 

 inch, which is a pressure so small that it need not be taken into 

 consideration in designing treating plants. 



SPECIFIC HEAT. 



It is frequently desiraole to know the specific heat of creosote in 

 order that allowance may be made for sufficient coils to heat the 



