Product No. 4 was more decidedly yellowish than the last, but was in no other respect distinguishable from it.
Product No. 5 was more highly coloured, thicker in consistence, and had a decided empyreumatic odour.
Product No. 6. This and the two subsequent products were each more highly coloured and denser than the preceding. The last product had the colour and consistency of honey, and the odour was less penetrating than that of the preceding oils. The mass of crude product remaining in the retort (equal 47.4 per cent.) was a dark, thick, resinous-looking varnish, which was so stiff when cold that it could be inverted without spilling. This showed no disposition to harden or skin over by exposure to the air. The distillation was arrested at this point in glass, by our having reached the limit of temperature for a bath of linseed oil. The density of the several products of this distillation shows a progressive increase, thus:
Density Density
733
800 752 848 766 854 776 To form an idea of the comparative density of these several products, it may be well to state that sulphuric ether, which is one of the lightest fluids known, has a density of .736, and alcohol, when absolutely pure, .800.
The boiling points of these several fluids present some anomalies, but are usually progressive, thus, No. 2 gave signs of boiling at 115° C. (=239° F.), and boiled vigorously and remained constant at 225° C. to 228° C. (=437° to 442° F.). No. 3 began to boil 120° (=248° F.), rose to 270° (=518° F.), where it remained constant. No. 4 began to vapourise at 140° (=284° F.), rose to 290° (=554° F.), where it remained constant. On a second heating the temperature continued to rise, and passed 305° (=581° F.). No. 5 gave appearance of boiling at 160° (=320° F.), boiling more vigorously as the heat was raised, and was still rising at 308° (=581° F.). No. 6 commenced boiling at 135° (=275° F.), boiled violently at 160° (=320° F.), and continued rising above the range of the mercurial thermometer. No. 7 commenced ebullition at the same temperature as No. 6, and rose to 305° (=581° F.), where the ebullition was not very active. Much time was consumed in obtaining these results. We infer from them that the rock-oil is a mixture of numerous compounds, all having essentially the same chemical constitution, but differing in density and boiling points, and capable of separation from each other, by a well-regulated heat.
The uncertainty of the boiling points indicates that the products obtained at the temperatures named above were still mixtures of others, and the question forces itself upon us, whether these several oils are to be regarded as educts (i.e., bodies
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