[Illustration: The Drader Well in the Moreni field, Roumania. This well was producing 20,000 barrels daily when it caught fire] [Illustration: Burkburnett in northern Texas, showing development since August, 1918] The drilling equipment is called by the oil workers a “string of tools.” It consists of a rope socket, a stem or sinker about thirty feet long and five inches or more in diameter, depending on the size of the hole to be drilled, with a bit at the bottom. Attached to a string of tools is a set of what are known as “jars,” which take their name from their function of enabling the driller to jar the sinker loose. Manila or wire cable is wound upon a large reel known as the “bull wheel” which is placed in the base of the derrick and a section of this cable passes over a crown pulley at the top of the derrick and is fastened to the rope socket and “string of tools.” The drilling movement is created by a power-driven walking beam which is a heavy timber working on an axis. This walking beam rocks up and down, with a stroke of three or four feet; thus the tools are raised and dropped at regular intervals, their great weight giving them a stroke equal in force to a steam hammer. The power used is ordinarily steam and the cable is connected with the walking beam by a temper screw, which enables the driller to lower the tools and handle them with ease and accuracy. Another method of growing importance is the rotary system, perfected within the present century in the Gulf Coast field of Texas and Louisiana and which in many sections is coming into common use. Its special advantage is speed in soft or caving formations. It consists of a perforated fish-tail bit screwed to a string of drill pipe, which projects up through the derrick platform and is rotated at the rate of about two hundred revolutions per minute by a turn-table. The top or “grip” joint of the pipe is usually made square, or hexagonal, to supply a good bearing surface for the turn-table. The tools are suspended by means of a swivel at the top of the grip joint. This swivel also has a hose connection through which thin mud is pumped down to the bottom of the hole. The circulation of this mud carries out the cuttings made by the fish-tail bit, and also serves to plaster up the side of the hole and thus prevent caving. The column of mud in the hole exerts a hydrostatic pressure which absolutely prevents quicksand from running in and causing the hole to collapse. A rotary appliance has been known to drill two hundred feet or more in twelve hours, but usually so high a rate of speed is impossible, since the pipe stem has to be pulled out at frequent intervals and the bit replaced. The fact that the delicate fish-tail bit grows smaller with wear creates this necessity.