Peckham and Linton — Trinidad Pitch. 193 



Art. XX. — On Trinidad Pitch; by S. F. Peckham and 

 Laura A Linton. 



The bitumen found on the Island of Trinidad in the so- 

 called Pitch Lake and in its neighborhood, has entered com- 

 merce under the name of Trinidad Pitch. That which is 

 found within the lake is called " Lake Pitch ; " that found 

 outside the lake is called " Land Pitch." 



As it occurs it is a unique substance found nowhere else in 

 nature. It consists of a mixture of bitumen, water, sand, 

 decayed vegetation and gas in such definite proportions that 

 within certain limits the composition of the entire mass is 

 uniform. The bitumen has never yet been investigated in 

 such manner as to determine its relations to other bitumens, 

 but it appears to be of vegetable origin and convertible into 

 solid asphaltum by processes of nature. In its natural condi- 

 tion about one-third of it is water. Deprived of water it is 

 about one-third sand. When the bitumen is dissolved away 

 from the sand under the microscope, the silica appears to be in 

 exceedingly minute amorphous particles from -y§\-§-§ to l 1 Q 

 of an inch in thickness. "When freed from organic matter by 

 burning, the silica appears in small sharply angular grains, 

 stained by iron and a small quantity of bluish clay. The 

 organic matter not bitumen consists of fragments of vegetation 

 and disorganized cellular tissue, with products of the decompo- 

 sition of wood. 



As the bitumen rises in the center of the so-called lake it is 

 inflated with gas. When the masses are broken into the 

 structure resembles vesicular lava. The gas cavities are of all 

 sizes, some of them very large and in the aggregate occupy at 

 a rough estimate from one-third to one-half the volume of the 

 pitch. At any point in the deposit removed from the center 

 of the lake, the gas, in part, has escaped from the asphaltum 

 and the mass become more compact. Both within and with- 

 out the lake the pitch is saturated with water. It is in this 

 condition without viscosity and can be trodden upon or 

 squeezed in the hands without adhesion to either hands or feet. 

 In this condition it cuts like cheese, hence the name, " cheese 

 pitch." When freshly dug the color is brown, but if left in 

 the sun it soon darkens, finally becoming a bluish-black. If a 

 mass of any considerable size is laid in the sun, it will melt to 

 a thin pellicle upon the exposed surface, and retain the larger 

 part of the water at a temperature sufficient to remove every 

 trace of water if it were dried in the shade. A mass exposed 

 to the air out of the sun, immediately begins to dry out and 



Am. Jour. Sci. — Fourth Series, Yol. I, No. 3. — March, 1896. 

 13 



