24 



THE POPULAR SCIENCE MONTHLY 



flaked out with picks, in large conchoidal masses weighing from 50 to 

 75 pounds. It is honeycombed with gas cavities, and resembles in 

 appearance the structure of a Swiss cheese. The gas evolved by the 

 pitch consists of hydrogen sulphide and carbon dioxide, but in such pro- 

 portions that it burns readily when a match is applied, although the 

 flame is not maintained for any length of time. 



In the center of the so-called lake is a point where there is a con- 

 tinued influx of soft material, accompanied by a stronger evolution of 

 gas, which gradually hardens and becomes like the remainder of the 

 deposit. The point of evolution of the soft material moves about from 



Photo, W. H. Rau, Philadelphia. 

 Winning the Crude Pitch, Refinery in Distance. 



place to place along lines of least resistance. As that evolved at one 

 point hardens the fresh material breaks out elsewhere. It is peculiar 

 in that it is associated with so much free water which rises with it, that 

 it can be handled freely and made into a ball without adhering to the 

 hands. It is in an active state of change, since if it is sealed in a tin 

 can the gas evolved will, in a few weeks, burst the containing vessel. 



The temperature of the pitch at the surface is no greater than that 

 of the surrounding air except when it is exposed to the noon-day sun, 

 when it may rise to 130° F. or over. That of the soft pitch is no higher 

 than any other pait of the deposit. 



