Page:Popular Science Monthly Volume 58.djvu/245

Rh of these constituents are not always present and vary widely in amount when present, so that, from a chemical standpoint, the different asphaltums and the bitumens of the different asphaltes are very unlike substances. In the practical uses to which these substances are applied, the selection for any given purpose does not appear to depend upon difference of composition. The purest varieties are used for making fine varnishes and lacquers. Others are used for coarser varnishes that are baked on to iron and other surfaces. Others are applied, softened with solvents that evaporate. These substances find wide uses for insulating purposes, alone and in mixture with other materials.

The widest use to which they are applied is in street-paving surfaces, for which purpose vast quantities are used every year. It has been

found in practice that good streets and poor streets have been made from nearly all the different varieties of asphaltums and asphaltes that can be obtained in such quantity and at such a price as to render their use possible. The different results obtained appear to be due to causes external to the asphaltum or asphalte employed, such as the kind and quality of the materials with which they are mixed and the method, or lack of method, by which they are mixed. These conclusions appear to be warranted by a large number of experiments extending over many years, some of which have been very expensive for the municipalities making them.