PETROLEUM AND NATURAL GAS IN NEW YORK 405 



asphalt. The probable order of their derivation is not the order 

 given above. From petroleum as an original center the other 

 three substances are seen to be easily derivable by natural and 

 familiar processes. From deep-stored oil when brought to day 

 natural gas is always given off. By the removal of the gaseous 

 hydrocarbons, the gravity of the petroleum is increased and the 

 process of oxidation sets in, the effect of which is to darken the 

 oil and still further reduce its gravity. We advance but a little 

 way along this line before we begin to withdraw the name of 

 petroleum from the dark and viscous liquid that we find result- 

 ing and give the substance the more appropriate designation of 

 mineral tar. It is also called maltha, which is an ancient and 

 somewhat technical designation. 



Now, if the mineral tar is still further exposed and oxidized, it 

 loses its liquidity altogether and hardens into a black solid, dull 

 or shining, as the case may be, called asphalt. 



Further, the petroleum from which the latter products are 

 derived has itself a wide range in gravity. Some examples of 

 it run as light as 55° B. while in other cases heavy oils of less 

 than 20° B. occur. In the latter case it is always possible to 

 explain the facts by the loss of the volatile elements as they 

 approach the surface. All shallow oils, under which designation 

 are included the occurrences of petroleum within one or two 

 hundred feet of the surface, are heavy. Some of them are too 

 viscous to flow freely and are well adapted in the natural state 

 to lubricating purposes. 



Not only does the fact that gas, maltha and asphalt are easily 

 derived from petroleum poiDt to the latter as the original sub- 

 stance, but the facts as to the chemical composition of oil and 

 gas respectively lead to the same conclusion. Natural gas con 

 sists essentially of light carburetted hydrogen (CH^), while 

 petroleum has a much more complex composition. The simplic- 

 ity of the former points to it as the derived substance. It is 

 therefore necessary to account for the origin of petroleum only. 

 All its derivatives will be explained under the same head. 



The subject has proved a tempting one for consideration and 

 as the economic importance of the series has increased it has 

 commanded more and more attention, till there is at the pres- 

 ent day a voluminous literature devoted to it. In regard to the 



