Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/15

Rh stopped when the oily matter begins to acquire a brown colour, and when the production of acetic acid is less perceptible, the matter in the retort will be found when cold, to have assumed a solid consistence. In this state it resembles either pitch or asphaltum, according to the degree of heat it has undergone after it became capable of solidifying.

I will describe this substance as it appears when it first becomes solid, the reason of which will soon be apparent.

Previously to its arriving at this state, it bears a considerable resemblance to maltha, being of a consistence intermediate between that of petroleum and asphaltum, but I did not completely examine its chemical properties in this condition because they appeared not to differ from what might be expected, and its history will be sufficiently full without it. In the solid state it is brilliant and shining and breaks with a conchoidal fracture and some external resemblance to obsidian. It has a pungent burning taste and the well known smell of wood smoke. It is heavier than the specimen of asphaltum with which I compared it, having a specific gravity of 1.254, while that of the asphaltum was 1.202. It is fusible and readily inflammable, burning with a white flame. It is electric and exhibits the same electricity as the resinous bodies. When heated in an open vessel, it smokes, and if kept in fusion till it ceases to smoke, it at length ceases to be fusible and is ultimately converted into a coal. During this progress it becomes more brilliant and less fusible, its fracture also from conchoidal becomes more splintery, and it puts on the appearance of asphaltum so accurately that the eye cannot detect the difference. Its specific gravity also diminishes, and its chemical properties vary in the way I am now about to detail.

I have described the perfect solubility of the tar in alcohol. The