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V O L U M E 19, NO. 6
After the sample was charged and the overhead fractions were +egregated, the remainder of the sample, consisting entirely of hydrocarbons, \yas distilled a t the fastest rate possible in order to obtain a product balance. I n some cases maximum voltage \vas placed on the heater and y a r m air blown upward inside the vacuum jacket. S o att’emptwas made to control the distillatioii rat,e other than hy the automatic valves, which were controlled only by column pressure fluctuations. The amounts of C2, C3, C1, and Ci and heavier hydrocarbons determined by distillation in the first series of analyses (sample a) checked so closely that mass spectrometer analyses were obtairied on all succeeding total samples to verify the distillation results. ;is the program progressed i t was decided that a further check of the analyses should he obtained. Therefore, the samples \yere analyzed by lox-temperature fractional distillation using the distillation rates recommended by t,he Office of Rubher Reserve (3). The complete results of overhead analyses by mass spectronieter and total sample analyses by distillation and mass spectrometer are shown in Tables I and 11. The nominal charging rates used were 100, 150, and 250 cc. per minute. Because of the pressure drop through the system 250 cc. per minute nominal rate was the maximum found practicable with this equipment employing no more than 2 pounds inlet pressure. The total amount of sample charged was the same for every sample within practical limits (approximately 2000 mm. of chart travel = 5500 ml. of gas). Interpretation of the data obtained in this study reveals the following:
1. Varying amounts of methane are taken overhead a t the different charging rat’es, but in no case does i t appear that too high concentrations are included in the overhead fractions to be accurately determined by the usual combustion methods. The total C1 and overhead fractions, calculated t o a total sample basis, were found to be essentially the same when determined a t each of the various charging rates employed. 2. The heavy hydrocarbons found in the overhead fractions hy maqs spectrometer analysis are shown in the right-hand col-
unins of Tables I and 11, calculated on the basis of per cent of the gas charged to the apparatus. While the heaiy hydrocarbons found would cause a positive error in the Cp percentage and a negative error in the CI percentage, the actual amounts of the heavy hydrocarbons determined to be present in any of the samples a t any of the charging rates employed are so low that the cxffect of this contamination of the C1 and Cp constituents is within the accuracy attainable by the Burrell or L-. S. Steel methods of :inalysis for C1and Cp hydrocarbons. 3. S o advantage is shown for s l o ~charging rates over the fwtest practical rate (250 cc. per minute). 4. Reproducibility of quantities of individual fractions is csxcellent a t the fast distillation rates used and is in good agreement v i th the slow distillation and mass spectrometer analyses of the samples. For samples in which the C,,, C p ,C3, C,, and.
