ASPHALT. 



205 



made by mixing clay into a slurry with water and adding it in 

 that state to the hot liquid asphalt; then heating to 250° F., and 

 stirring until the water is all expelled. It is then cooled and made 

 into a spiral, and put into the test-tube. In the sample that is 

 deformed and shows no stability the dry clay is mixed into the 

 hot liquid asphalt at 250° F., and stirred at that temperature for 

 the same length of time as the other; then it is cooled and made 

 into a spiral and put in a test-tube just as the other sample was. 



Exactly the same proportions of the same ingredients are used 

 in each case, and as the tubes are always being kept side by side 

 they are at all times under similar physical conditions ; yet the 

 "wet" mix (Nature's method at Trinidad) shows its original spiral 

 form, while the "dry" mix (man's method at the plant) has com- 

 pletely deformed, and shows only indications of its original spiral 

 form. The presence of this colloidal clay in Trinidad asphalt may 

 be demonstrated by immersing a piece in distilled water for about 

 two weeks. At the end of this time it will be noticed that the 

 asphalt is covered with a brown powder, which may be washed 

 .away, exposing the unaffected bitumen underneath. The explana- 

 tion of the phenomenon is as follows: — Each particle of the col- 

 loidal clay in a perfectly dry state is enclosed in a thin film of 

 bitumen. The water, by osmosis, passes through this film and 

 moistens the anhydrous clay, which therefore expands and bursts 

 the enclosing film, allowing the hydrated clay to escape. If this 

 is washed away, the film of bitumen remains adhering to the 

 unaltered underlying material ; or if the surface is heated the 

 bitumen is melted, the water evaporated, and it resumes its former 

 condition. The question might arise, if water has this effect upon 

 Trinidad refined asphalt why does it resist for so long the com- 

 bined action of atmospheric and traffic influences 1 The question 

 is answered by the above explanation, which gives the conditions 

 in an exaggerated form, for no street remains under water for a 

 •couple of weeks. In the course of time the liberated clay is 

 removed by the street cleaning gang while the bitumen remains in 

 the form of a thicker film. This decreases the action of osmosis, 

 so the surface is ultimately sealed and the water action stopped 

 without affecting the stabilizing action of the colloidal clay. 



The origin of the Pitch Lake is not very evident, but taking 

 it in connection with what is known of the surrounding country 

 and of other localities, an explanation, at least plausible, can be 

 afforded. An inspection of the map shows the country has been, 

 and still is, volcanic, as evidenced by the eruption in Martinique 

 in 1906, the more recent one of San Salvador in 1917, and the 

 still more recent one of Irazu in Costa Rica in 1919. Where 

 volcanic agencies are sleeping but not dead, the springs are fre- 

 quently warm, even boiling, and if superheated become solfataras. 

 These outlets may be many miles from the source of their heat 

 deep down in the earth, and therefore under great pressure. In 

 passing to that outlet these streams may encounter a stratum of 

 clay, or other fine mineral matter, through which they tear their 

 way, take up the earthy matter, and become the mud-springs, such 



