160 



one sunk, was 71 feet deep — they vary from this point to 

 500 or 600 feet. Even in the same locality wells are of the 

 most various depths, varying one or two hundred feet. 

 Most of the spouting wells are bored to a considerable 

 depth. 



The quality of the oil too is by no means the same. The 

 difference is in specific gravity, color, smell, and per cent 

 yielded in refining. These variations, however, are here 

 found to be not between the oil of wells in the same vici- 

 nity, but is more marked between different oil regions. 

 Thus the oil of the Canada oil wells is of a much darker 

 color, and of a more disagreeable odor than that from 

 Pennsylvania. So too that from Mecca, Ohio, is easily 

 distinguishable from any other. 



Y. Modes of Refining and the Different Products — 

 The oil as obtained from the wells is exceedingly impure, 

 of a bluish black color, and as has been said of a pungent, 

 offensive odor. Much water usually flows or is pumped out 

 with the oil, but separates from it readily by its greater 

 specific gravity. The subsequent purification is conducted 

 partly by distillation by heat and partly by agitation with 

 chemical reagents. The oil is first put into large retorts of 

 cast or boiler iron, and subjected to a heat gradually in- 

 creasing till it has reached 600° or 800°. The entire evapor- 

 able matter of the crude oil is thus driven over and collect- 

 ed by condensation. About 10 or 12 per cent of solid mat- 

 ter remains behind, which form a sort of coke in the bottom 

 of the retort. The oil in a great measure has lost its color 

 and is more limpid than before, but retains most of its dis- 

 agreeable odor. 



The next process is to agitate the oil with sulphuric acid. 

 This is done in large cylinders, into which the oil with about 

 six or eight per cent of acid is put,and then rapidly whirled 

 round by means of stirrers. After this process the oil is 

 suffered to rest, the acid sinks to the bottom, and carries 



