The most important source of supply of asphalt for street pavements in the United States is that of the island of Trinidad, W. I. This asphalt is known as lake asphalt or land asphalt, according to the source from which it is obtained. Lake asphalt is found in a large deposit known as the pitch lake. This lake covers an area of over no acres, and lies in a deep crater with steeply sloping sides. The pitch seems to be, or to have been, forced up from below, and it is more or less in motion, excavations in the surface being gradu ally filled by flow of material from sides and bottom. Upon exposure to the air, the pitch slowly hardens, is somewhat softer near the center of the lake than at the sides, and it has been supposed that the supply from subterranean sources still continues to some extent. It has also been found that the surface of the lake is higher in the center than at the sides, and that the general elevation of the surface has been lowered somewhat by the large quantities of material which have been removed from it.
Refined Trinidad Lake Asphalt consists ordinarily of about 54 per cent to 57 per cent bitumen, 5 per cent to 8 per cent of organic matter not soluble in carbon bisulphide, and 35 per cent to 38 per cent of mineral matter. The bitumens contain about 63 per cent to 66 per cent of malthenes (according to Richardson's classification), the remainder being asphaltenes, with sometimes about 1 per cent of carbenes. These asphal tenes contain considerable sulphur and are hard, brittle substances, which do not melt but are readily soluble in the asphaltic oils. The non-bituminous
organic matter is mainly material which seems to have been formed through oxidation of some of the harder bitumens of the asphalt. It contains a considerable amount of sulphur and may be considered, like the finely divided mineral matter, as of use as filler. The mineral matter in Trinidad asphalt is found in a finely pulverized condition and quite uniformly distributed through the mass.
The so-called land asphalt from Trinidad is found in vicinity of the lake, and is a harder material than lake asphalt, probably from longer exposure to the air. It may have been derived either from the overflow of the lake or from independent subterranean sources, the action in which has long ceased.* Refined Trinidad Land Asphalt consists commonly of about 51 per cent to J5 per cent bitumen, 7 per cent to to per cent organic matter insoluble in carbon bisulphide, and 37 per cent to 4o per cent of mineral matter. The bitumen contains from 5o per cent to 63 per cent of malthenes, soluble in 88° naphtha solution.
The character of the land asphalt is more variable than that of the lake, and seems to depend upon the length of time it has been exposed to the weather. The bitumen of the asphalt undergoes a gradual harden-' ing with time, the percentage of malthenes becoming less as compared with that of the asphaltenes. In some instances the amount of mineral matter is greater, while the non-bituminous organic matter is increased by the changing of some of the bitumen to an insoluble condition.