120 GENESIS OF NATURAL GAS AND PETROLEUM. [Feb. 5, 



Mendeleeff's hypothesis implies that the production of natural 

 gas still continues, there being no reason to suppose that the iron or 

 other metallic carbides below the earth's surface are exhausted. 

 Consequently much importance must be attached to the question of 

 the presence of free hydrogen. 



Accepting provisionally the hypothesis of Mendeleeff, it may be 

 asserted that if natural gas is a contemporaneous product sufficient 

 time has not yet elapsed for the escape by diffusion of the free 

 hydrogen through some hundreds or thousands of feet of shales and 

 limestones. The free hydrogen originally present should still occur 

 in the gas of different regions and be recognizable by chemical 

 tests. If, on the other hand, natural gas is a stored product, shut 

 in for long ages, it might seem possible that comparatively impervi- 

 ous rock strata would not have sufficed to prevent the escape of 

 this highly diffusible constituent in the course of time. 



No hypothesis regarding the origin of natural gas can be accepted 

 as satisfactory if it should require the assumption that the chemical 

 changes involved in the process are such as to lead to the production 

 of much free hydrogen, unless it can be positively demonstrated 

 that free hydrogen occurs as a common constituent of the gas which 

 flows from a drill hole. 



The foregoing criticisms have been directed more particularly to 

 the hypothesis in so far as it relates to natural gas. The author of 

 the hypothesis has apparently avoided a distinction between natural 

 gas and petroleum, and to the various hydrocarbons, liquid or 

 gaseous, he assigns a common origin. It has been common to 

 consider such compounds as closely related genetically. Yet this 

 supposition may not have sufficient basis. Mabery {American 

 Chei?iical Journal, 1896, p. 43) has shown that benzene and its 

 homologues occur in some of the Ohio and Canadian petroleums. 

 Lengfeld and O'Neill {American Chemical Journal, 1893, p. 19) 

 have also discovered members of the same series of hydrocarbons in 

 petroleum from southern California. Similar observations have 

 been made by other authors. 



The composition of natural gas is such as to suggest that it has 

 been produced by reactions occurring at low temperature, and there 

 is reason to suppose that it has not been exposed to temperatures 

 exceeding 500° C, since the time of its formation, as experiments 

 demonstrate that at temperatures ranging from this point up to that 

 of melting gold, its constituents suffer more or less complete dissoci- 



