Page:Popular Science Monthly Volume 81.djvu/186

180 Agitation is provided by passing some of the live steam through the crude material while it is heating. When there is no further evolution of steam and the melted mass has become tranquil, it is drawn off from the bottom of the tanks into open cement barrels placed on flat cars. These are not filled at once, but are topped off after the first filling has cooled, so that there shall be no loss of material. The product obtained in this way is the refined asphalt of commerce, and is in shape for shipment to whatever point there may be demand for it.

It may be interesting to note that the amount of crude material shipped from Trinidad during recent years, has reached as high as 180,000

tons per year, while that from the Bermudez deposits has reached as high as 47,000 tons but is rapidly increasing. The entire amount shipped from Trinidad since 1867 has reached three million tons, which would be equivalent to 180 million square yards of sheet asphalt pavement.

Trinidad asphalt being for many years the only available supply of such material, it was the only one used in the early days of asphaltic highway construction in the United States. It has been subjected to the most varied environment with the most satisfactory results. There are in existence to-day three pavements which are worthy of consideration, as showing its capacity to meet different kinds of traffic and different climatic conditions.