The next building was the treating-house, where stand huge tanks containing the oil as drawn from the testing-room. From these it is conducted by pipes to the iron vats, called treating-tanks, and there mixed with vitriol, alkali, and other chemicals, in certain exact proportions. The monster in the next building is now set in operation, and forces a stream of compressed air through a pipe from top to bottom of the tank, whence, following its natural law, it loses no time in ascending to the surface with a noisy ebullition, just like, as Jimmy remarked, "a big pot over a sthrong fire." This mixing operation was formerly performed by hand in a much less effectual manner, the steam air-pump being a recent improvement. The work of the chemicals accomplished, the oil is cleansed of them by the introduction of water, and after an interval of quiet the mass separates so thoroughly that the water and chemicals can be drawn off at the bottom of the vat with very little disturbance to the oil. From the treating-house the perfected oil is drawn to the tanks of the barrelling-shed, and filled into casks ready for exportation. A large cooper's shop upon the premises supplies a portion of the barrels, but is principally used in repairing the old ones. The oil is next teamed to the Creek, and either pumped into decked boats, to be transported in bulk, or, still in barrels, is loaded upon the ordinary flatboats. During a large portion of the year, however, neither of these can make the passage of the shallow Creek without the aid of a "pond-fresh." This occurs when the millers near the head of the Creek open their dams, and by the sudden influx of water give a gigantic "swell" to the boats patiently awaiting it at every "farm," from Schaeffer's to Oil City.