Page:Popular Science Monthly Volume 81.djvu/179

Rh exudes and some gas cavities are found in the general mass of the pitch beneath the crust. As the asphalt below the crust of the deposit is the only portion of value for paving, the question has arisen as to its uniformity.

An examination of a series of samples collected in 1894 shows that the asphalt from the Bermudez deposit may vary very largely in the amount of water which it contains, from 11 to 46 per cent. None of it, however, is present in the form in which it occurs in Trinidad asphalt. It is not emulsified with the bitumen, but is all adventitious surface water. The percentage of oils which it volatilizes at about 400° F. varies from 16 to 6 per cent., consequently the consistency is far from uniform. The material carefully selected for use industrially is fairly constant in character, however, and when carefully refined has the following proximate composition: