202 white: relations between coal and PETROLEU]\r 



the liquid distillates, the petroleums, found in different regions 

 reveal any differences corresponding to the stages in the regional 

 alteration of the carbonaceous residues. 



In entering on the observations necessary to the comparison 

 of petroleums from regions of varying degrees of alteration of 

 the organic detrital deposits, many diifculties are encountered: 

 There is no adequate volume of chemical analyses of petroleums 

 from different oil fields and geologic formations. On the other 

 hand, we find fractionation, lacking as to uniformity of method, 

 and often made from deteriorated or unreliable samples, for 

 commercial information. In comparatively few cases is the pro- 

 portion of any single hydrocarbon determined. The only data 

 obtained by approximately standardized methods and covering 

 samples of geographic and geologic range, suli-cient for com- 

 prehensive inter-regional comparisons, consist of specific gravity 

 determinations. These, though they are the best criteria at 

 hand, are also far from satisfactory, for, while in general the 

 oils of lightest gravity are of the highest rank, containing the 

 largest amounts of light (saturated) hydrocarbons, with largest 

 proportions of hydrogen, and of lightest density, the gravity 

 records can not take the place of chemical determinations of 

 the hydrocarbon compounds in the study of the genetic features 

 and the chemical classification of the petroleums. Furthermore, 

 the gravity records contain unknown errors, due to the condi- 

 tions of the samples as well as to the sources of the latter. Many 

 of them represent shallow sand oils, from which the lighter ele- 

 ments have escaped up the dip or to the surface; which have 

 stood in tanks or in wells intermittently pumped; which are 

 affected by meteoric waters; or which were taken from mere 

 seeps, shafts or springs. On the whole, however, the gravities 

 of representative samples approximately show the rank of the 

 petroleums and may, therefore, be utilized in a rough compari- 

 son of the oils from different regions. In view of the present 

 lack of standardized analytic or fractionative criteria in sufficient 

 abundance from both the stratigraphic and geographic stand- 

 points for detailed studies, the conclusions which I have to offer 

 are to be regarded as a report of progress. 



