120. Varieties

One of the groups of mineral substances composed of different hydro-carbons, which are widely scattered throughout the world, is known as bitumen. There is a great variety of forms in which bitumen is found, ranging from volatile liquids to thick semi-fluids and solids. These are usually intermixed with different kinds of inorganic or organic matter, but are sometimes found in a free or pure state. Liquid varieties are known as naphtha and petroleum; the viscous or semi-fluid as maltha or mineral tar; and the solid as asphalt or asphaltum.

121. Asphaltum

The most noted deposit of asphaltum is found in the island of Trinidad and at Bermudez, Venezuela. Deposits of nearly pure asphaltum are found in Utah, Mexico, Cuba, and different parts of the United States. Varieties of nearly pure asphalt are known as wurtzilite, elaterite, and gilsonite.

' The main source of supply of asphaltum used in the United States for street paving, has been the Trinidad deposit. This is also the main source for asphaltic roofing materials.

122. Asphalt

The bituminous limestone deposits at Seyssel and Pyrimont, France; in the Val-de-Travers, Canton of Neuchatel, Switzerland; and at Ragusa, Sicily, are known as rock asphalt. It is more durable than asphaltum, and is extensively used in Europe for paving purposes.

There are two forms in which rock asphalt is prepared for shipment:

(a) Compressed asphalt blocks, which are used in about the manner of stone blocks.

(b) Mastic asphalt, which is made into blocks of different sizes, generally bearing the manufacturer's trade mark.

The mastic asphalt is used for waterproofing and damp-proofing purposes. For all work of this kind, the Val-de-Travers, or the Seyssel, or Sicilian rock asphalt should be used.