ASPHALT. The general term asphalt is applied to the several varieties of hydrocarbons of an asphaltic base which exist in all condi tions from the liquid to the solid state. It is more specifically employed to include the purer forms of hard and soft bitumen, such as elater ite, albertite, gilsonite, nigrite, wurtzilite, brea, etc. The term bituminous rock includes sand stones and limestones impregnated with bitu men or asphalt. This rock, usually shipped without previous refining, is used principally for street pavements and is mixed with other ingredients at the place of use.
The importation of asphalt into the United States is chiefly from the island of Trinidad, off the coast of Venezuela, and from Venezuela itself. Bituminous limestones are imported from Neuchatel and Val de Travers, in Switz erland, from Seyssel in France, and in small quantities from Germany, Italy,. Russia, Austria Hungary, Spain, Turkey in Asia, Great Britain, the United States of Colombia, Canada, the Netherlands, Cuba and Mexico. The total im ports from Trinidad and Venezuela in 1916 amounted to 147,383 short tons. The island of Trinidad, one of the British West Indian pos sessions, is the largest producer of asphalt in the world. The deposits are operated by an American corporation under a concession from the British government, and also, independently, from land not belonging to the Crown, ac quired by purchase. The chief source of sup ply is a lake of pitch. This lake lies 138 feet above the sea-level and has an area of about 114 acres. The supply is partly renewed by a constant flow of soft pitch into the centre of the lake from subterranean sources. The ship ments of this lake pitch average over 140,000 tons per year, and the flow into the lake is at the rate of about 20,000 tons per year. The depth of this lake is about 135 feet at the centre. Distinct from the lake pitch is what is known as °land the overflow in past times of pitch from the lake, and deposits of similar nature. During recent years strenuous efforts have been made to discredit all asphalt mined from properties located outside of Pitch Lake. These efforts seem to have failed, how ever. Careful analyses of samples of asphalt
taken from different parts of Pitch Lake, from deposits outside the lake and from the of La Brea show that these asphalts are so similar in composition that for practical pur poses they may be considered as identical in quality. The samples have a common origin, for the presence of mineral matter in these asphalts cannot be regarded as adventitious, since it is thoroughly incorporated with the bitumen in the same proportion and has the same percentage of composition, as regards the relative proportions of matter soluble in water, in acids and insoluble substances. There is no doubt that the pitch found in the deposits out side the lake has been derived from the lake itself by the subterranean flow of pitch in the viscous condition. It is true there is a differ ence in the crude materials in these asphalts; one is softer than the other, because of con taining more volatile ods. Nature simply be gan on the asphalt outside the lake; it being more exposed to the rays of the tropical sun, the process of refining it drove those volatile oils off, a necessary accomplishment to make the material fit for paving purposes. It would appear, therefore, that a part of the labor of refining has been done on the land or overflow asphalt which remains to be done with the lake asphalt.
In 1875 the asphalt paving industry was in its infancy in the United States. In 1903 there were about 42,000,000 square yards of asphalt, sheet and block, which has been laid at a cost of about $110,000,000. These pavements are frequently called bituminous pavements, inas much as bitumen is the largest constituent of the asphalt, frequently running as high as 9 per cent. Asphalt is manufactured into a ce ment by mixing it with other forms of bitumen and this cement is in turn used to bind to gether particles of sand and limestone in the asphalt pavement. No two asphalts are alike. The life of the pavement depends upon the crude bitumen used, the skill in its manufac ture into bituminous cement, the proper pro portioning and mixing of the cement with the sand and dust and in the selection of the min eral aggregate.