THE natural flow of an oil well may recede either from the exhaustion of the oil supply or as the result of a stoppage of the pores of the oil-bearing rock cutting off the free supply of oil. In the past, some what drastic methods have been tried to overcome this drawback, but they are difficult to carry out, especially at a depth which may be half a mile below the surface. When the well is in a limestone forma tion, it has now been discovered that it is possible to open it up again by treatment with successive quantities of 10 or 15 per cent hydrochloric acid, which dissolve new channels in the calcareous rock and permit of a new flow of oil. The use of hydro chloric acid is only made possible by the addition to it of 1–5 per cent of an arsenic compound, which inhibits the action of the acid on the metallic casing and pump tubes of the well. Other inhibitors,including certain organic nitrogen bases, have been discovered but the arsenic compounds are the most convenient to apply in practice. The discovery has been made by the Dow Chemical Co. in partnership with the Pure Oil Co., and patented as the Dowell process: it is described in greater detail in the News Edition of Industrial and Engineering Chemistry for February 20. The use of acid made inactive towards metal surfaces is a novel and important one: it may be a revolutionary factor in oil production. Further, it is likely to be beneficial in natural gas production and in other directions. It is certainly an achieve ment to be able to control the action of a strong acid as a boring agent half a mile below the surface.