82 BULLETI]S: 1036, U. S. DEPAETMEXT OF AGEICTOLTLTRE. 



Table 31. — Change in specific gravity of different mixtures of tar and coal-tar creosote. 



Mixture contains — 



Change 

 in specific 

 gravity per 

 degree Fah- 

 renheit. 



Tar. 



Creosote. 



Per cent. 

 10 

 20 

 30 

 40 

 50 



Per ceni. 

 90 

 80 

 70 

 60 

 50 



0. 00042 

 .00042 

 .00041 

 .00041 

 .00040 



VOLATILITY. 



The question has been raised whether or not evaporation can be 

 partially prevented by the addition of some such nonvolatile material 

 as tar, the tar having some sort of binding or holding property which 

 would prevent the creosote from evaporating as rapidly as if it were 

 used alone. In one of their papers, Von Schrenk and Kammerer {25) 

 give a number of curves showing the loss by evaporation of creosote, 

 tar, and creosote-tar mixtures. The tests extended over a long 

 period of time, namely, 1,000 days, or nearly 3 years. The curves 

 show that the tar is less volatile than the creosote-tar mixtures, and 

 that the latter are less volatile than the creosote. If, however, the 

 results are plotted in the same way as those of the creosote test 

 (fig. 31), the same relation between volatility and percentage of 

 distillate up to 270° C. will be shown. Furthermore, the volatihty 

 of the creosote-tar mixture can be calculated from the known vola- 

 tility of the creosote and tar. The calculation is extremely simple 

 and consists in multiplying the volatility of each constituent by the 

 percentage used in the mixture and taking the sum of the two products 

 as the volatilitj' of the mixtures. Calculations made in this manner 

 show the results given in Table 32. 



Table 32. — Comparison of actual and calculated losses due to evaporation of tar and 



coal-tar creosote mixtures. 









Calcu- 





Loss of 

 creosote. 



Loss of 

 tar. 



Tar mixtures. 



lated 



loss of 



mixtures. 



Actual 

 loss. 



Per cent. 



Per cent. 



Per cent. 



Per cent. 



Per cent. 



4S.8 



9. a 



70p. ct. C, 30p. ct. T. 



37.0 



38.0 



46.2 



9.0 



80p. ct. 20p. ct. 



38.8 



40.4 



46.2 



9.0 Vap. ct. 30p. ct. 



35.0 



37.8 



65.0 



6.0 ! 80p. ct. 20p. ct. 



53.2 



51.8 



50.8 



5. 6 : 80 p. ct. 20 p. ct. 



41.8 



41.8 



59.6 



10. 9 80 p. ct. 20 p. ct. 



49.8 



48.6 



Table 32 shows that the actual loss and the calculated loss are 

 practically identical. In other words, the effect of the tar is simply 

 to reduce the quantity of creosote in the test, and the percentage 



