ASPHALT. 207 



climate and grade for any job in any city. It will stand a higher 

 temperature without deterioration than other asphalts with more 

 bitumen. 



Bermudez Asphalt. — Although probably derived from the 

 same oil horizon as the Trinidad Pitch Lake this deposit differs 

 in its physical but not chemical characteristics. It is softer and 

 more ductile, and contains about 95 per cent, bitumen. The 

 deposit is about 140 miles due west in an air line from the Trinidad 

 deposit, is about 1,000 acres in extent, but much shallower, being 

 9 feet at the deepest part. It gives no evidence of being in constant 

 motion as the Trinidad deposit does, but is probably fed by several 

 springs of maltha over a large expense of territory. On account 

 of its softer consistency a smaller amount of flux is needed to bring 

 the asphalt cement to the same penetration as one made with 

 Trinidad asphalt. Also because of its greater bitumen content, a 

 less amount is. required in making a bituminous mixture, but a 

 larger amount of dust for filler must be added by the less effective 

 dry method, and then it is not as complete as the Trinidad colloidal 

 material. On the other hand its freedom from colloidal clay gives 

 it a lower melting point (about 180° F.) and a penetration of 

 about 20°. It also makes a better material for producing a 

 bituminous macadam by pouring the hot material on crushed stone 

 in the construction of country roads and highways. Its physical 

 similarity to Trinidad bitumen is shown by its tenacity in adhering 

 to stone, and staying where it is put for a number of years, which 

 is due to the quality of the bitumen, for it, like Trinidad, has 

 taken hundreds of years to arrive at the solid consistency necessary 

 for a basis to work from. It is similarly refined and fluxed. 



Various characteristics show that the bitumen of these two 

 lake asphalts is very similar, and that they are probably derived 

 from the same petroleum. One of the most notable characteristics 

 is the comparatively large amount of sulphur (6 per cent.) that 

 exists in a firmly combined state, whereby the otherwise unsatur- 

 ated hydrocarbons are made saturated compounds, assisted probably 

 by a polymerization and condensation of the molecules, and are 

 therefore in a condition of stable equilibrium. This tends to keep 

 them "alive" when laid as a pavement, and satisfactorily accounts 

 for the long life of the structure with a minimum of repairs. 



Oil Asphalt. 



Oil occurs in different forms and composition in various parts 

 of the world, and probably more generally than is usually sus- 

 pected. It occurs in two forms, natural and artificial, and by the 

 latter term is meant of pyrogenetic origin, such as the oils obtained 

 by the destructive distillation of wood, coal, fats and certain 

 shales. It will be therefore readily surmised that oils occur of 

 very different chemical composition. The natural oils may be sub- 

 divided according to whether they occur on or in the earth. The 

 former include the animal and vegetable oils, and the latter the 

 petroleums, or mineral oils, ignoring their probable or improbable 

 ultimate origin. It is with these latter that I propose to deal in 



