MABRRY. — CONSTITUENTS OF PETROLEUM. 123 



it can, I think, be stated with confidence that distilhilions many times 

 repeated under constant conditions may be expected to yield products 

 wliose composition can be determined, after suitable purification, as accu- 

 rately as the methods of analysis will permit. But hydrocarbons sepaiated 

 from petroleum in this manner, before purification, may be contaminated 

 by other bodies whose boiling points are nearly the same. As an illus- 

 tration, to ascertain whether Ohio petroleum contains a hydrocarbon 

 boiling at 162°, a course of fractional separations under 730 mm. was 

 repeated fifty times, forty-five times within one degree. One portion 

 after treatment with fuming sulphuric acid had its specific gravity changed 

 from 0.7717 to 0.7535, but It still distilled within the same limits. 

 Another portion of the same distillate, after treatment with common 

 concentrated sulphuric acid, gave a product with the same specific gravity 

 and the same boiling point as the oil before treatment. The crude distillate 

 contained a certain amount of mesitylene, boiling point 163°, sufficient, as 

 will appear later, to affect seriously the percentages of carbon and hydrogen. 

 In the main, the hydrocarbons described in this paper as collecting be- 

 tween 160° and 216° have the same boiling points as those described by 

 Warren, except one which collected at 162°. It is peculiar that these 

 bodies have nearly the same boiling points as the naphtenes separated by 

 Markownikoff from the Russian oil. In previous investigations on these 

 hydrocarbons, except those of Warren, evidently the course of distillation 

 was not carried far enough to separate with any degree of purity the 

 individual constituents. In the light of Warren's distillations and those 

 here presented, it is evident that Pelouze and Cahours could not have 

 carried their separations far enough to obtain individual products. Con- 

 cerning the thoroughness of Warren's separations there can be no ques- 

 tion. But the deficiency in his work on the hydrocarbons now under 

 consideration was the result of the limited knowledge then prevailing con- 

 cerning the general composition of petroleum. The aromatic hydrocar- 

 bons, the oxygen compounds, and the nitrogen compounds, were not then 

 recognized, or were merely suspected as constituents of petroleum. In 

 the purification of his distillates, the single method adopted by Warren 

 consisted in boiling with sodium, as shown by the following statement : 

 " I must state, however, once for all, that, unless specially mentioned, no 

 one of the bodies operated upon had received any chemical treatment 

 except that of boiling with sodium.*' * But that Warren suspected the 

 presence in his distillates of other bodies is indicated by a quotation from 



* Proc. Amer. Acad , XXVII. 66. 



