Material Employed

The American petroleum at first came over for the most part between 28° and 95°, and was richest in hexanes ; the weight of distillate between 56° and 74° was about 800 grams. Aromatic hydrocarbons were not removed before the fractionation by treatment with nitric and sulphuric acids.

From the Galician petroleum, the hydrocarbons boiling below 40° and above 72° had previously been for the most part separated by distillation, and benzene was removed before the fractionation was commenced. The weight of the Galician petroleum was about 5 times as great as that of the American.

Still-Heads Used

The fractionation of the American petroleum was carried out with a 12-section Young and Thomas bubbling still-head, that of the Galician with the combined bubbling and regulated temperature still-heads which were employed for the separation of the pentanes (Fig. 53, p. 150).

The Galician petroleum was thus freer from pentanes and heptanes to begin with than the American, and the still-head employed was more efficient.

Description Of Results

In Table 78 are given the temperature ranges and the values of for the fourth fractionation of the American petroleum, and it will be seen that at this early stage the fraction from 65° to 66° has the highest value, but in the subsequent fractionations the ratio for the corresponding fraction (above 65°) steadily fell, and after the tenth fractionation this fraction had the lowest value.

Table 78

Graphical Representation

So far as the middle fraction is concerned, the gradual change in the value of closely resembles that observed in the case of the two pentanes, but in other respects the fractionations show marked differences, which become apparent when the curves (Fig. 82) representing the separation of the hexanes are compared with those for the pentanes (Fig. 36, p. 113).

As the quantity of Galician petroleum was much greater than that of American, the weight of distillate coming over between 60° and 70° has been taken as 100 for both of them in each fractionation, and as the tenth and sixteenth fractionations of American petroleum correspond very closely with the fourth and seventh respectively of the Galician, only one curve has been drawn for each of these two pairs, the experimental results for American petroleum being indicated in these and other cases by crosses, and for Galician by circles. The fractionations of American petroleum are referred to as Iva, XA . . . and of Galician as Ivg, Viig . . .

After the fifth fractionation of the pentanes. the values of for the lowest and highest fractions show a steady rise, until, in the thirteenth fractionation, the last portion of liquid boiled quite constantly at 36.3°, and, in the eighteenth, the first portion of distillate came over quite constantly at 27.95 ; in other words, the curves became quite horizontal at these two temperatures.

Fig. 82. - Results obtained by fractional distillation of American and of Galician petroleum. (Fractions from 58° to 72°.).

Highest Fractions

With the hexanes, on the other hand, no fraction was obtained with perfectly constant boiling point even though, in the case of American petroleum, the liquid which came over above 66° was fractionated thirty-one times. Indeed, after the sixteenth frapfirmntinn the maximum value of

(at about 69.1°) showed very little further rise, and after the twenty-first fractionation it diminished slightly.

With the Galician petroleum, no further improvement in the value of for the fraction a little above 69o was noticeable after the eleventh fractionation.

Lowest Fractions

Again, at the lower temperatures, in the case of American petroleum, the highest individual value of was reached in the twelfth fractionation (189 for the fraction coming over between 60.85° and 61.0°). In the sixteenth fractionation, the highest value had fallen to 141 for the fraction from 60.75 to 60.9, but, on the other hand, the values for the fractions above and below these temperatures showed a tendency to rise.

With Galician petroleum the highest individual value of at the lower temperatures was reached in the eleventh fractionation (790 for the fraction from 60.6° to 60.85°). In the last fractionation, the seventeenth, the maximum was only 626 for the fraction coming over between 60.55° and 60.75°, but in this case also the values for the higher and lower fractions appeared to be increasing slightly.