P=^=^ (6) 



M aA 

 and, substituting Equation 5 in Equation 6, 



(7) 



In the calculation of the portion of oil remaining after the 

 weathering of Navy distillate fuels by means of Equation 7, the volatile 

 portion was considered the portion boiling below 298°C and the nonvolatile 

 portion that boiling above 298°C. The results obtained are shown in Table 

 4. The calculated results were generally somewhat high. Because some of 

 the nonvolatile portion will nevertheless evaporate, it would be expected 

 that the values of A^ would be somewhat low and that P would be somewhat 

 high. The results were especially high for the initial 6-week experiment 

 with Oil C, giving a value of 0.781 for the portion remaining, whereas 

 the recovery of the oil was 74.7%. In this longer evaporation, a higher 

 proportion of the nonvolatile hydrocarbons were probably lost. 



For residual fuels or for crude oils. Equation 7 cannot be used, 

 because the higher boiling components are not completely recovered in 

 the gas chromatography. For the evaporation of crude oils, Sivadier 

 and Mikolaj therefore developed a more complicated equation which involves 

 the areas between the C-|y and C28 hydrocarbon peaks, comprising components 

 boiling between 300°C and 431°C [7]. These ''truncated residues'' are 

 assumed to be nonvolatile and their areas, A^_, are used analogously to 

 A^ to establish the proportionality between the area factors, b/a, of the 

 gas chromatograms . Their equation for the weight fraction of oil evapora- 

 ted, F, also includes the portion of volatiles originally present in the 

 oil, Q°, as determined by distillation up to 288°C: 



F = Q° 1 - -^^^ (8) 



The evaporative weight losses calculated from the gas chromatographic 



data and the losses obtained from direct weighing of oil samples evaporated 



in dishes in the laboratory agreed within 1%. 



The above agreement was better than that obtained for the Navy 

 distillate fuels by use of Equation 7. This may be due partly to the fact 

 that the ''truncated residuum'' was much larger and of higher average 



15 



