X.] THE OIL-BEARING LIMESTONE OF CHICAGO. 173 



by breaking up some pounds of the specimens above mentioned, 

 and supposed to represent an average of the rock exposed in 

 the quarry, were reduced to coarse powder in an iron mortar. 

 Of these two portions, respectively, 1 00 and 1 38 grammes were 

 dissolved in warm dilute hydrochloric acid. The tarry residue 

 which remained in each case was carefully collected and treated 

 with ether, in which it was readily soluble with the exception 

 of a small residue. This, in one of the samples, was found 

 equal to .40 per cent, of which .13 was volatilized by heat with 

 the production of a combustible vapor having a fatty odor ; 

 the remainder was silicious. The brown ethereal solutions were 

 evaporated, and the residuum, freed from water and dried at 

 100 C., weighed, in the two experiments, equal to 1.570 and 

 1.505 per cent of the rock, or a mean of 1.537. It was a viscid 

 reddish-brown oil, which, though deprived of its more volatile 

 portions, still retained somewhat of the odor of petroleum 

 which is so marked in the rock. Its specific gravity, as deter- 

 mined by that of a mixture of alcohol and water in which the 

 globules of the petroleum remained suspended, was .935 at 

 16 C. Estimating the density of the somewhat porous dolo- 

 mite at 2.6, we have the proportion .935 :2.600::1. 537:4.260; 

 so that the volume of the petroleum obtained equalled 4.26 per 

 cent of the rock. This result is evidently too low, for two rea- 

 sons : first, because the rock had already lost a part of its oil, 

 while in the quarry and subsequently, before its examination ; 

 and secondly, because the more volatile portions had been 

 dissipated in the process of extraction just described. 



In assuming 100.00 parts of the rock to hold 4.25 parts by 

 volume of petroleum, we are thus below the truth in the follow- 

 ing calculations. A layer of this oleiferous dolomite one mile 

 (5,280 feet) square and one foot in thickness will contain 

 1,184,832 cubic feet of petroleum, equal to 8,850,069 gallons 

 of 231 cubic inches, and to 221,247 barrels of forty gallons 

 each. Taking the minimum thickness of thirty-five feet, as- 

 signed by Mr. Worthen to the oil-bearing rock at Chicago, we 

 shall have in each square mile of it 7,743,745 barrels, or in 

 round numbers seven and three quarter millions of barrels of 



